CHAPTER 3 - DOPED IN LEAD BISMUTH ALUMINUM-BORATE …shodhganga.inflibnet.ac.in/bitstream/10603/10071/1/3rd chapter.pdf · lead–bismuth–aluminum-borate glasses have been studied

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CHAPTER 3

SPECTROSCOPIC PROPERTIES OF Nd3+

- DOPED IN

LEAD–BISMUTH–ALUMINUM-BORATE GLASSES WITH

CONCENTRATION VARIATION

ABSTRACT

________________________________________________________________________

The effect of Nd3+

ion concentration on the physical and spectroscopic properties of

lead–bismuth–aluminum-borate glasses have been studied for the compositions:(70-

x)B2O3+20PbO+5Bi2O3+5Al2O3+xNd2O3 where x= 0.1, 0.5, 1.0, 1.5, 2.0 and 3.0 mol%.

From the room temperature absorption spectra, various spectroscopic parameters have

been computed. The Judd-Ofelt intensity parameters Ωλ (λ=2,4 and 6) have been evaluated

and used to obtain the radiative transition probabilities (AR), radiative life-times (τR),

branching ratios (βR) and absorption cross-sections (σa). Stimulated emission cross-

sections (σe) for the lasing levels 4F3/2→

4IJ (J=9/2, 11/2 and 13/2) were evaluated from

fluorescence spectra. Optical band gap values were estimated. FT-IR spectra were

recorded and analyzed.

_____________________________________________________________________

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3.1. Introduction

Physical and spectroscopic properties of silicate, phosphate and borate glasses doped

with various rare earth ions offer many commercial and technological applications.

[21,91,92]. Heavy metal oxide (HMO) glasses find their importance as host matrices for

good lasing candidates because of their low phonon energy, high density, high refractive

index, optimum band width, high mechanical and thermal stability, corrosion resistance

and good solubility of rare earth ions [15,21-23]. Initially the laser efficiency increases

with the concentration, maximum at optimum level and decreases at higher concentrations

due to non radiative self-quenching processes [21]. Hence, the incorporation of HMOs such

as PbO or Bi2O3 into the borate glass matrix leads to an increase in its luminescence

quantum efficiency [21]. The effect of lead-borate, bismuth-borate and lead-bismuth-

borate glasses on the optical properties of Nd3+

ion have been reported [21, 23-25].

Motivated by these works lead-bismuth-aluminum-borate glasses doped with Nd3+

were

prepared and their physical and spectroscopic properties were studied with variation of

Nd3+

concentration.

Laser active medium should have high gain, high energy storage capability, low optical

losses which depend on stimulated emission cross-section, fluorescence life-times and

optical efficiency [15, 93]. The absorption spectrum of Nd3+

ions in a typical glass range

from ultraviolet to the infrared region. The stimulated emission cross-section is in the

3

intermediate range [94]. The compatibility of borate glasses as host materials for rare earths

is encouraging in the areas like wave guide lasers and optical amplifiers [93, 94].

For all the present glass matrices optical absorption and emission spectra were recorded

at room temperature. The spectroscopic parameters like Racah (E1, E

2 and E

3), Slater-

Condon (F2, F4 and F6) and bonding parameter (δ) were evaluated from the spectral data.

The Judd-Ofelt (JO) intensity parameters (Ω2 , Ω4 and Ω6 ), transition probabilities (A), life

times (ηR), branching ratios (βR) and absorption (ζa) and emission (ζe) cross-sections have

been computed. The significant lasing transitions 4F3/2

4IJ (J = 13/2, 11/2 and 9/2) have

been studied. Optical band gap values were estimated. FT-IR spectra were recorded and

studied for structural changes in the 3D glass network. The present results are compared

with some of the reported glasses doped with varying Nd3+

ion concentration.

3.2. Experimental details

BLABIN1-6: (70-x) B2O3+20PbO+5Bi2O3+5Al2O3+xNd2O3 (where x = 0.1, 0.5,

1.0, 1.5, 2.0 and 3.0 mol%) glasses were prepared by melt quenching technique.

Appropriate amounts of B2O3, PbO, Bi2O3, Al2O3 and Nd2O3 of 99.9% purity were

thoroughly mixed and grinded using an agate mortar in 10g batches. This mixture is

transferred into a silica crucible and kept in an electric furnace initially for 30 min between

400 and 4500C then for 1 hour at 1000

0C for melting and then poured onto a pre-heated

brass plate and air quenched. The glasses so obtained were annealed at about 4000C for 8 h

to remove internal mechanical stress and then after cooling to room temperature samples of

good optical quality were selected and polished in order to study the physical and

spectroscopic properties. Refractive indices were determined by Brewster angle method at

4

a wavelength of 543 nm. The amorphous nature of the samples was confined by XRD

spectra obtained by using Shimadzu - XD 3A diffractometer. Perkin Elmer Lambda 950

UV-Vis-NIR spectrophotometer is used to record the absorption spectra at room

temperature in the wave length range of 400-900 nm. The NIR emission spectra were

recorded in the range of 800-1500 nm by JOBIN-YVON Fluorolog-3 spectrofluorimeter, at

room temperature. The FT-IR spectra were recorded using KBr pellet method on Thermo

Nicolet-5700 FT-IR Spectrophotometer in the wave number range 4000– 400 cm-1

.

3.3 Results and discussion

3.3.1 Physical properties

Physical properties such as density (d), molar volume (VM), neodymium ion

concentration (N), dielectric constant ( ), reflection loss (R), molar refractivity (Rμ), inter-

ionic distance (ri), polaron radius (rP), field strength (F), electric susceptibility (χe) and

numerical aperture (NA) were evaluated using relevant expressions 2.1- 2.12 for the glass

matrices BLABIN:1-6 and are presented in Table 3.1.

The laser beam emanating from the lasing material is affected mainly by RE ion

concentration. The variation of density and molar volume with concentration of Nd2O3 is

graphically presented in Fig 3.1. The density decreases from 0.1 to 0.5 mol%, then

increases up to 1.5 mol%, again decreases up to 2.0 mol% and then increases at higher

concentrations. The possible reason of decrease in density of the host material could be the

formation of non-bridging oxygen atoms around 0.5 and 2.0 mol% concentration of

Nd2O3. The clustering of RE ions can be one of the factors which contribute to the

variation of the density at higher concentrations. The behavior of molar volume follows an

5

opposite trend to the density as expected. The concentration of the number of luminescent

centers (N) is found to be densely distributed because of the higher values of the glass

density (d) and refractive index (n) and is comparable to other host glasses [21,25,94].

The polaron radius (rP) is less than inter-ionic distance (ri) and hence high field strength

(F). Polaron radius and inter-ionic distances decrease with increase of Nd3+

concentration.

Fig. 3.1 Variation of (a) Density and (b) Molar Volume with Nd2O3 Concentration

Luminescent centers (N) are found to be densely distributed because of the higher values

of the glass density (d) and refractive index (n) and is comparable to other host glasses

[21,25,94]. The polaron radius (rP) is less than inter-ionic distance (ri) and hence the high

field strength (F). Polaron radius and inter-ionic distances decrease with increase of Nd3+

6

Table 3.1: Various physical properties of Nd3+

: BLABIN 1-6 glasses

S.No. BLABIN→

Parameter↓

1 2 3 4 5 6

1 Refractive index, n 1.740 1.741 1.743 1.744 1.746 1.749

2 Density d (gm/cm3) 4.094 3.970 4.050 4.174 3.966 4.779

3 Average molecular wt (g) 203.58 185.28 207.45 209.55 211.67 215.57

4 Molecular volume (VM)

(cm3)

49.73 50.65 50.51 50.20 53.37 45.11

5 Optical path length(cm) 0.280 0.257 0.292 0.268 0.290 0.295

6 Nd3+

conc. (1020

ions /cc) 0.21 0.95 1.93 2.96 3.46 5.85

7 Optical dielectric constant,

ε

3.028 3.031 3.038 3.042 3.049 3.059

8 Reflection loss R (%) 7.294 7.308 7.337 7.352 7.380 7.424

9 Molar refractivity Rµ

(cm3)

20.057 18.841 20.721 20.331 21.659 18.358

10 Inter-ionic distance ri (Å) 36.538 21.749 17.233 14.953 13.859 11.953

11 Polaron radius rP (Å) 14.727 8.766 6.946 6.027 5.586 4.818

12 Field strength F (10+15

cm-

2)

0.598 1.687 2.687 3.568 4.154 5.583

13 Electric susceptibility χe 0.1613 0.1616 0.1621 0.1624 0.1630 0.1638

14 Numerical aperture (NA) 0.25 0.25 0.25 0.25 0.25 0.25

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concentration. All the glasses under investigation have numerical aperture (NA) about 0.25

indicating that optical fibers made of these glass compositions will accept large amount of

light from the source. Hence these transparent glasses are suitable as core material for

optical fibers [84].

3.3.2. Absorption spectroscopic parameters

The absorption spectra of the Nd3+

: BLABIN 1-6 glass matrices in the wavelength range

of 400-900 nm are shown in Fig. 3.2. A comparison of the optical absorption spectra of the

present glasses with the standard wavelength chart of Nd3+

[14,21,53,63,98] results in the

identification of the spectroscopic transitions 4F3/2,

4F5/2+

2H9/2,

4F7/2+

4S3/2,

4F9/2,

2H11/2,

4G5/2+

2G7/2,

4G7/2+

4G9/2+

2K13/2,

2G9/2+

4G11/2,

2P1/2 ←

4I9/2 [53]. The experimental energy

levels of Nd3+

ions in the present glasses are obtained from the absorption spectra and are

collected in Table 3.2. The rms deviation range from ± 40.13 to ± 57.47 and is in good

agreement with the literature. The variation of total intensity with Nd2O3 concentration of

some selected bands is shown in Fig.3.3. The energy level analysis [15, 63, 92, 99, 100] by

the Hamiltonian model expressed in the form of free-ion (HFI) with the help of f- shell

empirical program [14,15]. The HFI representing the energy level structure of Nd3+

(4f 3)

ion is defined as

…(3.1)

8

where k=2,4 and 6; i = 2,3,4,6,7 and 8; and j = 0,2 and 4. The operators and their associated

parameters were written according to conventional notation and meaning [14,15,92].

Among the various interactions that contribute to the total free-ion Hamiltonian, the inter-

electronic (Fk) and the spin-orbit (ξ) interactions are the major contributors and they govern

the 2S+1

LJ contributions to the energy level positions [15, 96]. The other terms will only

give corrections to the energy of these levels without removing their degeneracy. In Table

9

3.3 the best-fit free-ion parameters Fk, ξ, α, β and γ values are collected. The sum of Slater

integrals ΣFk

indicating the net electrostatic interaction experienced by Nd3+

ions in the

host matrix, is also given in this table. ΣFk

trend suggests that Nd3+

ions experience

relatively more electrostatic bonds in BLABIN:1 than in other glass hosts [15,53,63,99].

The ΣFk

value shows the decreasing tendency with the increase in the concentration of

Nd3+

except for 2 mol%. The hydrogenic ratios, F2/F

4 (~1.45) and F

2/F

6 (~1.89), for

Lasing

level BLABIN1 BLABIN2 BLABIN3 BLABIN4 BLABIN5 BLABIN6

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Table 3.2 : Experimental energies of Nd3+

: BLABIN 1-6 glasses

BLABIN:1-6 glass systems are in good agreement with those Nd3+

doped glass systems

[15] indicating that the radial integral part of the f-orbital of Nd3+

ions remains unchanged

even though the concentrations are changed. This may mainly due to shielding effect

experienced by the 4f electrons by the 5s25p

6 orbitals [15].

Nephelauxetic ratio cn

a

where c and a refer to the spectral energies (cm

-1) in the

host under investigation and the aqua-ion respectively, and bonding parameter

4F3/2 11494 11481 11481 11481 11468 11468

4F5/2 12500 12500 12500 12500 12484 12484

4F7/2 13550 13500 13531 13531 13531 13513

4F9/2 14815 14749 14749 14749 14749 14728

2H11/2 16000 16000 16000 16000 16000 16000

4G5/2 17212 17212 17212 17212 17212 17212

4G7/2 19120 19083 19083 19083 19083 19083

4G9/2 19569 19569 19569 19569 19569 19569

2G9/2 21186 21142 21142 21097 21097 21097

4G11/2 21598 21505 21598 21598 21598 21598

2P1/2 23310 23364 23310 23310 23310 23310

rms

dev.

±50.14 ±40.13 ±56.89 ±57.32 ±56.54 ±57.47

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Table 3.3 : Spectroscopic parameters of Nd3+

: BLABIN 1-6 glasses

Parameter 1 2 3 4 5 6

E1(cm

-1) 5710.20 4993.41 4881.05 4872.24 5100.45 4874.63

E2(cm

-1) 25.38 25.74 25.53 25.65 25.71 25.74

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…(3.2)

E3(cm

-1) 490.08 489.17 489.21 489.78 490.02 490.11

ξ4f (cm-1

) 922.77 904.71 914.38 910.55 913.23 909.12

α (cm-1

) 0.15 -3.92 -3.65 -3.87 -2.78 -3.91

β (cm-1

) 307.38 446.50 460.83 475.52 455.33 508.06

γ(cm-1

) -3611.17 71.54 432.46 502.49 -610.82 505.89

E1/E

3 11.65 10.21 9.98 9.95 10.41 9.95

E2/E

3 0.05 0.05 0.05 0.05 0.05 0.05

F2 (cm-1

) 350.72 334.63 331.26 331.63 337.31 332.05

F4(cm-1

) 56.77 46.81 45.71 45.41 48.29 45.31

F6 (cm-1

) 6.86 5.35 5.09 5.07 5.56 5.08

F2/F4 0.01 0.01 0.01 0.01 0.01 0.01

F4/F6 1.22 1.30 1.33 1.33 1.28 1.32

F2

(cm-1

) 78912.5 75292.6 74533.3 74616.0 75895.0 74712.3

F4

(cm-1

) 61821.6 50976.0 49772.8 49449.2 52588.7 49346.3

F6

(cm-1

)

ΣFk

50478.3

191212.4

39357.1

165625.7

37446.1

161652.2

37312.3

161377.5

40952.9

169436.6

37361.3

61419.9

δ 0.828 0.961 0.923 0.947 0.963 0.983

n 1.7401 1.7413 1.7428 1.74424 1.74572 1.74868

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where n is the average value of n, have been evaluated. The RE ion-ligand bond will be

covalent or ionic depending respectively on positive or negative sign of value [43,74].

For the present glass matrices value ranging from + 0.828 to + 0.983 indicates that the

RE ion-ligand bonds are strong and covalent.

3.3.3. Spectral intensities and Judd-Ofelt parameters

The experimental oscillator strengths of the absorption transitions can be obtained

from the relation [53, 63,100] fexp = 4.318 x 10-9

( ) d where ε (ν) = OD/ct is the

molar extinction coefficient at mean energy ν (cm-1

), with OD being the optical density, c

being the molar concentration of the RE ions and t is the optical length of the glass[15].

The intensities of all absorption bands have been evaluated using the area method. The rms

deviations between experimental and calculated oscillator strengths (fexp and fcal) presented

in Table 3.4 range from ± 0.7 to ± 2.43 show the validity of Judd-Ofelt theory. Using the

oscillator strengths, the values of the reduced matrix elements and other parameters, JO

intensity parameters Ωλ (λ = 2,4,6) have been computed by the least- square fit [51,52] and

are collected in Table 3.5. Since the reduced matrix elements are host invariant, the values

reported in literature [53, 63, 84] have been used for the calculations. Some of the

absorption bands overlap with each other and in those cases the matrix elements

2

U

of

the corresponding transitions were summed for JO analysis [15]. In crystals and glasses

the RE ions are distributed over a large number of non-equivalent sites and the intensity

parameters are the average values of Ωλ ( λ = 2,4,6) from all the sites [21]. The obtained

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values of Ωλ are in the order 6 2 4 for all the glasses under study .

Table 3.4 : Experimental and calculated oscillator strengths ( x 10-6

) and rms

deviation of Nd3+

: BLABIN 1-6 glasses.

According to Krupke [101] Ω2 and Ω6 values mainly depend on the transition

intensities of 4I9/2 →

4G5/2+

2G7/2 and

4I9/2 →

4F7/2+

4S3/2 respectively. These transitions in

the absorption spectra split into two peaks by Stark-splitting due to crystal-field. From

Fig. 3.2, it is evident that the resolution of Stark-splitting of the hypersensitive transition

4I9/2→

4G5/2+

2G7/2 decreases with increasing concentration. Hence for BLABIN: 1-4 there

is visible resolution and for BLABIN: 5 and 6 the resolution is poor indicating for

Level

BLABIN1 2 3 4 5 6

f exp f cal f exp f cal f exp f cal f exp f cal f exp f cal f exp f cal

4F3/2 - 1.74 1.65 2.57 2.57 2.86 2.86 2.22 1.84 2.13 3.29 2.46

4F5/2+

2H9/2 8.86 8.21 9.40 9.14 9.14 10.30 10.30 10.39 12.89 11.45 11.50 11.6

4F7/2+4S3/2 9.11 9.83 9.62 9.95 9.95 11.24 11.24 11.71 8.04 12.32 12.42 13.5

4F9/2 0.53 0.73 0.80 0.77 0.77 0.86 0.86 0.85 1.60 0.85 0.96 0.85

2H11/2 0.15 0.20 0.19 0.21 0.21 0.24 0.24 0.22 0.41 0.22 0.26 0.24

4G5/2+

2G7/2 22.0 22.2 26.0 26.0 26.0 24.6 24.6 28.1 28.4 28.5 28.6 29.0

4G7/2+

4G9/2+

2K13/2 8.23 5.63 8.40 7.00 7.00 7.48 7.48 10.27 4.77 10.42 8.54 10.9

2G9/2+

4G11/2 1.71 0.86 2.28 1.12 1.12 1.25 1.25 2.39 1.63 2.44 1.42 2.60

2P1/2 - 0.35 0.36 0.62 0.62 0.69 0.69 0.42 0.08 4.33 0.80 0.51

rms dev. ±1.1 ±0.7 ±0.77 ±1.56 ±2.43 ±0.99

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BLABIN: 1-4 glasses Ω2 parameter value is mainly contributed by covalence parameters

rather than crystal-field parameters whereas for BLABIN: 5 and 6 the converse is true.

Stark-splitting of the transition 4I9/2 →

4F7/2+

4S3/2 is well resolved for BLABIN: 3-6

glasses.

Table 3.5 : Judd-Ofelt intensity parameters (Ωλ , λ = 2,4,6 )

( x 10-20

cm2) Nd

3+ : BLABIN 1-6 glasses

The Ω2 parameter indicates the covalent nature of the RE ion-ligand bond as well as

the asymmetric nature of the Nd3+

ion local environment. Increase of asymmetric nature of

RE ion site and increase of covalency of chemical bonds with the ligands cause an increase

in Ω2 value [14]. For the present glass systems Ω2 values are in the order of BLABIN: 1 <

BLABIN: 2 > BLABIN: 3 < BLABIN: 4 >BLABIN: 5 <BLABIN: 6 indicating BLABIN:

BLABIN →

Parameter ↓ 1 2 3 4 5 6

Ω2 5.70 5.91 5.09 6.16 5.95 6.28

Ω4 2.29 4.06 4.54 4.78 5.30 4.95

Ω6 6.09 6.05 6.84 7.09 7.54 8.15

Ω4 / Ω6 0.38 0.67 0.66 0.67 0.70 0.61

Ω2 + Ω4 + Ω6 14.08 16.03 16.47 18.03 18.79 19.38

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4,5 and 6 (higher concentration) glasses exhibit more covalence and higher asymmetry of

Nd3+

ion local environment compared to other three glasses (lower concentration). The Ω4

and Ω6 parameters are related to rigidity of the host matrix [14]. These values indicate that

the rigidity of the present glasses under study increases with increasing concentration.

Spectroscopic quality factor χ = Ω4 / Ω6 determines the lasing efficiency of the host.

BLABIN: 1 glass has χ = 0.38 equivalent to that of Nd: YAG laser [102] indicating it as a

good lasing material. For BLABIN:1-6 glasses χ range from 0.38 to 0.70 indicating these

are better lasing hosts than those like fluoride, oxide and phosphate glasses reported in

literature [15,102-104]. The variation of total intensities of the bands of the transitions

4F5/2+

2H9/2,

4F7/2+

4S3/2,

4G5/2+

2G7/2 and,

4G7/2+

4G9/2+

2K13/2 ←

4I9/2 with Nd2O3

concentration, is the fingerprint of changes in the structure of the glass. The changes in

the line profiles indicate that small change in the concentration of Nd2O3 causes more

changes in the network structure of the glass and the local environment of the optically

active ion.

3.3.4 Radiative properties

The obtained Ωλ (λ = 2,4,6) values from the absorption measurements have been

used to calculate the radiative transition probabilities (AR), radiative life-times (ηR),

branching ratios (βR) and absorption cross-sections (ζa) of the excited state 4F3/2. The

equations for the radiative transition probabilities A(SLJ, S1L

1J

1) for emission between J

manifolds, the electric dipole line strength and the magnetic dipole line strength are given

in chapter 1. For Nd3+

ion, the bands produced by the magnetic dipole mechanism have

very low spectral intensity compared to those produced by electric dipole mechanism.

Hence the term n3 Smd in the equation for A(SLJ, S

1L

1J

1) can be omitted [5]. Electric

17

dipole line strengths and radiative transition probabilities of certain lasing transitions of

Nd3+

: BLABIN 1-6 glasses are given in Table 3.6.

The radiative life times (R) [97] for certain lasing transitions presented in Table

3.7 indicate the order 2

H11/2 > 4F3/2 >

4F9/2 >

4F5/2 >

4G7/2 >

4G9/2 >

4G5/2 for all

the glasses. Transition probabilities are used to evaluate the fluorescence branching ratio

(R) [5, 15, 96, 97]. Branching ratios (βR) and integrated absorption cross-sections (ζa) of

certain lasing transitions of Nd3+

are given in Table 3.8.

Fluorescence spectra are given in Fig 3.4. The experimental and calculated

branching ratios (βR) and computed radiative lifetimes (ηR) for 4F3/2

4IJ (J = 13/2, 11/2

and 9/2) lasing transitions are presented in Table 3.9. The radiative property of the

transitions 4F3/2

4I13/2,

4I11/2 and

4I9/2 are characterized by the spectroscopic quality

factor χ and not by 2, as the tensor operator 2

2U is zero for all these transitions,

according to the triangle rule | J-J’| ≤ λ ≤| J+J’| [21,105-107]. 4F3/2

4I11/2 is a potential

lasing transition for Nd3+

ion (λ =1.06 μm). The radiative lifetime (ηR) has lowering trend

with increase in concentration of Nd2O3. Minimum values of ηR for BLABIN:6 glass with

3 mol% of Nd2O3 , reflect higher values of 4 and 6 with χ < 1. The transition 4F3/2 →

4I11/2 exhibits higher R value compared to other transitions. The magnitude of R did not

vary significantly whereas R decreases with increase of Nd3+

concentration (Fig 3.5) for

the above transition, indicating BLABIN: 1-6 glasses are good laser hosts.

18

The fluorescence band was integrated and divided by the peak intensity to yield an

effective line width [14, 74]. The stimulated emission cross–section of the laser transition

can be determined from the expression [15, 84,107]

4P 4 4

P 3/ 2 J2

eff

( ) A[( F );( I )]8 cn

…(3.3)

where P is the peak fluorescence wavelength, n is the refractive index, eff is the

effective line width of the transitions 4

F3/24IJ (J=13/2, 11/2 and 9/2) and

4 4

3/ 2 JA[( F );( I )]

is the radiative transition probability determined from the JO theory. The luminescence

properties (λP, ∆ λeff, (p),R) for the lasing transitions 4F3/2

4IJ (J = 13/2, 11/2 and 9/2)

are collected in Table 3.10. Spectroscopic quality factor helps to identify the channel

through which the excited metastable state 4F3/2 of Nd

3+ relaxes to the ground state. χ < 1

implies that the transition 4F3/2

4I11/2 is more intense than

4F3/2

4I9/2 and vice versa for χ

>1. For the potential lasing transition 4F3/2

4I11/2, (p) values exhibit the lowering order

with increase in Nd2O3 concentration and are comparable to those of commercial laser

glasses [15,22]. The high values of (p) and R indicate these glass matrices may be good

laser hosts. Experimental branching ratios (R exp) are obtained from the relative areas

under the emission peaks and are comparable with those predicted from the JO theory and

are collected in Table 3.9. The values of (p) for the 4F3/2

4IJ (J=13/2, 11/2 and 9/2)

transitions are comparable to the glasses reported in literature for phosphate and borate

glass host materials [87, 88, 89]. As can be seen from Fig 3.4, the emission bands are

affected by sizeable inhomogeneous broadening due to the large crystal-field distribution

around the RE ions which is the characteristic of the glasses under study [104].

19

20

Fig. 3.5 Variation of radiative lifetime of 4F3/2

4I11/2 transition with

Nd3+

concentration

21

Table 3.6 : Electric dipole line strengths (S’ed cm2x10

-22) and radiative transition probabilities A (s

-1) of certain lasing

transitions of Nd3+

: BLABIN 1-6 glasses

BLABIN→

Transition ↓

1 2 3 4 5 6

S’ed A S’ed A S’ed A S’ed A S’ed A S’ed A

4G9/2→

2K13/2 90.87 0.03 98.74 0.04 108.00 0.04 114.12 0.04 121.05 0.05 127.15 0.05

4G7/2 140.77 0.05 166.80 0.06 181.74 0.06 192.80 0.07 205.87 0.07 210.79 0.07

4G5/2 174.41 8.07 191.96 8.88 216.35 10.01 225.02 10.41 241.51 11.18 253.11 11.71

2G7/2 75.61 3.26 101.90 4.39 102.78 4.43 114.08 4.91 119.90 5.16 117.71 5.07

2H11/2 149.45 23.57 154.21 24.32 173.58 27.37 180.39 28.45 192.32 30.33 205.51 32.41

4F9/2 116.39 47.09 147.08 59.51 146.56 59.30 163.59 66.19 170.28 68.89 169.94 68.76

4F7/2 366.61 295.68 377.99 304.85 338.95 273.37 400.16 322.74 392.53 316.58 415.76 335.32

4S3/2 44.52 32.80 78.64 57.93 87.81 64.69 92.56 68.19 102.47 75.49 95.92 70.66

4F5/2 133.14 165.09 154.80 191.95 144.00 178.55 166.89 206.94 168.18 208.54 171.17 212.24

2H9/2 92.93 100.13 101.91 109.80 108.70 117.12 116.46 125.48 122.55 132.04 128.19 138.12

22

4F3/2 101.34 188.74 110.97 206.69 125.09 232.98 130.08 242.27 139.55 259.91 146.47 272.80

4I15/2 178.55 1503.22 203.07 1709.62 228.69 1925.32 238.12 2004.73 256.26 2157.47 266.04 2239.76

4I13/2 642.19 8300.42 730.40 9440.54 671.44 8678.46 783.16 10122.5 784.03 10133.8 803.09 10380.1

4I11/2 110.69 2058.12 172.57 3208.80 193.10 3590.42 202.94 3773.51 223.17 4149.53 214.24 3983.58

4I9/2 39.18 991.19 49.51 1252.62 54.93 1389.70 57.78 1461.87 62.42 1579.17 62.90 1591.33

4G7/2→

4G5/2 81.76 1.40 104.93 1.80 117.82 2.02 123.18 2.11 133.77 2.29 134.41 2.30

2G7/2 58.13 0.91 59.48 0.93 57.14 0.89 64.80 1.01 65.17 1.02 69.41 1.09

2H11/2 222.53 16.46 221.47 16.38 249.18 18.43 258.78 19.14 274.86 20.33 297.07 21.97

4F9/2 188.59 40.32 197.19 42.16 218.41 46.70 229.02 48.96 243.10 51.97 258.53 55.27

4F7/2 117.77 53.53 134.42 61.10 123.73 56.24 144.22 65.56 144.51 65.69 147.86 67.21

4S3/2 47.48 19.56 83.44 34.38 92.85 38.26 98.05 40.40 108.39 44.66 101.51 41.83

4F5/2 219.43 158.46 224.57 162.17 212.94 153.77 243.31 175.70 243.49 175.83 259.19 187.17

2H9/2 265.64 165.00 275.11 170.88 302.51 187.90 318.37 197.75 336.74 209.17 359.10 223.05

4F3/2 74.95 83.49 88.35 98.42 82.61 92.02 95.48 106.37 96.54 107.54 97.86 109.01

4I15/2 64.98 351.42 64.80 350.45 73.22 395.98 75.87 410.33 80.72 436.58 87.20 471.61

4I13/2 41.01 345.45 56.43 475.33 63.29 533.10 66.30 558.41 72.35 609.36 71.45 601.81

23

4I11/2 300.00 3673.92 339.52 4157.95 319.19 3908.92 367.44 4499.81 370.67 4539.34 380.89 4664.60

4I9/2 96.34 1618.30 128.27 2154.63 132.77 2230.20 145.22 2439.32 153.84 2584.10 151.92 2551.87

4G5/2→

2G7/2 81.76 0.00 104.93 0.00 117.82 0.00 123.18 0.00 133.77 0.00 134.41 0.00

2H11/2 8.87 0.09 8.86 0.09 10.01 0.10 10.37 0.10 11.03 0.11 11.92 0.12

4F9/2 82.38 7.57 83.24 7.65 93.61 8.60 97.28 8.94 103.46 9.51 111.28 10.22

4F7/2 144.69 45.08 163.53 50.96 178.15 55.51 188.82 58.84 200.75 62.55 208.35 64.92

4S3/2 41.01 11.01 72.54 19.48 80.88 21.72 85.33 22.91 94.42 25.35 88.35 23.72

4F5/2 182.08 111.07 210.78 128.57 195.02 118.96 226.71 138.29 227.92 139.03 232.20 141.64

2H9/2 4.85 2.39 7.24 3.57 7.92 3.90 8.42 4.15 9.17 4.52 8.86 4.36

4F3/2 286.83 316.23 304.70 335.94 266.89 294.26 319.75 352.53 312.03 344.02 326.46 359.93

4I15/2 2.80 21.94 2.78 21.82 3.15 24.65 3.26 25.54 3.47 27.17 3.75 29.38

4I13/2 37.34 488.79 43.25 566.15 48.68 637.31 50.72 664.01 54.67 715.64 56.46 739.11

4I11/2 124.07 2484.02 174.65 3496.72 195.79 3919.92 205.22 4108.68 224.27 4490.20 220.30 4410.62

4I9/2 627.26 17884.14 719.22 20506.1 667.82 19040.7 774.55 22083.7 778.92 22208.1 796.27 22702.8

2H11/2→

4F9/2 65.72 0.43 71.74 0.47 67.06 0.44 77.38 0.51 77.59 0.51 80.69 0.53

4F7/2 101.00 5.01 104.01 5.16 112.11 5.57 119.25 5.92 125.16 6.21 133.61 6.63

24

4S3/2 13.85 0.55 23.84 0.95 26.64 1.06 28.06 1.12 31.02 1.24 29.19 1.16

4F5/2 16.37 2.08 16.28 2.07 18.40 2.34 19.06 2.42 20.27 2.57 21.92 2.78

2H9/2 207.68 19.73 208.85 19.84 225.07 21.38 239.29 22.74 250.51 23.80 269.49 25.61

4F3/2 4.95 1.36 4.94 1.35 5.58 1.53 5.79 1.58 6.16 1.69 6.65 1.82

4I15/2 89.45 248.60 104.36 290.03 97.00 269.58 112.48 312.61 113.36 315.05 115.24 320.26

4I13/2 8.06 39.60 11.12 54.65 11.79 57.95 12.74 62.58 13.64 67.03 13.38 65.76

4I11/2 8.38 65.47 10.11 79.06 10.69 83.59 11.54 90.18 12.21 95.46 12.41 97.00

4I9/2 6.95 79.57 7.39 84.66 8.34 95.50 8.66 99.20 9.27 106.16 9.81 112.39

4F9/2→

4F7/2 121.78 0.85 139.66 0.98 142.48 1.00 156.62 1.10 162.92 1.14 167.64 1.17

4S3/2 1.20 0.01 1.60 0.01 1.80 0.01 1.88 0.01 2.05 0.01 2.04 0.01

4F5/2 84.00 3.15 92.88 3.48 103.00 3.86 108.07 4.05 115.39 4.33 120.66 4.52

2H9/2 29.53 0.69 31.06 0.72 27.34 0.64 32.65 0.76 31.89 0.74 33.49 0.78

4F3/2 68.91 8.14 69.35 8.20 78.34 9.26 81.21 9.60 86.47 10.22 93.14 11.01

4I15/2 396.02 859.47 483.25 1048.77 543.34 1179.19 567.07 1230.70 613.63 1331.73 624.77 1355.90

4I13/2 361.27 1499.85 397.76 1651.35 447.84 1859.25 466.04 1934.80 500.03 2075.92 523.97 2175.30

4I11/2 232.84 1621.52 237.43 1653.45 268.11 1867.07 278.07 1936.45 296.45 2064.49 317.99 2214.45

25

4I9/2 27.32 289.40 28.84 305.46 32.40 343.13 33.72 357.16 36.01 381.37 38.21 404.65

4F5/2→

2H9/2 13.75 0.00 19.33 0.00 20.69 0.00 22.23 0.00 23.92 0.00 23.39 0.00

4F3/2 56.28 0.36 67.36 0.43 63.54 0.40 73.10 0.46 74.25 0.47 74.95 0.47

4I15/2 139.97 206.38 139.20 205.24 157.29 231.93 162.97 240.31 173.35 255.61 187.43 276.37

4I13/2 285.60 980.75 316.51 1086.93 356.67 1224.83 371.05 1274.20 398.47 1368.38 416.77 1431.21

4I11/2 61.30 399.11 91.33 594.59 102.27 665.85 107.36 698.98 117.74 766.58 114.16 743.28

4I9/2 296.19 3183.53 336.36 3615.31 378.72 4070.59 394.37 4238.83 424.33 4560.84 440.70 4736.72

4F3/2→

4I15/2 17.04 22.14 16.95 22.01 19.15 24.88 19.84 25.78 21.10 27.42 22.82 29.64

4I13/2 127.37 443.14 126.67 440.70 143.14 498.00 148.31 515.99 157.75 548.85 170.56 593.42

4I11/2 281.02 2006.98 304.92 2177.65 343.79 2455.21 357.38 2552.25 383.11 2736.01 403.20 2879.54

4I9/2 85.94 1065.56 126.29 1565.83 141.46 1753.91 148.45 1840.53 162.67 2016.85 158.21 1961.58

26

Table 3.7 : Computed radiative lifetimes τR (µs) of certain lasing levels of Nd3+

:

BLABIN glasses.

BLABIN→

Lasing level↓

1 2 3 4 5 6

4G9/2 73 60 60 54 52 52

4G7/2 153 129 130 117 113 111

4G5/2 47 40 41 36 36 35

2H11/2 2163 1858 1855 1670 1614 1577

4F9/2 233 214 190 183 170 162

4F5/2 210 182 161 155 144 139

4F3/2 283 238 211 203 188 183

27

Table 3.8 : Branching ratios ( β) and integrated absorption cross sections (σa x 1018

cm-1

) of

certain lasing transitions of Nd3+

: BLABIN 1-6 glasses

BLABIN→

Transition↓

1

β σa

2

β σa

3

β σa

4

β σa

5

β σa

6

β σa

4G9/2→

2K13/2 0.00 0.07 0.00 0.07 0.00 0.08 0.00 0.08 0.00 0.09 0.00 0.09

4G7/2 0.00 0.10 0.00 0.12 0.00 0.13 0.00 0.14 0.00 0.15 0.00 0.15

4G5/2 0.00 0.64 0.00 0.70 0.00 0.79 0.00 0.82 0.00 0.88 0.00 0.92

2G7/2 0.00 0.27 0.00 0.36 0.00 0.37 0.00 0.40 0.00 0.42 0.00 0.42

2H11/2 0.00 0.82 0.00 0.85 0.00 0.95 0.00 0.99 0.00 1.05 0.00 1.12

4F9/2 0.00 0.88 0.00 1.11 0.00 1.10 0.00 1.23 0.00 1.27 0.00 1.27

4F7/2 0.02 3.47 0.02 3.57 0.02 3.20 0.02 3.77 0.02 3.69 0.02 3.90

4S3/2 0.00 0.41 0.00 0.72 0.00 0.80 0.00 0.85 0.00 0.94 0.00 0.87

4F5/2 0.01 1.46 0.01 1.69 0.01 1.57 0.01 1.82 0.01 1.83 0.01 1.85

2H9/2 0.01 0.97 0.01 1.06 0.01 1.13 0.01 1.21 0.01 1.27 0.01 1.32

4F3/2 0.01 1.27 0.01 1.39 0.01 1.56 0.01 1.62 0.01 1.74 0.01 1.82

4I15/2 0.11 3.70 0.10 4.20 0.12 4.72 0.11 4.91 0.11 5.27 0.12 5.45

4I13/2 0.61 15.33 0.57 17.42 0.52 15.98 0.55 18.61 0.53 18.60 0.54 18.99

4I11/2 0.15 2.98 0.19 4.65 0.22 5.19 0.20 5.44 0.22 5.98 0.21 5.72

4I9/2 0.07 1.17 0.08 1.48 0.08 1.64 0.08 1.72 0.08 1.85 0.08 1.86

4G7/2→

4G5/2 0.00 0.17 0.00 0.22 0.00 0.25 0.00 0.26 0.00 0.28 0.00 0.28

2G7/2 0.00 0.12 0.00 0.12 0.00 0.12 0.00 0.13 0.00 0.13 0.00 0.14

2H11/2 0.00 0.76 0.00 0.75 0.00 0.85 0.00 0.88 0.00 0.93 0.00 1.00

4F9/2 0.01 0.92 0.01 0.96 0.01 1.06 0.01 1.11 0.01 1.17 0.01 1.24

4F7/2 0.01 0.74 0.01 0.84 0.01 0.77 0.01 0.90 0.01 0.90 0.01 0.92

4S3/2 0.00 0.29 0.00 0.50 0.00 0.56 0.00 0.59 0.01 0.65 0.00 0.61

4F5/2 0.02 1.60 0.02 1.64 0.02 1.55 0.02 1.77 0.02 1.76 0.02 1.87

2H9/2 0.03 1.84 0.02 1.91 0.02 2.09 0.02 2.20 0.02 2.32 0.02 2.47

4F3/2 0.01 0.63 0.01 0.74 0.01 0.69 0.01 0.80 0.01 0.81 0.01 0.82

4I15/2 0.05 0.93 0.05 0.92 0.05 1.04 0.05 1.08 0.05 1.14 0.05 1.23

4I13/2 0.05 0.68 0.06 0.93 0.07 1.04 0.07 1.09 0.07 1.19 0.07 1.17

28

4I11/2 0.56 5.62 0.54 6.35 0.51 5.96 0.53 6.85 0.51 6.90 0.52 7.07

4I9/2 0.25 2.01 0.28 2.67 0.29 2.76 0.28 3.01 0.29 3.18 0.28 3.13

4G5/2→

2G7/2 0.00 0.01 0.00 0.02 0.00 0.02 0.00 0.02 0.00 0.02 0.00 0.02

2H11/2 0.00 0.03 0.00 0.03 0.00 0.03 0.00 0.03 0.00 0.03 0.00 0.04

4F9/2 0.00 0.53 0.00 0.54 0.00 0.60 0.00 0.62 0.00 0.66 0.00 0.71

4F7/2 0.00 1.40 0.00 1.58 0.00 1.72 0.00 1.82 0.00 1.93 0.00 2.00

4S3/2 0.00 0.38 0.00 0.67 0.00 0.74 0.00 0.78 0.00 0.87 0.00 0.81

4F5/2 0.01 2.21 0.01 2.55 0.00 2.36 0.01 2.74 0.00 2.75 0.00 2.79

2H9/2 0.00 0.05 0.00 0.08 0.00 0.09 0.00 0.09 0.00 0.10 0.00 0.10

4F3/2 0.01 4.24 0.01 4.50 0.01 3.93 0.01 4.70 0.01 4.58 0.01 4.78

4I15/2 0.00 0.08 0.00 0.08 0.00 0.09 0.00 0.09 0.00 0.10 0.00 0.11

4I13/2 0.02 1.26 0.02 1.46 0.03 1.64 0.02 1.70 0.03 1.83 0.03 1.88

4I11/2 0.12 4.82 0.14 6.77 0.16 7.58 0.15 7.93 0.16 8.65 0.15 8.47

4I9/2 0.84 27.41 0.82 31.38 0.79 29.09 0.80 33.68 0.79 33.81 0.80 34.45

2H11/2→

4F9/2 0.00 0.11 0.00 0.12 0.00 0.11 0.00 0.13 0.00 0.13 0.00 0.14

4F7/2 0.01 0.33 0.01 0.34 0.01 0.37 0.01 0.39 0.01 0.41 0.01 0.44

4S3/2 0.00 0.04 0.00 0.07 0.00 0.08 0.00 0.09 0.00 0.09 0.00 0.09

4F5/2 0.00 0.07 0.00 0.07 0.00 0.08 0.00 0.09 0.00 0.09 0.00 0.10

2H9/2 0.04 0.85 0.04 0.86 0.04 0.92 0.04 0.98 0.04 1.02 0.04 1.10

4F3/2 0.00 0.03 0.00 0.03 0.00 0.03 0.00 0.03 0.00 0.04 0.00 0.04

4I15/2 0.54 1.13 0.54 1.32 0.50 1.22 0.52 1.42 0.51 1.43 0.51 1.45

4I13/2 0.09 0.12 0.10 0.17 0.11 0.18 0.10 0.19 0.11 0.21 0.10 0.20

4I11/2 0.14 0.15 0.15 0.18 0.16 0.19 0.15 0.21 0.15 0.22 0.15 0.22

4I9/2 0.17 0.14 0.16 0.15 0.18 0.17 0.17 0.18 0.17 0.19 0.18 0.20

4F9/2→

4F7/2 0.00 0.24 0.00 0.27 0.00 0.28 0.00 0.30 0.00 0.31 0.00 0.32

4S3/2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

4F5/2 0.00 0.29 0.00 0.32 0.00 0.35 0.00 0.37 0.00 0.39 0.00 0.41

2H9/2 0.00 0.09 0.00 0.09 0.00 0.08 0.00 0.09 0.00 0.09 0.00 0.10

4F3/2 0.00 0.34 0.00 0.35 0.00 0.39 0.00 0.40 0.00 0.43 0.00 0.46

4I15/2 0.20 5.22 0.22 6.36 0.22 7.14 0.22 7.43 0.23 8.03 0.22 8.15

4I13/2 0.35 5.91 0.35 6.50 0.35 7.30 0.35 7.58 0.35 8.12 0.35 8.48

4I11/2 0.38 4.52 0.35 4.61 0.35 5.19 0.35 5.38 0.35 5.72 0.36 6.12

4I9/2 0.07 0.61 0.07 0.64 0.07 0.72 0.07 0.75 0.06 0.80 0.07 0.85

29

4F5/2→

2H9/2 0.00 0.01 0.00 0.02 0.00 0.02 0.00 0.02 0.00 0.02 0.00 0.02

4F3/2 0.00 0.15 0.00 0.18 0.00 0.17 0.00 0.19 0.00 0.20 0.00 0.20

4I15/2 0.04 2.28 0.04 2.26 0.04 2.55 0.04 2.64 0.04 2.80 0.04 3.02

4I13/2 0.21 6.16 0.20 6.82 0.20 7.67 0.20 7.97 0.20 8.54 0.20 8.90

4I11/2 0.08 1.64 0.11 2.44 0.11 2.72 0.11 2.85 0.11 3.12 0.10 3.02

4I9/2 0.67 9.35 0.66 10.60 0.66 11.92 0.66 12.39 0.66 13.31 0.66 13.77

4F3/2→

4I15/2 0.01 0.35 0.01 0.35 0.01 0.39 0.01 0.40 0.01 0.43 0.01 0.46

4I13/2 0.13 3.62 0.10 3.59 0.11 4.05 0.10 4.19 0.10 4.45 0.11 4.80

4I11/2 0.57 10.14 0.52 10.99 0.52 12.37 0.52 12.84 0.51 13.74 0.53 14.41

4I9/2 0.30 3.73 0.37 5.47 0.37 6.12 0.37 6.41 0.38 7.01 0.36 6.80

30

Table 3.9 : Computed radiative lifetimes τR (µs), computed and experimental branching ratios ( β ) of certain lasing

transitions of Nd3+

doped glasses

BLABIN→

Transition↓ 1 2 3 4 5 6

4F3/2 → τR

cal

βR

cal

βR

exp

τR

cal

βR

cal

βR

exp

τR

cal

βR

cal

βR

exp

τR

cal

βR

cal

βR

exp

τR

cal

βR

cal

βR

exp

τR

cal

βR

cal

βR

exp

4I13/2 2149 0.13 0.02 2161 0.10 0.11 1913 0.11 0.09 1846 0.10 0.12 1735 0.10 0.12 1605 0.11 0.13

4I11/2 404 0.57 0.90 379 0.52 0.74 336 0.52 0.82 323 0.52 0.76 302 0.51 0.77 286 0.53 0.76

4I9/2 283 0.30 0.07 238 0.37 0.15 211 0.37 0.09 203 0.37 0.12 188 0.38 0.11 183 0.36 0.10

31

Table 3.10: Fluorescence peak wavelengths (λP, nm ), effective line widths (Δλeff, nm) and stimulated emission cross

sections (σe, x10

-20cm

2 ) of Nd

3+ in BLABIN glasses

Transition BLABIN→1 2 3 4 5 6

4F3/2 → λP Δλeff σe λP Δλeff σe λP Δλeff σe λP Δλeff σe λP Δλeff σe λP Δλeff σe

4I13/2 1334 51.14 1.20 1331 54.44 1.11 1328 59.24 1.14 1331 56.57 1.25 1330 52.79 1.42 1332 57.74 1.40

4I11/2 1060 5.69 19.51 1063 8.86 13.73 1065 13.17 10.45 1060 33.59 4.18 1065 25.67 5.96 1061 34.65 4.57

4I9/2 900 56.10 0.55 904 54.44 0.84 904 54.30 0.94 907 45.08 1.21 909 41.24 1.45 914 33.60 1.80

3.3.5 Optical band gap

The optical energy band gap and cut-off wavelength were evaluated from the

absorption coefficient (α) near the edge of absorption curve for all the glasses, given by

α = 2.303 A/t where ‘A’ is the absorbance and‘t’ is the thickness of the glass sample in

cm.

The relation between α and photon energy (hν) of the incident radiation is given by [90]

α = B(hν – Eopt )2 / hν …(3.4)

where B is a constant and Eopt is optical energy band gap.

To obtain indirect band gap, (α hν)2 vs hν graph, shown in Fig 3.6(a), is drawn and

the linear region is extrapolated. Direct band gap is obtained by the extrapolation of the

linear region of the plots of (α hν)1/2 vs hν, shown in Fig 3.6(b).

Values of indirect and direct mobility gap and cut-off wavelength for BLABIN:1-6

samples are collected in Table 3.11. Both indirect and direct mobility band gap values

show a maximum for 0.5 mol% and a minimum for 3 mol% concentration of Nd2O3 .

Both the band gaps show the same trend of variation with concentration i.e. 0.1 to 0.5

mol% increase , 0.5 to 1.0 mol% decrease, 1.0 to 1.5 mol% increase and then up to 3.0

mol% decrease is observed, similar to the earlier report [21]. Cut-off wavelength has

opposite trend to both direct and indirect optical band gaps. It is interesting to note that

the variation of optical energy band gap and 2 with Nd3+

ion concentration (Tables3.5

and 3.11) have similar trend. Small increase in Nd2O3 and corresponding small decrease

in B2O3 influence the optical band gap on which switching action depends.

Table 3.11: Optical band gaps and cut-off wavelengths of Nd3+

doped glasses

Parameter BLABIN1 BLABIN2 BLABIN3 BLABIN4 BLABIN5 BLABIN6

Indirect mobility

gap(eV) 3.64 3.68 3.66 3.67 3.65 3.63

Direct mobility gap

(eV) 3.61 3.66 3.62 3.64 3.62 3.61

Cut-off wavelength

(nm) 337 334 336 335 336 338

The variation in optical band gap values can be attributed to similar variation in

the phonon-assisted indirect transition [85]. The decrease in optical band gap at higher

concentrations of Nd2O3 might be due to the increase in the number of non-bridging

oxygen atoms [25]. Lower band gap values indicate the low phonon energies and high

lasing efficiency.

3.3.6 FT-IR spectral analysis

In order to obtain more information about the local structure of the present borate

glasses FT-IR spectra were recorded in the region 4000-400 cm-1

, Fig 3.7. The absorption

peaks in FT-IR spectra can be divided into four main groups in the ranges 3600-2300

cm-1

, 1600-1200 cm-1

, 1200-800 cm-1

and 700-400 cm-1

[87]. The various IR peaks

observed in the glass systems are given in Table 3.12. It is known that boron exhibits

more than one stable configuration. The addition of PbO, Bi2O3 and Al2O3 to the borate

network, changes the boron coordination from three (BO3-) to four (BO4

-) [5]. This

result in the formation of di-, tri-, tetra- and pentaborate groupings, linked together, form

the glass 3D network. The broad bands extending from 3900-3300 cm-1

are due to

hydroxyl groups whose presence may be due to the KBr pellet technique used to record

the IR spectra. The group of bands in the region 1600-1200 cm-1

is due to the asymmetric

stretching relaxation of the B-O bond of trigonal BO3 units, the group of bands in the

region 1200-800cm-1

is due to the B-O bond stretching of the tetrahedral BO4 units and

the other group of bands in the region around 700 cm-1

is due to the bending of B-O-B

linkages in the borate networks [5]. The absence of absorption peak at 806 cm-1

in all the

samples of glasses indicates that there is no boroxol ring formation [87]. This indicates

that the glass structure consists of BO3 and BO4 groups [87-89]. The variation of the

doping concentration of Nd3+

ions result in the structural changes in the 3D glass

network as well as in the local environments of the Nd3+

ions, evident from Fig 3. 7. The

presence of Nd3+

ions seems to influence the surroundings of Bi3+

cations favoring the

formation of BiO6 units [88]. With increasing concentration of Nd3+

ion the vibrations of

BO3 units, Al-O vibrations ~ 1734 cm-1

, Al-O vibrations at ~ 762 cm-1

, BiO6 units due to

Bi-O bend at nearly 580 cm-1

and octahedral units due to Bi-O bend at nearly 473 cm-1

are much affected. The stretching of vibrations at nearly 1048, nearly 1384 nearly 1461

and nearly 1631 cm-1

are unaffected due to increasing concentrations. The stretching

vibrations of network forming oxides result large phonon energies and these effectively

reduce probabilities of radiative processes and luminescent efficiencies of the systems.

Table 3.12: Assignments of FT-IR in Nd3+

doped BLABIN :1-6 glasses

Wavenumber

(cm-1

)

FT- IR assignment

~ 473 Bi-O bend in BiO3 units [36] and stretching vibration in PbO4 [37]

~578 Bi-O bend in BiO6 units [36]

~694 B-O-B angle bending vibrations from pentaborate groups [37]

~762 Al-O vibrations [35]

~1048 BO4 vibrations and stretching vibrations of B-O-Bi linkages [8]

~1384 B-O vibrations various borate rings [8]

~1461 B-O stretching vibrations of BO3 units in chain and ring type

metaborate groups [37]

~1631 Bending modes of OH groups [37], Vibrations of bridging oxygen

atoms between BO3 and BO4 groups [ 38]

~1734 Vibrations of BO3 units [37]

~2330 O-H bond stretching vibrations [8]

~2854 Hydrogen bonding [34]

~2924 Hydrogen bonding [34]

~3437 Characteristic stretching of OH- groups [34]

~3852 Characteristic stretching of OH- groups[34]

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0

0.0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100.0

cm-1

%T

NDC1

3437

2924

2854

2330

1734

1631

1461

1384

1048

784

762

694

578

473

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0

0.0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100.0

cm-1

%T

NDC2

3432

2924

2853

2321

1629

1462

1382 1044

719

588

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0

0.0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100.0

cm-1

%T

NDC33852

3436

2924

2854

2332

1457

1384 1049

690

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0

0.0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100.0

cm-1

%T

NDC4

3428

2923

2853

2334

1628

1508

1460

1377

1048

721

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0

0.0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100.0

cm-1

%T

NDC6

34392924

2854

2322

1626

1456

1383

1053

684

494

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400.0

0.0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100.0

cm-1

%T

NDC5

3438 2924

2853

2345

1461

1384

1046

686

Fig . 3.7. FT-IR spectra of BLABIN : 1-6 (NDC:1-6) glasses.

3.4. CONCLUSIONS

The Nd3+

doped heavy metal oxide lead-bismuth-aluminum-borate glasses have

been fabricated and characterized for their lasing potencies. The numerical aperture is

0.25 for all the glasses indicating these are potential candidates for core material of

optical fiber. The low rms deviation values obtained in the fitting analysis for

experimental and calculated band positions support the validity of the evaluated

spectroscopic parameters. The Slater integrals F2/F

4 and F

2/F

6 are in agreement with the

other reported works. The bonding observed in the glasses is of covalent in nature. The

spectroscopic quality factor χ less than unity indicates these glasses are good lasing

candidates. Ω4 and Ω6 values indicate that the rigidity of the present glasses under study

increases with increasing concentration. BLABIN:1 glass has χ = 0.38 equivalent to

that of Nd:YAG laser indicating it as a good lasing material. The values of branching

ratios (R) and emission cross sections (e) obtained for all the glasses are of high in

magnitude for the lasing transition 4

F3/24I11/2 indicating the investigated glasses may

be good laser hosts. The indirect and direct mobility gap values show a maximum for 0.5

mol% and minimum for 3.0 mol% concentration and decreasing trend from 1.5 to 3.0

mol% of Nd2O3, indicating the decrease in the phonon energy and hence increase in

lasing efficiency with increase of concentration. Hence these glasses have good switching

action and lasing potencies.

The structural changes in the 3D glass network as well as in the local

environments of the Nd3+

ions take place due to the variation of the doping concentration

of Nd3+

ions, evident from FT-IR spectra. The coexistence of trigonal BO3 and

tetrahedral BO4 units was evidenced by FT-IR spectroscopy and the increase of PbO

content to the glass matrix promotes the conversion of some BO3 units to BO4.