SPECTRAL PROPERTIES OF Pr3+ IONS DOPED IN LEAD BISMUTH ...shodhganga.inflibnet.ac.in/bitstream/10603/10071/9/chapter- 6.pdf · BISMUTH–ALUMINUM-BORATE GLASSES WITH HOST VARIATION.

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CHAPTER 6

SPECTRAL PROPERTIES OF Pr3+

IONS DOPED IN LEAD–

BISMUTH–ALUMINUM-BORATE GLASSES WITH HOST

VARIATION.

ABSTRACT

________________________________________________________________________

The effect of the increase in PbO content and decrease in B2O3 content on the

physical and spectroscopic properties of lead–bismuth–aluminum-borate glasses have

been studied for the compositions: (x-0.5) PbO + (90-x) B2O3 + 5 Bi2O3 + 5Al2O3 +

0.5Pr6 O11 where x = 10, 15, 20, 25 and 30 mol%. Various spectroscopic parameters

have been computed from the room temperature absorption spectra. The Judd-Ofelt

intensity parameters Ωλ ( λ = 2,4,6) 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

transitions 3

P0 3H4,

3P1

3H5,

1D2

3H4 and

3P0

3F2 were evaluated from

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

recorded and analyzed.

2

6.1 INTRODUCTION

Recently heavy metal oxide (HMO) glasses based on cations such as PbO, B2O3,

Bi2O3 having high value of atomic weight have attracted the interest for research because

of their different important optical properties. Praseodymium doped glasses find variety

of practical applications such as solid lasers [71], fiber amplifiers in 1.3 μm region [129],

optical fibers [128], up- converters [127]. Laser action in visible spectral region has been

observed for the transition 1D2→

3H4 of the Pr

3+ ion [135]. Laser transition

1G4→

3H5

observed at ~1.3 μm in Pr3+

doped glass fibers has been found to be very promising

transition for developing fiber amplifier for communication in the second telecom

window [129]. The optical properties of laser glasses are influenced by the ligand field of

rare earth ion environment. When the glasses are activated with rare earth ions they offer

a variety of dopant sites with strong ion-host interactions [144].The enhanced band width

makes rare earth doped glasses as tunable and ultra-fast laser medium. Phosphate glasses

are hygroscopic. Borate glasses have low phonon energy losses, excellent physical and

chemical properties like high density high refractive index and high stability. Trivalent

praseodymium is an excellent optical activator which offers the possibility of

simultaneous blue, green and red emission for laser action. It is possible to have infrared

emission for optical amplification at 1.3 μm . Pr3+

ions doped glasses are also useful as

short wave length up-conversion laser materials [144] moreover, among the rare earths,

trivalent praseodymium ions (Pr3+

) are potential for laser applications due to a large

number of available energy levels in the UV, visible and near infrared regions.

In the present work the standard Judd-Ofelt theory [51,52] has been used to analyze

the absorption spectra of Pr3+

ions in different glass matrices. It is well known that J-O

3

theory fails particularly in the case of Pr3+

ions due to the small energy gap between the

ground state configuration 4f2

and the first excited state 4f 5d [59] to solve this problem

used the standard J-O theory in the case of Pr3+

doped fluorozirconate glasses. Due to the

hyper-sensitive transition of 3H4

3P2 the difference between the experimental and

calculated values of the oscillator strengths is more. Intensity parameters Ω2, Ω4 and Ω6

[59] were determined by least square fit method and so the difference between the

experimental and calculated values of the oscillator strengths is made minimum. These

three parameters are used to calculate Racha, Slator- Condan, spin-orbit coupling,

configuration interaction parameters were computed. Spectroscopic parameters such as

electric dipole strength, radiative transition probabilities, lifetimes, branching ratios and

integrated absorption cross-section were evaluated. The effect of compositional changes

of the glasses on the optical properties of Pr3+

ions has been discussed.

Special attention was given to lasing transitions and compared the βR values for Pr3+

ion in different glass environments.

6.2 EXPERIMENTAL

Heavy metal oxide glasses with the molar composition of (x-0.5) PbO + (90-x) B2O3 +

5 Bi2O3 + 5Al2O3 + 0.5 Pr6 O11 with x=10, 15, 20, 25 and 30 mol% were prepared and

designated as BIPLAB:1,2,3,4 and 5 respectively. 10g batch chemical compositions

were weighted more accurately, mixed and grinded in an agate mortar and then

compositions were taken in silica porcelain crucible kept at 400oC for 30 min and melted

in an electric furnace in the temperature range of 950-1000 o

C for 1 hour. The melt is

then poured on to a preheated brass plate and air quenched to get a good optical quality

4

glasses. The samples are annealed at about 400oC for 5 hours to remove thermal strains

and then polished before measuring their optical properties.

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

.

Refractive indices (n) were evaluated using conventional methods. Densities were

measured by the Archimedes method using Xylene as an immersion liquid. XRD spectra

were recorded for five samples with different chemical compositions to confirm their

amorphous nature.

6.3 RESULTS AND DISCUSSION

6.3.1 Physical properties

Using relevant equations 2.1 to 2.12 given in chapter 2, the physical properties were

obtained and collected in Table 6.1. With increase of PbO content and decrease of B2O3

content refractive index (n), density (d),average molecular weight, optical dielectric

constant (ε), reflection losses, electric susceptibility 𝝌𝒆 and numerical aperture (NA)

increases; Pr3+

ion concentration, molar refractivity , inter-ionic distance (ri), polaron

radius (rp), field strength (F) change disorderly and Molecular volume (VM) decreases.

NA range from 0.23 to 0.26 indicating the suitability of the material as core material for

5

optical fibers. It is interesting to note that the refractive indices of the glasses under study

increases gradually with the increase of PbO and the decrease of B2O3 content. The

higher magnitude refractive indices of all the five glasses make them to fit as the lasing

candidates and core materials of the optical fiber.

Table 6.1: Various physical properties of Pr3+

: BIPLAB 1-5 glasses

S.No. Parameter BIPLAB 1 BIPLAB 2 BIPLAB 3 BIPLAB 4 BIPLAB

5

1 Refractive index, n 1.616 1.676 1.736 1.796 1.856

2 Density d (gm/cm3) 3.265 3.586 3.851 3.913 4.002

3 Average molecular

weight (g)

196.61 202.86 208.34 213.24 217.56

4 Molecular volume

(VM) (cm3)

60.22 56.57 54.10 54.50 54.36

5 Optical path

length(cm)

0.294 0.292 0.300 0.292 0.292

6 Pr3+

conc.(1020

ions

/cc)

2.705 2.772 2.798 2.682 2.598

7 Optical dielectric

constant, ε

2.612 2.809 3.014 3.226 3.445

8 Reflection loss R (%) 5.545 6.381 7.236 8.105 8.983

9 Molar refractivity Rµ

(cm3)

24.442 24.384 24.630 26.067 27.192

10 Inter-ionic distance ri

(Å)

15.501 15.750 15.850 15.416 15.091

11 Polaron radius rP (Å) 7.177 7.119 7.097 7.197 7.274

12 Field strength F (10+15

cm-2

)

2.892 2.869 2.860 2.900 2.931

13 Electric susceptibility

(χe)

0.128 0.144 0.160 0.177 0.195

14 Numerical aperture

(NA)

0.23 0.24 0.25 0.25 0.26

6

6.3.2 Optical absorption spectra

The optical absorption spectra of Pr3+

doped BIPLAB glasses obtained at room

temperature are shown in Fig 6.1(a) (UV-VIS) and Fig 6.1(b) (NIR). The absorption

spectra observed experimentally for Pr3+

: BIPLAB glasses shown in Figs 6.1(a) and (b)

are similar to the spectra observed for Pr3+

: glasses [141,145].

Fig. 6.1 (a) Optical absorption spectra (visible) of Pr3+

: BIPLAB glasses

7

.

Fig. 6.1 (b) Optical absorption spectra (NIR) of Pr3+:

BIPLAB glasses

In these figures all the bands which originate from the ground state 3H4 to various

excited levels are assigned [141,145]. In the absorption spectra only 7 excited states are

observed out of 12 of Pr3+

ion. The transitions which are not observed are 1s0, too high in

energy, 1I6 spin- forbidden and masked by the intense spin- allowed transitions of

3H4

3P0, 1, 2,

3H5 too low in energy in NIR and

3F2 due to instrument limitations.

The observed transitions in the spectral region of 400-900 nm are: a group of three

overlapping bands corresponding to 3H4

3P0,1,2 transitions, an isolated band

corresponding to 3H4

1D2 in the visible region, the weak band corresponding to

3H4

1G4 and two overlapping bands

3H4

3F4 ,

3F3 in the near infrared region (NIR). The

observed and calculated energies in cm-1

are given in Table 6.2. The rms deviation range

from 14.62 to 18.838, in good agreement with the literature [141]. For the transition

8

3H4

1D2 blue shift is observed for all the glass samples. The spectroscopic parameters

are collected in Table 6.3. In this table two body electrostatic repulsion parameters F2

, F4

and F6

, spin-orbit parameter ξ, two body interaction parameters α and β and bonding

parameter δ are also given. The sum of Slater parameter, 𝚺FK, indicates the net

electrostatic interaction experienced by Pr3+

ions in the host matrix. The positive value of

bonding parameter δ indicates that the bonds between Pr3+

ion and ligands are covalent in

nature.

6.3.3 Judd-Ofelt intensity analysis

The experimental oscillator strengths of the absorption bands of Pr3+

BIPLAB glasses

are determined from absorption spectra and are given in Table 6.4 along with calculated

oscillator strengths. The change in fexp values is non uniform except in

3H4

3F3

transition in which almost uniform increase is observed. This is probably due to the

increase and decrease in the site- symmetry of the Pr3+

ion with increase in PbO and

decrease in B2O3 contents. Also some uncertainty is associated with weak spectra and

overlapping spectra in determining the oscillator strengths.

The reduced matrix elements used in the present JO analysis are taken from literature

[17] as they are almost independent on the host. Standard JO analysis and least square

fit is used in finding JO parameters. The inclusion of 3

P2 may give negative Ω2 for Pr

3+

ion because it is hyper- sensitive. By the exclusion of 3P2 transitions Ωλ values are

calculated and obtained positive values. Ωλ (λ=2,4 and 6) are given in Table 6.5. It is

observed that Ω6 > Ω4 > Ω2 for BIPLAB:1,2 and 4 glasses and Ω4 > Ω6 > Ω2 for

9

Table 6.2 : Experimental and calculated energies of Pr3+

: BIPLAB 1-5 glasses

BIPLAB:3 and 5 glasses. The parameter Ω2 is associated with asymmetry of the

ligand field near the rare earth ion. Ω2 value are in the order BIPLAB:1 > BIPLAB:5 >

BIPLAB:3 > BIPLAB:2 > BIPLAB:4. The higher values of Ω2 obtained for BIPLAB:1,

3 and 5 glasses in the present study indicate that the asymmetry and covalence of the

ligand field at the rare earth site are higher as expected from bonding parameter.

Transition

from

3H4 to

BIPLAB1

BIPLAB2

BIPLAB3

BIPLAB4

BIPLAB5

E

exp

E

cal

E

exp

E

cal

E

exp

E

cal

E

exp

E

cal

E

exp

E

cal

3P2 22523 22550 22523 22536 22523 22539 22573 22602 22573 22585

3P1 21322 21285 21322 21305 21322 21300 21322 21282 21322 21306

3P0 20747 20760 20747 20753 20747 20755 20747 20761 20747 20753

1D2 16932 16929 16949 16948 16920 16918 16920 16917 16978 16977

1G4 9990 9973 9930 9922 9930 9920 9930 9911 9980 9972

3F4 6958 7005 6983 7005 6978 7006 6920 6972 7003 7024

3F3 6579 6549 6553 6539 6570 6552 6618 6584 6591 6577

rms

deviation

± 28 ±14 ± 17 ± 31 ± 13

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Table 6.3 : Spectroscopic parameters of Pr3+

: BIPLAB 1-5 glasses

The spectroscopic quality factor Ω4/Ω6 observed range from 0.954 to 1.047 indicating

that these glasses are fairly rigid as compared to other glasses reported in literature [146].

Thus the obtained J-O parameters indicate that the present glasses are more potential

lasing candidates.

Parameter BIPLAB 1 BIPLAB BIPLAB BIPLAB4 BIPLAB 5

E1(cm-1) 6175.953 5535.883 5698.997 6663.452 5837.79

E2(cm-1) 26.22571 23.94897 24.57818 28.61521 25.20705

E3(cm-1) 551.3884 507.5294 519.6103 589.3428 528.6952

ξ4f (cm-1) 757.6454 745.096 749.0585 781.0701 764.072

α (cm-1) 142.6695 74.80655 93.54772 202.5098 108.6355

β (cm-1) -4063.96 -2468.15 -2926.12 -5451.39 -3264.14

F2 (cm-1) 380.7501 346.2716 355.4617 410.4333 363.2868

F4(cm-1) 64.57357 57.82642 59.51007 68.84215 60.72278

F6 (cm-1) 406.2958 373.2545 382.348 434.6994 389.0044

F2 (cm-1) 85668.77 77911.12 79978.87 92347.49 81739.53

F4 (cm-1) 70320.62 62972.97 64806.46 74969.1 66127.11

F6 (cm-1) 2991003 2747765 2814708 3200100 2863710

F2 / F4 1.21826 1.237215 1.234119 1.231807 1.236097

F2 / F6 0.028642 0.028354 0.028415 0.028858 0.028543

Σ FK 3146993 2888649 2959494 3367417 3011577

δ 0.007454 0.007876 0.008039 0.007655 0.006084

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Table 6.4 : Experimental and calculated oscillator strengths( x 10-6) and rms

deviation Pr3+ : BIPLAB: 1-5 glasses.

Level

BIPLAB 1 BIPLAB 2 BIPLAB 3 BIPLAB 4 BIPLAB 5

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

3P2 13.549 6.212 14.243 6.555 14.705 6.987 15.497 8.040 15.652 8.082

3P1 4.852 5.753 5.549 5.941 6.806 6.820 7.872 7.548 8.202 7.762

3P0 4.140 5.664 3.717 5.849 4.201 6.713 4.690 7.430 4.751 7.641

1D2 2.634 1.941 2.819 2.006 3.094 2.161 3.067 2.455 3.206 2.516

1G4 0.368 0.557 0.393 0.579 0.484 0.620 0.538 0.708 0.549 0.721

3F4 5.083 6.196 5.274 6.444 5.654 6.833 6.705 7.834 6.822 7.970

3F3 11.862 11.57 12.11 11.80 13.20 12.89 14.81 14.51 15.33 15.03

rms

deviation

with 3P2

± 2.898 ± 3.070 ± 3.123 ± 3.066 ± 3.111

without 3P2 ± 0.843 ± 0.989 ± 1.114 ± 1.161 ±1.223

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Table 6.5 : Judd-Ofelt intensity parameters (Ωλ,λ=2,4,6)(x10-20

cm2) Pr

3+:

BIPLAB: 1-5 glasses.

To evaluate the emission properties of the present glass systems the J-O intensity

parameters that are determined by excluding the transition 3H4

3P2 have been taken into

consideration. Electric dipole line strengths (S’ed) and radiative transition probabilities

(AR) of certain lasing transitions of Pr3+

doped glasses are given in Table 6.6. The

changes in the line profiles indicate small change in the concentration of Pr3+

changes the

network structure of the glass and the local environment of the optically active ion.

BIPLAB →

Parameter ↓ 1 2 3 4 5

Ω2 7.64 3.49 5.17 2.99 7.04

Ω4 8.34 8.61 9.42 9.93 9.72

Ω6 8.51 9.03 8.99 9.96 9.47

Ω4/ Ω6 0.98 0.954 1.047 0.997 1.026

Ω2 + Ω4 + Ω6 25.47 21.1 23.6 22.9 26.2

13

Table 6.6 : Electric dipole line strengths (S’ed cm2x10

-20) and radiative transition

probabilities A (s-1

) of certain lasing transitions of Pr3+

: BIPLAB 1-5 glasses

Transition BIPLAB 1 BIPLAB 2 BIPLAB 3 BIPLAB 4 BIPLAB 5

S’ed A S’ed A S’ed A S’ed A S’ed A 3P2

1I6 1.559 1 1.508 1 1.663 2 1.829 2 1.747 2

3P1 3.186 3 1.455 2 2.156 3 1.247 2 2.936 5

3P0 1.457 4 0.666 2 0.986 4 0.570 2 1.343 6

1D2 0.657 63 0.285 31 0.739 90 0.776 106 0.764 117

1G4 5.682 6233 2.679 3315 4.073 5674 2.643 4138 5.357 9408

3F4 4.098 8527 1.904 4467 3.201 8456 2.367 7030 4.006 13343

3F3 6.964 15571 4.605 11615 6.802 19314 6.682 21322 7.510 26887

3F2 5.173 14879 3.809 12356 5.552 20280 5.917 24289 5.839 26892

3H6 4.584 15488 2.272 8656 5.145 22071 5.449 26273 5.319 28771

3H5 2.699 12755 1.876 9998 2.966 17801 3.191 21520 3.086 23353

3H4 1.432 9037 1.334 9495 1.535 12296 1.682 15148 1.609 16258

1I6

3P1 0.003 0 0.004 0 0.004 0 0.004 0 0.004 0

3P0 0.026 0 0.027 0 0.027 0 0.030 0 0.028 0

1D2 13.760 257 13.334 281 14.683 348 16.145 430 15.418 461

1G4 19.104 6071 11.901 4266 20.325 8202 21.155 9594 21.514 10946

3F4 9.624 6139 6.478 4661 10.296 8340 10.843 9871 10.858 11089

3F3 0.030 20 0.026 20 0.032 28 0.035 34 0.033 37

3F2 0.329 297 0.321 327 0.351 403 0.386 498 0.369 533

3H6 0.179 192 0.103 124 0.187 254 0.190 291 0.200 343

3H5 0.024 37 0.021 36 0.025 49 0.027 59 0.027 66

3H4 0.673 1399 0.414 972 0.715 1889 0.743 2205 0.758 2522

3P1

3P0 0.000 0 0.000 0 0.000 0 0.000 0 0.000 0

1D2 6.742 517 3.080 266 4.563 444 2.639 288 6.213 762

1G4 0.703 948 0.304 463 0.794 1360 0.837 1611 0.819 1769

3F4 2.186 5942 0.946 2901 2.469 8522 2.603 10097 2.548 11088

3F3 6.003 17644 2.703 8961 4.804 17930 3.659 15346 5.932 27912

3F2 2.050 7905 0.936 4073 1.387 6793 0.802 4415 1.889 11663

3H6 1.060 4860 1.125 5816 1.120 6519 1.241 8117 1.180 8659

3H5 3.143 20608 1.838 13592 3.494 29094 3.726 34872 3.623 38034

3H4 1.429 12733 0.619 6216 1.615 18263 1.702 21636 1.666 23760

3P0

1D2 0.113 17 0.052 9 0.077 15 0.044 10 0.104 26

1G4 0.466 1626 0.202 794 0.527 2332 0.555 2762 0.543 3033

3F4 0.897 6505 0.388 3176 1.013 9329 1.067 11053 1.045 12138

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6.3.4 Radiative parameters

In Fig.6.2 the emission spectra of BIPLAB:1-5 glasses obtained in the wavelength range

450-700 nm upon excitation at 445 nm wavelength of xenon flash lamp are shown. The

assignment of emission band positions have been made based on literature [141,142] and

are attributed to 3P0

3H4 ,

3P1

3H5 ,

1D2

3H4 and

3P0

3F2 transitions. The emission

3F3 0.000 0 0.000 0 0.000 0 0.000 0 0.000 0

3F2 2.255 23513 1.030 12114 1.526 20205 0.882 13132 2.078 34689

3H6 0.618 7702 0.656 9218 0.653 10332 0.723 12865 0.688 13723

3H5 0.000 0 0.000 0 0.000 0 0.000 0 0.000 0

3H4 1.434 35429 0.621 17296 1.619 50814 1.707 60201 1.671 66110

1D2

1G4 3.323 627 1.899 404 2.691 645 2.150 579 3.292 995

3F4 4.814 2643 2.302 1426 3.323 2317 2.017 1581 4.469 3929

3F3 0.410 251 0.183 127 0.348 271 0.285 250 0.415 408

3F2 0.853 765 0.372 376 0.914 1041 0.928 1188 0.967 1390

3H6 0.652 739 0.319 408 0.732 1054 0.775 1254 0.756 1373

3H5 0.022 40 0.012 24 0.024 56 0.026 67 0.025 73

3H4 0.627 1685 0.561 1699 0.667 2277 0.724 2776 0.703 3023

1G4

3F4 4.257 35 3.722 34 4.563 48 4.960 58 4.790 63

3F3 0.514 6 0.495 7 0.534 8 0.578 10 0.568 11

3F2 0.183 6 0.113 4 0.202 9 0.216 10 0.210 11

3H6 6.202 356 4.031 261 5.961 434 5.765 472 6.638 610

3H5 4.666 702 4.255 722 4.881 932 5.254 1128 5.181 1248

3H4 0.287 87 0.262 90 0.304 117 0.330 142 0.321 155

3F4

3F3 5988.362 99 2592.121 49 6763.743 143 7129.875 169 6979.193 186

3F2 0.790 1 0.822 2 0.830 2 0.914 2 0.877 2

3H6 13.355 83 8.347 59 12.835 102 12.356 110 14.300 143

3H5 6.607 238 5.248 213 7.081 323 7.606 390 7.445 429

3H4 4.664 483 4.602 538 4.905 645 5.360 792 5.186 860

3F3

3F2 0.585 1 0.257 0 0.588 1 0.569 1 0.643 1

3H6 9.852 50 8.787 51 10.602 69 11.585 85 11.104 91

3H5 7.695 280 3.446 141 6.517 301 5.323 276 7.796 454

3H4 9.347 1053 7.794 990 9.896 1415 10.608 1705 10.458 1886

15

bands corresponding to 3P0

3H4 and

1D2

3H4 transitions are more intense compared

the other two transitions. The emission band of the transition 3P1

3H5 has been almost

merged with that of 3P0

3H4 transition.

For all the five BIPLAB glasses doped with Pr3+

ions, Table 6.7 gives radiative

lifetimes (זR ) and Table 6.8 gives branching ratios (βR ) and integrated absorption cross-

sections (ζa) for certain important transitions. Computed radiative life times for these

transitions are in the order 3F4>

1G4 >

1D2 >

1I6 >

3P1 >

3P0 >

3P2. Higher life times

comparative to others’ indicate better lasing transitions. It is observed that the branching

ratios of the following transitions exhibit higher values.

16

3P1

3F3

3P0

3F2

iD2

3F4

1G4

3H5 ,

3H6

Table 6.7 : Computed radiative lifetimes τR (µs) of certain lasing levels of Pr3+

:

BIPLAB 1-5 glasses

Table 6. 8 : Branching ratios ( β) and integrated absorption cross sections (σa x 1018

cm-1

) of certain lasing transitions of Pr3+

: BIPLAB 1-5 glasses.

Lasing level BIPLAB 1 BIPLAB 2 BIPLAB 3 BIPLAB 4 BIPLAB 5

3P2 12 17 9 8 7

1I6 69 94 51 44 38

3P1 14 24 11 10 8

3P0 13 23 11 10 8

1D2 148 224 131 130 89

1G4 839 895 646 549 477

3F4 1105 1164 823 683 617

Transitio

n

BIPLAB 1

BIPLAB 2

BIPLAB 3

BIPLAB 4

BIPLAB 5

β σa β σa β σa β σa β σa 3P2

1I6 0.000 0.496 0.000 0.503 0.000 0.583 0.000 0.673 0.000 0.675

3P1 0.000 1.086 0.000 0.520 0.000 0.809 0.000 0.491 0.000 1.215

3P0 0.000 0.721 0.000 0.345 0.000 0.537 0.000 0.326 0.000 0.807

1D2 0.001 1.030 0.001 0.468 0.001 1.274 0.001 1.405 0.001 1.454

1G4 0.075 20.073 0.055 9.924 0.054 15.833 0.035 10.788 0.065 22.969

3F4 0.103 17.921 0.075 8.729 0.080 15.400 0.059 11.961 0.092 21.259

17

3F3 0.189 31.190 0.194 21.630 0.182 33.524 0.178 34.578 0.185 40.830

3F2 0.180 25.198 0.206 19.454 0.191 29.760 0.203 33.301 0.185 34.525

3H6 0.188 23.562 0.144 12.242 0.208 29.096 0.219 32.359 0.198 33.182

3H5 0.154 15.513 0.167 11.304 0.168 18.760 0.180 21.190 0.161 21.532

3H4 0.109 9.065 0.158 8.855 0.116 10.688 0.126 12.302 0.112 12.364

1I6

3P1 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

3P0 0.000 0.002 0.000 0.002 0.000 0.002 0.000 0.002 0.000 0.002

1D2 0.018 6.612 0.026 6.719 0.018 7.764 0.019 8.964 0.018 8.993

1G4 0.421 23.617 0.399 15.427 0.420 27.647 0.417 30.216 0.421 32.281

3F4 0.426 15.007 0.436 10.593 0.427 17.667 0.430 19.537 0.427 20.552

3F3 0.001 0.047 0.002 0.044 0.001 0.056 0.001 0.064 0.001 0.065

3F2 0.021 0.577 0.031 0.589 0.021 0.677 0.022 0.782 0.021 0.784

3H6 0.013 0.332 0.012 0.200 0.013 0.381 0.013 0.407 0.013 0.450

3H5 0.003 0.051 0.003 0.045 0.003 0.058 0.003 0.065 0.003 0.068

3H4 0.097 1.556 0.091 1.005 0.097 1.820 0.096 1.985 0.097 2.127

3P1

3P0 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

1D2 0.007 13.788 0.006 6.604 0.005 10.266 0.003 6.235 0.006 15.421

1G4 0.013 3.740 0.011 1.697 0.015 4.648 0.017 5.145 0.014 5.290

3F4 0.084 14.689 0.069 6.667 0.096 18.256 0.105 20.207 0.090 20.779

3F3 0.248 41.406 0.212 19.549 0.202 36.460 0.159 29.156 0.226 49.657

3F2 0.111 15.478 0.096 7.414 0.076 11.525 0.046 6.999 0.094 17.311

3H6 0.068 8.481 0.138 9.436 0.073 9.858 0.084 11.468 0.070 11.455

3H5 0.290 28.323 0.321 17.367 0.327 34.650 0.362 38.803 0.308 39.628

3H4 0.179 14.268 0.147 6.476 0.205 17.733 0.224 19.628 0.192 20.183

3P0

1D2 0.000 0.607 0.000 0.291 0.000 0.452 0.000 0.274 0.000 0.678

1G4 0.022 7.080 0.019 3.214 0.025 8.800 0.028 9.740 0.023 10.016

3F4 0.087 17.383 0.075 7.890 0.100 21.605 0.111 23.914 0.094 24.591

18

3F3 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

3F2 0.314 49.334 0.284 23.631 0.217 36.735 0.131 22.308 0.267 55.178

3H6 0.103 14.348 0.216 15.964 0.111 16.678 0.129 19.402 0.106 19.380

3H5 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

3H4 0.474 41.823 0.406 18.983 0.546 51.980 0.602 57.536 0.510 59.164

1D2

1G4 0.093 6.529 0.091 3.911 0.084 5.816 0.075 4.881 0.089 7.850

3F4 0.392 13.503 0.319 6.772 0.302 10.255 0.205 6.537 0.351 15.213

3F3 0.037 1.192 0.028 0.560 0.035 1.114 0.032 0.959 0.036 1.468

3F2 0.113 2.818 0.084 1.288 0.136 3.322 0.154 3.541 0.124 3.879

3H6 0.109 2.328 0.091 1.195 0.138 2.876 0.163 3.197 0.123 3.279

3H5 0.006 0.091 0.005 0.051 0.007 0.112 0.009 0.125 0.007 0.128

3H4 0.250 2.987 0.381 2.799 0.297 3.497 0.361 3.984 0.270 4.062

1G4

3F4 0.029 1.987 0.031 1.822 0.031 2.344 0.032 2.675 0.030 2.714

3F3 0.005 0.270 0.006 0.273 0.005 0.309 0.005 0.351 0.005 0.363

3F2 0.005 0.136 0.004 0.088 0.006 0.166 0.006 0.186 0.005 0.190

3H6 0.299 5.538 0.233 3.774 0.281 5.856 0.259 5.948 0.291 7.194

3H5 0.589 5.744 0.646 5.493 0.602 6.611 0.619 7.473 0.595 7.741

3H4 0.073 0.446 0.080 0.428 0.075 0.520 0.078 0.593 0.074 0.605

3F4

3F3 0.110 353.654 0.056 160.518 0.117 439.531 0.115 486.504 0.115 500.284

3F2 0.001 0.219 0.002 0.239 0.001 0.253 0.002 0.293 0.001 0.295

3H6 0.092 5.690 0.068 3.729 0.084 6.017 0.075 6.083 0.088 7.395

3H5 0.263 5.049 0.248 4.205 0.266 5.954 0.267 6.715 0.265 6.905

3H4 0.534 5.070 0.626 5.246 0.531 5.868 0.541 6.732 0.531 6.843

3F3

3F2 0.000 0.164 0.000 0.076 0.000 0.181 0.000 0.184 0.000 0.219

3H6 0.036 4.649 0.043 4.348 0.039 5.505 0.041 6.316 0.037 6.359

3H5 0.202 6.976 0.119 3.275 0.168 6.501 0.134 5.576 0.187 8.579

3H4 0.761 12.354 0.837 10.802 0.793 14.392 0.825 16.200 0.776 16.778

19

An important lasing transition for optical fiber is 1G4

3H5. In the present glasses this

transition exhibits high values of branching ratios. This property is observed for ZBLN,

(Ge S2 )80 (Ge

2 S3) 20 and Ga-La-S fluoride and sulfide glasses for optical fibers [147].

In order to predict the luminescence characteristics of Pr3+

ion in the present glass

matrices, the radiative parameters such as emission peak wavelengths( λp), effective line

widths (Δλeff) and stimulated emission cross-sections (ζe) are presented in Table 6.9. The

observed band positions of 3P0

3H4 transition are 492, 491, 492, 495 and 494 nm, of

1D2

3H4 transition are 602, 604, 604, 604 and 603 nm and those of

3P0

3F2 transition

are 645, 645, 646, 645 and 645 nm for BIPLAB: 1-5 glasses. For 3P1

3H5 transition,

524, 527, 523, and 524 nm are the band positions observed for BIPLAB: 1-4 glasses and

no band was observed for BIPLAB: 5 glass. The red shift may be attributed to the site

distribution of Pr3+

ions in the vicinity of ligand fields [141,143].

The values of ζe for 3P0

3H4 transition are in the order BIPLAB:3 > BIPLAB:5>

BIPLAB:1> BIPLAB:4> BIPLAB:2 and for 1D2

3H4 transition are in the order

BIPLAB:3> BIPLAB:5> BIPLAB:1> BIPLAB:4> BIPLAB:2. The high values of

emission cross-sections indicate that these glass matrices are good laser active media

indicating the increase in the gain parameter. Application of J-O theory to Pr3+

ion in

analyzing the radiative parameters yield poor agreement between calculated and

experimental values due to the strong f-d mixing which is not accounted by the theory.

20

Table 6.9: Emission peak wavelengths (λP, nm ), effective line widths (Δλeff, nm) and stimulated emission

cross sections (σe, x10

-20cm

2 ) of Pr

3+ doped glasses

Transition

BIPLAB 1 BIPLAB 2 BIPLAB 3 BIPLAB 4 BIPLAB 5

λP Δλeff σe λP Δλeff σe λP Δλeff σe λP Δλeff σe λP Δλeff σe

3P0→

3H4 492 20.270 5.20 491 17.568 2.703 492 18.919 6.930 495 29.730 5.001 494 24.324 6.235

3P1→

3H5 524 - - 527 - - 523 - - 524 - - - - -

1D2→

3H4 602 22.973 0.490 604 25.000 0.427 604 23.649 0.564 604 25.676 0.592 603 27.027 0.570

3P0→

3F2

645 - - 645 - - 648 - - 645 - - 645 - -

21

6.3.5 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 given by α=2.303 A/t where ‘A’ is absorbance

and ‘t’ is thickness of the glass sample. The relation between α and photon energy (hν) of the

incident radiation is given by [85] α=B (hν-Eopt )2

/ hν where B is the constant and Eopt is the

optical energy band gap. To obtain indirect band gap (αhν)2

vs hν graph is drawn and

extrapolated the linear region, Fig.6.3(a).

22

Direct band gap is obtained by the extrapolation of the linear region of the plots of (αhν)1/2

vs hν,

Fig.6.3(b).

Values of indirect and direct mobility gap and cut-off wavelength for BIPLAB:1-5 samples

are collected in Table 6.10. Both indirect and direct mobility gap values show a non-uniform

variation with increase of PbO content and decrease of B2O3 content [86] indicating variation of

switching action, which might be due to the increase in the number of non-bridging oxygen

23

atoms. The decrease in the values of optical band gap energy can thus be attributed to decrease in

the phonon- assistant indirect transitions [86]. Cut-off wavelength has opposite trend to both

direct and indirect optical band gaps as expected and show a red shift.

Table 6.10: Optical band gap and cut-off wavelength of Pr3+

doped BIPLAB: 1-5 glasses

Parameter BIPLAB 1 BIPLAB 2 BIPLAB 3 BIPLAB 4 BIPLAB 5

Indirect mobility

gap(eV)

3.72 3.59 3.53 3.59 3.59

Direct mobility gap

(eV)

3.68 3.53 3.48 3.56 3.56

Cut-off wavelength

(nm)

339 344 352 354 361

6.4 FT-IR spectra

FT- IR spectra were recorded for all the glass samples BIPLAB: 1-5, Fig.6.4, and

assignments were made and collected in Table 6.11. A band from ~ 493 cm-1

was ascribed to the

Bi-O bend in Bi O3 units [106] and stretching vibration in Pb O4[107]. A band from ~687 to

~820 cm-1

was attributed to the B-O-B angle bending vibrations from pentaborate groups [107].

A band from ~761 to ~768 cm-1

was ascribed to the Al-O vibrations [105]. A band from ~816

cm-1

was attributed to the Boroxal ring [124]. A band from ~952 is due to the B-O stretching of

BO4 units from diborate groups [5] and Pb-O symmetrical stretching vibrations [121]. A band

from ~973 cm-1

was attributed to the B-O stretching of BO4 units from diborate groups [5,89] and

Pb-O symmetrical stretching vibrations [121]. A band from ~1044 to ~1048 cm-1

corresponds to

24

the BO4 vibrations and stretching vibrations of B-O-Bi linkages [25]. A band from ~ 1214 cm-1

was attributed to the B-O- symmetric stretch in BO3 units from pyro-and ortho –borate groups

[89] .A band from ~1377 cm-1

was ascribed to the B-O vibrations of various borate rings [25]. A

band from ~1457 cm-1

was attributed to the B-O stretching vibrations of BO3 units in chain and

ring type metaborate groups [107]. A band from ~1617 to ~1622 cm-1

was ascribed to the

bending modes of OH groups [107] and vibrations of bridging oxygen atoms between BO3 and

BO4 groups [87].

Fig. 6.4. FT-IR spectra of BIPLAB:1-5 glasses.

4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 450.0

0.0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

99.9

CM-1

%T

PRH5

PRH1PRH2

PRH

PRH3

PRH4

3430

2923

2853

1456

1377

1046

687

3900

3742

3436

2952

2923

2853

2719

1622

1456

1377 1062

1045

973

952

768

749

697

493

3433

2952

2923

2853

1617

1457

1377

1051

688

491

3436

2952

2923

2853

2322

1623

1457

1377

1214

1089

1062

1050

952

816

761

720

3433

2952

2923

2853

1624

1507

1457

1377

1044

689

25

A band from ~2322 cm-1

was attributed to the O-H bond stretching vibrations [25]. A band from

~2853 cm-1

was ascribed to the Hydrogen bonding [5]. A band from ~2952 cm-1

corresponds to

the Hydrogen bonding [5]. A band from ~3430 to ~3436 cm-1

Table 6.11: FT-IR absorption spectral features and their assignments for BIPLAB:1-5

glasses.

Wave number (cm-1

) FT-IR spectral assignments

~ 493 Bi-O bend in Bi O3 units and stretching vibration in Pb O4 .

~689 to ~720 B-O-B angle bending vibrations from pentaborate groups.

~761 to ~768 Al-O vibrations .

~816 Boroxal ring .

~952 B-O stretching of BO4 units from diborate groups and Pb-O

symmetrical stretching vibrations.

~973 B-O stretching of BO4 units from diborate groups and Pb-O

symmetrical stretching vibrations .

~1044 to ~1048 BO4 vibrations and stretching vibrations of B-O-Bi linkages .

~ 1214 B-O- symmetric stretch in BO3 units from pyro-and ortho –

borate groups.

~1377 B-O vibrations of various borate rings.

~1457 B-O stretching vibrations of BO3 units in chain and ring type

metaborate groups.

~1507 B-O and B-O- stretching vibrations of BO

3 and BO2O

- units.

~1617 to ~1624 Bending modes of OH groups and vibrations of bridging

oxygen atoms between BO3 and BO4 groups.

~2322 O-H bond stretching vibrations.

~2719 Hydrogen bonding.

26

~2853 Hydrogen bonding.

~2952 Hydrogen bonding.

~3430 to ~3436 Characteristic stretching of OH- groups.

~3742 Characteristic stretching of OH- groups.

~3900 Characteristic stretching of OH- groups.

was ascribed to the characteristic stretching of OH- groups [5]. A band from ~3742 cm

-1 was

attributed to the characteristic stretching of OH- groups [5]. A band from ~3900 cm

-1 was

ascribed to the characteristic stretching of OH- groups [5]. In borate glasses an isomerization

process between 3 and 4 coordinated borons is always present: B Ø2O- ↔BØ4

− ,where Ø stands

for an oxygen atom bridging two boron atoms [121]. The increase of PbO content to the glass

matrix promotes the conversion of some BO3 units to BO4.

6.5 CONCLUSIONS

The refractive index range from 1.616 to 1.856 indicating the increase of RI with increase of

PbO and decrease of B2O3. The numerical aperture (NA) value range from 0.23 to 0.26

indicating the suitability of the material as core material for optical fibers. The higher magnitude

refractive indices of all the five glasses make them to fit as the lasing candidates and core

materials of the optical fiber.

The rms deviation of the observed and calculated energies range from 14.62 to 18.838,

in good agreement with the literature. The sum of Slater parameter, 𝚺FK, indicates the net

electrostatic interaction experienced by Pr3+

ions in the host matrix. The positive value of

bonding parameter δ indicates that the bonds between Pr3+

ion and ligands are covalent in nature.

27

The quality of the least square fit given by rms deviation between the experimental and

calculated oscillator strengths is better when the hypersensitive transition 3H4

3P2 is omitted,

ranges from ± 0.843 to ± 1.223.

It is observed that Ω6 > Ω4 > Ω2 for BIPLAB: 1, 2 and 4 glasses and Ω4 > Ω6 > Ω2 for

BIPLAB:3 and 5 glasses. The parameter Ω2 is associated with asymmetry of the ligand field near

the rare earth ion. Ω2 value are in the order BIPLAB:1 > BIPLAB:5 > BIPLAB:3 > BIPLAB:2

> BIPLAB:4. The higher values of Ω2 obtained for BIPLAB: 1, 3 and 5 glasses in the present

study indicate that the asymmetry and covalence of the ligand field at the rare earth site are

higher as expected from bonding parameter. The spectroscopic quality factor Ω4 / Ω6 observed

range from 0.954 to 1.047 indicating that these glasses are fairly rigid as compared to other

glasses reported in literature [146]. Thus the obtained J-O parameters indicate that the present

glasses are more potential lasing candidates.

The emission bands corresponding to 3P0

3H4 and

1D2

3H4 transitions are more

intense compared to 3P1

3H5 and

3P0

3F2 transitions. The emission band of the transition

3P1

3H5 has been almost merged with that of

3P0

3H4 transition. Computed radiative life times for

the transitions are in the order 3F4>

1G4 >

1D2 >

1I6 >

3P1 >

3P0 >

3P2. Higher life times

comparative to others’ indicate better lasing transitions. It is observed that the branching ratios of

the transitions 3P1

3F3 ,

3P0

3F2 ,

iD2

3F4,

1G4

3H5 ,

3H6 exhibit higher values. An

important lasing transition for optical fiber is 1G4

3H5. In the present glasses this transition

exhibits high values of branching ratios. This property is observed for ZBLN, (Ge S2 )80 (Ge

2 S3)

20 and Ga-La-S fluoride and sulfide glasses for optical fibers. emission peak wavelengths( λp)

show the red shift that may be attributed to the site distribution of Pr3+

ions in the vicinity of

ligand fields. The values of ζe for 3P0

3H4 transition are in the order BIPLAB:3 >

28

BIPLAB:5> BIPLAB:1> BIPLAB:4> BIPLAB:2 and for 1D2

3H4 transition are in the order

BIPLAB:4> BIPLAB:5> BIPLAB:3> BIPLAB:1> BIPLAB:2. The high values of emission

cross-sections indicate that these glass matrices are good laser active media indicating the

increase in the gain parameter. Application of J-O theory to Pr3+

ion in analyzing the radiative

parameters yield poor agreement between calculated and experimental values due to the strong f-

d mixing which is not accounted by the theory.

Both indirect and direct mobility gap values show a non-uniform variation with increase of

PbO content and decrease of B2O3 content indicating the variation of switching action, which

might be due to the change in the number of non-bridging oxygen atoms. The variation in the

values of optical band gap energy can thus be attributed to the similar variation in the phonon-

assistant indirect transitions.

From FT-IR spectra functional groups were identified. The increase of PbO content to the

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