3 Chapter 3

Chapter 3

Lasing characteristics of

PbO-Sb2O3-B2O3:Nd2O3 glasses

87

3.1 Introduction:

The laser materials doped with Nd3+ ions [1] have become the hotspot because

Nd3+ ion has large absorption coefficient, wide absorption band, long fluorescence

lifetime, very large fluorescence branching ratio, energy compaction and the possibility

of lasing at different wavelengths at room temperature. They are the most investigated

lanthanide ions, not only due to its NIR emission, but also because of its sensitivity to a

changing crystal field can be used to extrapolate the spectral properties of other Ln ions

in a similar matrices [2]. On the other hand, the study of ion-ion interaction in highly

concentrated Nd3+ doped materials is a matter of both practical and theoretical

importance. High Ln concentration allows reducing the size of the gain media and/or

the pump power required. However, due to inherent disorder of glasses, ions in a nearby

sites may have different physical environment with greatly varying properties and, as a

consequence, special migration of energy and spectral diffusion within the in-

homogeneously broadened spectral profile [3] can occur. It is worthy noticing that the

migration of the electron excitation over the inhomogeneous profile (spectral migration)

and the wavelength dependence of the laser emission under narrow spectral site-

selective pumping.

Nd3+ ion is 4f3 ion with 4I9/2 ground state. The absorption and emission of this

ion has been reported in a number of glasses and crystalline materials because of its

potential applications in laser technology [4-5]. The transition 4I9/2→2P1/2 of Nd3+ ion in

absorption spectra is characteristic of coordination of this ion. Generally it is a strong

band and is desirable in the construction of compact and efficient laser source pumped

by diode laser. The effective coordination of this ion is found to be varying between 6

and 9 with the variation in the transition energy 23,300 cm-1 to 23,400 cm-1 [6]. The J-O

theory works very well for this ion and radiative parameters can therefore be

conveniently evaluated from J-O parameters.

88

3.2 Brief review of previous work done on neodymium doped glasses

Kam and Buddudu [1] have studied luminescence enhancement on Nd3+ and

Ce3+ doped SiO2; Al2O3 sol gel glasses. Wilhelm et al. [7] have reported the

fluorescence life time enhancement of Nd3+ sol-gel glasses by Al codoped ping and

Co2 laser processing. Karthikeyan and Mohan [8] have reported the structural, optical

and glass transition studies on Nd3+ doped lead borate glasses. Sen et al. [9] have

studied spectroscopic properties of Nd3+ doped transparent oxyfluoride glass ceramics.

Annapurna et al. [10] have investigated the NIR emission and up conversion

luminescence spectra of Nd3+: Zno-SiO2-B2O3 glasses. Shen et al. [11] have reported

the compositional effects and spectroscopy of rare earth (Er3+, Tm3+ and Nd3+) in

tellurite glasses. Kumar et al. [12] have explored the stimulated emission and radiative

properties of Nd3+ ions in barium fluorophosphates glass containing sulfate. Chen et al.

[13] have studied ion-implanted waveguides in Nd3+ silicate glasses and Er3+/Tb3+ co

doped phosphate glass. Saisudha and Ramakrishna [14] have found large radiative

transitions probabilities in bismuth borate glasses doped with Nd3+ ions. Rosa-Cruz et

al. [15] have reported the results of their study on spectroscopic characterization of

Nd3+ ions on barium phosphate glasses. Fernandez et al. [16-17] have evaluated the

upconversion losses in Nd3+ doped fluoro arsenate glasses. Surana et al. [18] have

investigated the laser action in neodymium doped zinc chloride boro phosphate

glasses. Vijaya Praksh reported [19] his results of absorption studies of Pr, Nd, Sm,

Dy, Ho and Er ions in NASICON type phosphate glasses Na4 AlZnP3O12. Rao et al.

[20] have reported luminescence properties of Nd3+: emission in violet from yellow in

Nd3+ : SiO2-TiO2-Al2O3 sol-gel glasses. Bouderbala et al. [21] have reported the results

of their studies in infrared and visible room temperature florescence induced by

continuous laser excitation of new Nd3+: phosphate glasses. Cassanjes et al. [22] have

investigated Raman scattering, differential scanning calorimetry and Nd3+ spectroscopy

in alkali niobium tellurite glasses. Mehta et al. [23-24] have investigated the

spectroscopic properties including ESR of Nd3+ doped phosphate and borate glasses.

Kumar and Bhatnagar [25] have reported the effect of the modifier ions on the

covalence of Nd3+ ions in cadmium borate glasses. Srinivas rao et al. [26] have

89

reported the physical and absorption properties of Nd3+ doped mixed alkali fluoro-

borophosphate optical glasses. Ajit kumat et al. [27] have reported the spectroscopic

parameters of Nd3+ ions in phosphate glasses. Joshi and Lohani [28] have investigated

the non radiative energy transfer from Tm3+ to Ho3+ and Nd3+ in zinc phosphate glass.

Dewar et al. [29] have studied the optical and acousto-optical properties of Nd:

phosphate glasses. Ning et al. [30] have fabricated Ti: sapphire laser pumped Nd:

tellurite glass laser. Pozza et al. [31] have investigated the absorption and

luminescence spectroscopy of Nd3+ and Er3+ in zinc borate glass. Ratnakaran and

Buddudu [32] have reported the optical absorption spectra and laser analysis of Nd3+

ions in fluoroborate glasses. Sen and Stebbains [33] have studied structural role of

Nd3+ in SiO2 glass using NMR studies. Ebendorff et al. [34] have studied the

spectroscopic properties of Nd3+ ions in Phosphate glasses.

3.3 Sample preparation

The molar composition of the glasses under study is 30 PbO-25 Sb2O3-(45-x)

B2O3 –x Nd2O3 where x= 0, 0.2, 0.4, 0.6 and 1 .The samples were labeled as N0, N2,

N4, N6, N8 and N10 respectively. Appropriate amounts of AR grade reagents of PbO,

Sb2O3, B2O3, and Nd2O3 powders are thoroughly mixed in agate mortar and melted in a

silica crucible in the temperature range of 900 to 950 °C in a programmable electrical

furnace for thirty minutes until bubble free liquid is formed. The resultant melt is

poured in a brass mold and subsequently annealed at 250 °C for 2 h. The samples

prepared were then ground and optical polished to the dimensions of 1 cm × 1 cm × 0.2

cm. The detailed composition of the samples is

N0: 30 PbO-25 Sb2O3-45 B2O3-0 Nd2O3

N2: 30 PbO-25 Sb2O3-44.8 B2O3-0.2 Nd2O3

N4: 30 PbO-25 Sb2O3-44.6 B2O3-0.4 Nd2O3

N6: 30 PbO-25 Sb2O3-44.4 B2O3-0.6 Nd2O3

N8: 30 PbO-25 Sb2O3-44.2 B2O3-0.4 Nd2O3

N10: 30 PbO-25 Sb2O3-44 B2O3-1.0 Nd2O3

90

3.4 Physical parameters

Various physical properties like density, molar volume, oxygen mol%, oxygen

packing density, Nd3+ ion concentration, inter ionic distance, refractive index, polaran

radius, molar refraction and polarizability of Nd3+ doped glasses are calculated and

presented in Table 3.1.

As the concentration of Nd3+ ions increased, a considerable increase in the

density or a considerable decrease in the molar volume of samples is observed.

Modification of the geometrical configurations of the glass network, change in

coordination and the variation of dimensions of the interstitial holes can be considered

as responsible for such a variation of density. Oxygen packing density is also found to

increase with the increase in the concentration of Nd3+ ions. Such an increase indicates

an increase in the structural compactness of the samples.

3.5 Characterization

3.5.1 XRD

The X-ray difractograms are important to know the amorphous nature of the

sample. The X-ray diffraction of all the samples were recorded on Rigaku

diffractometer mini flex with CuKɑ radiation. The absence of sharp peaks in the X-ray

diffraction (Fig. 3.1 ) pattern indicates the amorphous (glass) nature of the samples.

3.5.2 Differential scanning calorimetry

The glass transition temperatures of these glasses were determined by differential

scanning calorimtry traces that were recorded using DSC Q20 (TA-Instruments) with a

programmed heating rate of 20 oC per minute in the temperature range 50-500oC and

presented in the figure Fig. 3.2. All DSC traces indicate typical glass transitions with

the inflection points between 380 oC to 390 oC. Although the inflection points of all the

samples appear to be nearly same, it is interesting that the glass transition temperature

shows increasing trend with increase in dopant concentration. The glass transition

temperature for all the samples were presented in the Table 3.2.

Table 3.1 Physical parameters of PbO-Sb2O3-B2O3 glasses doped with Nd3+ ions.

Glass

Physical Parameter N0 N2 N4 N6 N8 N10

1 Average MW(g/mol) 171.16 171.7 172.23 172.76 173.3 173.83

2 Density, ρ (g/cc) (±0.001) 4.972 5.101 5.212 5.316 5.481 5.567

3 Refractive index, n (±0.001) 1.503 1.512 1.517 1.521 1.524 1.529

4 Molar Volume, Vm (MW/ρ) (±0.01) 31.99 33.93 33.41 32.62 32.06 31.31

5 Molar Refraction, RM (±0.001) 9.457 10.181 10.108 9.933 9.809 9.656

6 Polarizability, αe

(×10-24cm3) (±0.001) 3.75 4.034 4.005 3.936 3.886 3.826

7 Oxygen mol % , O (±0.01) 2.4 2.4 2.4 2.4 2.4 2.4

8 Oxygen packing density (gm atom/L) (±0.01) 75.02 70.73 71.83 73.57 74.86 76.65

9 Nd3+ ion concentration, Ni (×1021/cc)(±0.01) 0 0.11 0.22 0.33 0.45 0.58

10 Inter ionic distance, ri (Å) (±0.001) - 20.87 16.57 14.47 13.05 11.99

11 Polaran radius, rp (Å ) (±0.001) - 0.146 0.158 0.165 0.171 0.176

Fig. 3.1 X- ray difractograms of PbO-Sb2O3-B2O3 glasses doped with Nd3+ ions.

Fig. 3.2. Variation of glass transition temperature of PbO-Sb2O3-B2O3 glasses with

increasing in Nd3+ ion concentration.

-0.8

-0.6

-0.4

-0.2

060 110 160 210 260 310 360 410 460

Hea

t flo

w (

W/g

m)

Temperature

N2

N4

N6

N8

N10

93

Table 3.2 Thermal parameters of PbO-Sb2O3-B2O3 glasses doped with Nd3+ ions.

Name of the sample Glass Transition Temperature (C) (±1)

N2 384

N4 385

N6 387

N8 391

N10 392

3.5.3 FTIR spectra

Fourier transform infrared spectra of Nd3+ doped PbO-Sb2O3-B2O3 glasses is

shown in the Fig. 3.3. The infrared transmission spectra of PbO-Sb2O3-B2O3 :Nd2O3

glasses exhibited bands originated from borate groups at 1200 cm-1 to 1400cm-1 due

to asymmetric stretching of trigonal BO3 units, 1050 cm-1 due to stretching of

tetrahedral BO4 units and another band at 688 cm-1 due to bending of B-O-B

linkages in the borate network [35]. The 1 vibrational band of SbO3 units appeared

at 930 cm-1. The 3 vibrational bands of SbO3 units merged with the band due to

bending vibrations of B-O-B linkages and may have formed a common vibrational

band due to B-O-Sb linkages [36]. In addition, a band due to PbO4 structural groups

at about 462 cm-1 [37] is also observed for all the samples. The bands at 1750 cm-1

and 3000 cm-1 may be due to the stretching vibration of hydroxyl (OH) complexes,

which are due to the absorbed water molecules on the surface of the material.

Fig. 3.3 FTIR spectra of PbO-Sb2O3-B2O3 glasses doped with Nd3+ ion.

400 800 1200 1600 2000 2400 2800 3200

Tra

ansm

itta

nce(

%)

Wavenumber (cm-1)

BO3 Units

B-O-B linkage

PbO4 Units ν1-Sb2O3 Units

BO4 Units

N0

N2

N4

N6

N8

N10

OH Units

OH Units

95

3.6 Optical absorption

The optical absorption spectra (Fig. 3.4) of Nd3+ doped PbO-Sb2O3-B2O3 glasses was

recorded at room temperature in the spectral wavelength range covering 300–2000 nm

with a spectral resolution of 1 nm, have exhibited twelve well resolved bands with

respect to its ground state 4I9/2 at

4D5/2 (368nm)

2D5/2 +2P1/2 (433nm)

4G11/2 (463nm)

2K15/2+2D3/2+

2G9/2 (478nm)

4G9/2 (516 nm)

4G7/2 (527 nm)

4G5/2 + 2G7/2 (583 nm)

2H11/2 (632 nm)

4F9/2 (681 nm)

4F7/2 + 4S3/2 (747 nm)

4F5/2 + 2H9/2 (804 nm)

4F3/2 (877 nm)

The increase in the concentration of neodymium ions in the glass matrix does

not alter the spectral positions of the absorption bands significantly but the absorption

strengths under given peek is found to be increased.

3.6.1 Optical parameters

The optical band gap energy is calculated from the extrapolation of linear region

of graph (α ħω)1/2 against ħω and presented in the Fig. 3.5. Optical band gap energies of

the samples were decreasing with increasing the concentration of Nd3+ ions. Urbach

plots are obtained by plotting ln(α) against ħω. The values of Urbach energy (ΔE) are

calculated by determining the reciprocals of the slopes of linear region of curve.

Fig. 3.4 Optical absorption spectra of PbO−Sb2O3−B2O3 glasses doped with Nd3+ recorded at room temperature. All

transitions are from the ground state 4I9/2.

350 450 550 650 750 850

Abs

orba

nce

(a.u

)

Wavelength (nm)

N0

N2

N4

N6

N8

N10

4F3/2

4F5/2+2H9/2

4F7/2+4S3/2

4F9/22H11/2

4G5/2+2G7/2

4G7/24G9/2

2K15/2 +2D3/2+2G9/2

4G11/2

2D5/2+2P1/2

4I9/2

4D5/2

Fig. 3.5 Tauc plots for evaluation of optical band gap energy of PbO-Sb2O3-B2O3 glasses doped with Nd3+ ions.

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10

3.3 3.32 3.34 3.36 3.38 3.4 3.42 3.44 3.46

(αhυ

)1/2cm

-1/2

eV1/

2

hυ (eV)

N0

N2

N4

N6

N8

N10

98

The Urbach energy indicates the degree of disorder i.e. higher is the Urbach

energy, higher is the disorder. It is observed that the Urbach energy of all the samples is

increasing with increase in the concentration of Nd3+ ions. Similarly cut of wavelengths

are calculated for all the samples which are observed to be shifting towards lower

wavelength with increase in the concentration of Nd3+ ions. Table 3.3 shows the optical

parameters of PbO-Sb2O3-B2O3 doped with Nd3+ ions.

Table 3.3 Optical parameters of Nd3+ doped lead antimony borate glasses.

GlassPhysical Parameter N0 N2 N4 N6 N8 N10

1 Cutoff wavelength, λ (nm)(±1)

353 355 356 357 359 361

2 Optical bandgap energy, Eopt

(eV) (±0.001)3.399 3.391 3.386 3.383 3.38 3.374

3 Urbach Energy, ΔE (eV)(±0.001)

0.511 0.523 0.529 0.538 0.551 0.563

3.6.2 Oscillator strengths

The intensities of absorption transitions of optical absorptions are measured in

terms of oscillator strengths (fexp) and determined from the relative areas under the

absorption bands. The experimental oscillator strengths (fexp) and calculated oscillator

strengths are computed by using the equations 1.9 and 1.23 respectively and presented

in Table 3.4. The small value of root mean square (rms) deviations between

experimental and calculated oscillator strengths indicated good agreement between

them.

Table 3.4 The experimental (fexp x10-6) and calculated (fcal x10-6) spectral intensities of Nd3+ doped antimony lead borate

glasses. All the transitions are from its ground state 4I9/2.

Transitions fromground state 4I9/2

N2 N4 N6 N8 N10

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

4F3/2 2.3 2.12 2.34 2.4 2.44 2.4 2.67 2.61 2.73 2.72

4F5/2 + 2H9/2 7.01 6.66 7.28 7.46 7.7 7.46 8.44 8.07 8.82 8.31

4F7/2 + 4S3/2 9.1 9.3 9.6 10.35 10.22 10.35 11.21 11.17 11.14 11.45

4F9/2 0.38 0.69 0.58 0.77 0.63 0.77 0.69 0.83 0.73 0.85

2H11/2 0.13 0.19 0.14 0.21 0.15 0.21 0.17 0.23 0.19 0.24

4G5/2 + 2G7/2 21.29 21.3 22.77 24.14 24.14 24.14 26.33 26.33 26.71 26.71

4G7/2 3.8 3.49 3.88 3.95 4 3.95 4.43 4.3 4.45 4.42

4G9/2 0.67 0.7 0.68 0.78 0.77 0.78 0.86 0.84 1.13 0.86

2k15/2+2D3/2+

2G9/2 0.76 0.76 1.17 1.17 1.27 1.38 1.38 1.38 1.46 1.46

4G11/2 0.84 0.98 0.86 1.1 0.98 1.1 1.09 1.2 1.07 1.24

2P1/2+2D5/2 0.47 0.47 0.72 0.54 0.94 0.54 0.97 0.59 1 0.61

4D5/2 3.92 5.1 4.67 5.79 5.21 5.79 5.41 6.31 5.56 6.56

RMS Deviation 0.4 0.6 0.24 0.32 0.39

100

3.6.3 Judd-Ofelt parameters

Judd-Ofelt theory has been used to investigate radiative nature of trivalent rare

earth ions in a variety of laser host materials [38-39]. The calculated oscillator strengths

fcal were determined by using the Judd-Ofelt theory. Judd–Ofelt intensity parameters Ωλ

for these glasses were evaluated with the usual procedure i.e. by performing least square

fit analysis between the experimental oscillator strengths( fexp) , theoretical oscillator

strengths (fcal), the wave numbers (cm-1) and doubly reduced matrix elements U(λ)2

with λ = 2, 4, 6.

The computed data of U(λ)2 for different absorption states of rare earth ions

[40] and also for different emission levels is available in literature. According to the

literature [41-45], the unit tensor operator will not significantly change their values

depending on host charge around the dopant rare-earth ions in host material. Therefore

the literature data have been used in the parameterization of absorption and

photoluminescence spectra of the Nd3+ glasses studied and presented in the Table 3.5.

The positions and the spectral intensities of certain transitions of rare earth ions

are very sensitive to the environment of the rare earth ions [46]. These transitions

follows selection rules such as [47-48] ΔJ ≤ 2, ΔL ≤ 2 and ΔS = 0, called as hyper

sensitive transitions. From Fig. 3.4, it is noticeable that the transition 4I9/2 →4G5/2 + 2G7/2

at about 583 nm is much brighter than the other transitions and is a hyper sensitive

transition. The hyper sensitive transitions (bands) are normally associated with the

larger values of U22 and hence intimately related to Ω2.The intensity parameter Ω2

indicates the covalency of the rare earth ligand bond and increases with increase in the

intensity of the hyper sensitive transition [49]. The same tendency is observed for the

present glass system.

The Judd-Oflet parameters of all the samples were calculated and presented in

Table 3.6. The intensity parameter Ω2 is associated with the symmetry of ligand field

around rare earth ion and hence the covalency of rare earth ion. For the present study,

Ω2 follows the order N10 > N8 > N6 > N4 > N2. This trend indicates that the symmetry

of the site associated with Nd3+ ion is highest for N2 glasses and lowest for N10 glasses.

Table 3.5 Energy level assignments and matrix elements of U(λ)2 for Nd3+ ions

S.No Transition Wave length λ (nm) wavenumber (cm-1) U22 U42 U62

1 4F3/2 877 11402 0 0.23 0.0571

2 4F5/2 + 2H9/2 804 12437 0.0005 0.2314 0.4001

3 4F7/2 + 4S3/2 747 13386 0.0009 0.0448 0.6583

4 4F9/2 681 14684 0.0009 0.0094 0.0402

5 2H11/2 632 15822 0.0006 0.0026 0.01

6 4G5/2 + 2G7/2 583 17152 0.9753 0.5995 0.0859

7 4G7/2 527 18975 0.0536 0.1557 0.0515

8 4G9/2 516 19379 0.0066 0.0002 0.0298

9 2k15/2+2D3/2+

2G9/2 478 20920 0.0000 0.0052 0.0143

10 4G11/2 463 21598 0.001 0.0404 0.0216

11 2P1/2+2D5/2 433 23094 0.0000 0.0366 0.0000

12 4D5/2 368 27173 0.0001 0.2542 0.0457

102

Table 3.6 Judd - Ofelt Ωλ×1020 (cm2) parameters of Nd3+ doped lead antimony borate

glasses along with trends of a number of other glass systems containing Nd3+ ions.

Glass Ω2 Ω4 Ω6 Trend Reference

N2 5.72 3.77 6.89 Ω6>Ω2>Ω4 Present work

N4 6.12 4.032 7.22 Ω6>Ω2>Ω4 Present work

N6 6.46 4.31 7.66 Ω6>Ω2>Ω4 Present work

N8 7.01 4.68 8.22 Ω6>Ω2>Ω4 Present work

N10 7.02 4.89 8.41 Ω6>Ω2>Ω4 Present work

PKMAN10 6.22 5.95 6.83 Ω6>Ω2>Ω4 [50]

K2O-PbO-B2O3 5.90 5.71 6.21 Ω6>Ω2>Ω4 [51]

30Li2O-70B2O3 4.20 3.89 4.74 Ω6>Ω2>Ω4 [52]

3Nd2O3-97[30PbO-70B2O3] 3.96 3.77 4.88 Ω6>Ω2>Ω4 [14]

3Nd2O3-97[40PbO-60B2O3] 3.59 3.50 5.62 Ω6>Ω2>Ω4 [14]

3Nd2O3-97[50PbO-50B2O3] 3.59 3.02 5.32 Ω6>Ω2>Ω4 [14]

3Nd2O3-97[60PbO-40B2O3] 3.61 3.02 5.34 Ω6>Ω2>Ω4 [14]

3Nd2O3-97[70PbO-30B2O3] 3.52 2.98 5.48 Ω6>Ω2>Ω4 [14]

LiCdBs 34.51 10.17 36.89 Ω6>Ω2>Ω4 [53]

NaCdBs 21.06 20.85 27.99 Ω6>Ω2>Ω4 [53]

Vitreous borate 4.30 3.60 4.70 Ω6>Ω2>Ω4 [54]

10Na2O-90B2O3 3.40 2.90 4.30 Ω6>Ω2>Ω4 [55]

PKBAFN(2) 6.60 6.36 7.30 Ω6>Ω2>Ω4 [56]

30CaO-70B2O3 4.4 3.7 4.6 Ω6>Ω2>Ω4 [57]

SBBI 4.72 2.12 3.93 Ω2 >Ω6>Ω4 [58]

SBBI 4.81 1.97 3.94 Ω2 >Ω6>Ω4 [58]

103

3.6.4 Radiative properties

Various radiative parameters such as electric dipole line strength (Sed), magnetic

dipole line strength (Smd), radiative transition probability (AR), total radiative transition

probabilities(AT), the radiative decay times (τR), and branching ratio(βR) of Nd3+ doped

lead antimony borate glasses were calculated using the equations

1.14,1.15,1.25,1.26,1.27 and 1.29 respectively. The radiative parameters of lead

antimony borate glasses for 1% of Nd3+ are presented the Table 3.7.

The values of the branching ratios βR for the 4F3/2 → 4IJ ( J=15/2, 13/2, 11/2 and

9/2) transition depends upon the Ω4/Ω6 since Ω2 does not contribute in determining the

intensity of these bands as U22 is zero for these transitions. In lead antimony borate

glasses, approximately 35% of transition terminates at the 4I9/2 state, 53% at 4I11/2 state,

11% at 4I13/2 state and 5% radiate to the 4I15/2 states.

104

Table 3.7 Electric dipole line strength (Sed), magnetic dipole line strength (Smd),radiative transition probability (AR) branching ratio(βR) , the total radiative transitionprobabilities(AT) and radiative decay times (τR) of Nd3+ doped lead antimony borateglasses.

InitialІ(S,L)J>

FinalІ(S',L')J>

wave number(cm-1)

Sed x1022

(cm2)Smd x1022

(cm2)A (s-1) βR %

4G9/24G7/2 483 204.31 16.72 0.06 02G7/2 2319 125.59 34.52 4.74 0.034G5/2 2408 258.2 0 8.34 0.052H11/2 3607 200.49 0.06 21.78 0.144F9/2 4890 199.56 3.27 54.99 0.354S3/2 6036 98.32 0 50.03 0.324F7/2 6126 479.5 0.21 255.22 1.63

2H9/2 7030 127.66 0.49 103.08 0.664F5/2 7078 189.68 0 155.64 0.994F3/2 8102 150.81 0 185.6 1.184I15/2 13626 272.15 0 1593.29 10.164I13/2 15690 894.2 0 7992.49 50.944I11/2 17672 320.69 0.04 4096.14 26.114I9/2 19531 67.7 0.01 1167.36 7.44

∑A (s-1)= 15688 τR (μs)= 63

4G7/22G7/2 1836 27.31 0.67 0.5 04G5/2 1925 144.39 27.19 3.61 0.032H11/2 3124 117.45 0 10.36 0.084F9/2 4407 14.79 0.02 3.67 0.034S3/2 5553 93.67 0 46.39 0.364F7/2 5643 147.81 1.1 77.47 0.6

2H9/2 6547 399.39 0 324.2 2.534F5/2 6595 256.17 0.7 213.19 1.664F3/2 7619 98.23 0 125.67 0.984I15/2 13143 15.78 0 103.64 0.814I13/2 15207 156.39 0 1590.89 12.414I11/2 17189 487.87 0 7167.14 55.934I9/2 19048 157.45 0 3147.53 24.56

∑A (s-1)= 12814 τR (μs)= 78

105

InitialІ(S,L)J>

FinalІ(S',L')J>

wave number(cm-1)

Sed x1022

(cm2)Smd x1022

(cm2)A (s-1) βR

4G5/24F9/2 2482 116.96 0 6.9 0.034S3/2 3628 88.1 0 16.23 0.084F7/2 3718 217.72 0.13 43.19 0.21

2H9/2 4622 10.91 0 4.16 0.024F5/2 4670 250.43 0.02 98.38 0.474F3/2 5694 364.55 0.03 259.58 1.254I15/2 11218 3.7 0 20.16 0.14I13/2 13282 57.02 0 515.28 2.494I11/2 15264 221.81 0 3042.42 14.684I9/2 17123 863.39 0 16717.54 80.67

∑A (s-1)= 48 τR (μs)= 20833

2H11/24F9/2 1283 92.78 4.1 0.4 0.094S3/2 2429 28.1 0 0.78 0.174F7/2 2519 129.37 0 3.99 0.88

2H9/2 3423 250.83 15.23 20.72 4.574F5/2 3471 21.03 0 1.7 0.374F3/2 4495 7.2 0 1.26 0.284I15/2 10019 118.32 0 229.47 50.614I13/2 12083 13.01 0.93 47.79 10.544I11/2 14065 12.49 0.26 68.59 15.134I9/2 15924 10.11 0 78.73 17.36

∑A (s-1)= 453 τR (μs)= 2205

4F9/24S3/2 1146 2.05 0 0.01 04F7/2 1236 140.32 28.68 0.75 0

2H9/2 2140 38.43 19.22 1.36 04F5/2 2188 124.08 0 3.01 04F3/2 3212 100.8 0 7.73 04I15/2 8736 657.82 0 1014.9 0.224I13/2 10800 553.08 0 1612.27 0.354I11/2 12782 331.65 0.16 1603.57 0.354I9/2 14641 43.39 0.11 316.03 0.07

∑A (s-1)= 4559 τR (μs)= 219

106

InitialІ(S,L)J>

FinalІ(S',L')J>

wave number(cm-1)

Sed x1022

(cm2)Smd x1022

(cm2)A (s-1) βR

4F5/24F3/2 1024 81.89 34.02 0.5 0.014I15/2 6548 194.09 0 210.17 4.094I13/2 8612 427.41 0 1052.89 20.494I11/2 10594 112.26 0 514.81 10.024I9/2 12453 451.22 0 3360.75 65.4

∑A (s-1)= 5139 τR (μs)= 194

4F3/24I15/2 5524 22.89 0 22.33 0.574I13/2 7588 177.93 0 449.73 11.434I11/2 9570 411.22 0 2085.1 53.014I9/2 11429 159.39 0 1376.6 34.99

∑A (s-1)= 3934 τR (μs)= 254

3.7 Photoluminescence

The fluorescence spectra of Nd3+ in the wavelength range 800nm to 1500 nm

recorded with an excitation wavelength of 808 nm and was shown in the Fig. 3.6. The

spectra shows a broad band at 898 nm, a strong band at 1058 nm and another band at

1328 nm. These bands are identified as

4F3/2→4I9/2 (898 nm)

4F3/2→4I11/2(1056 nm)

4F3/2→4I13/2(1328 nm)

respectively. The intensity of the bands is observed to be increasing with concentration

of Nd3+ ions, but no considerable shift in the position is observed.

Fig. 3.6 Normalized emission spectra of PbO - Sb2O3 - B2O3 glasses doped with Nd3+ ions recorded at room temperature(λexc=808 nm).

0

0.2

0.4

0.6

0.8

1

800 900 1000 1100 1200 1300 1400

Nor

mal

ized

inte

nsit

y (A

.U.)

Wavelength (nm)

N2

N4

N6

N8

N10

4F3/2 →4I11/2

4F3/2 →4I9/2

4F3/2 →4I13/2

3.7.1 Stimulated emission cross section

An efficient laser transition is characterized by a large stimulated emission

cross section while the induced emission cross sections are characterized by Judd-

Ofelt theory. The stimulated emission cross-section is given by Fuchtbabauer-

Ladenburg method [59]

),(8 2

4

JJAcn T

eff

p

3.1

where λP is the peak wavelength, Δλeff is the effective bandwidth of the emission

band, n is the refractive index of the sample and AT(ψJ,ψʹJʹ) is the total spontaneous

emission probability. The effective band width and emission cross- section values

are presented in the Table 3.8.

Table 3.8 Emission cross sections of Nd3+ doped lead antimony borate glasses for

the transitions 4F3/2 →4 I J ( J=13/2, 11/2,9/2).

Transition λP Δλeff σe (x10-20) cm2

4F3/2→ N2 N4 N6 N8 N10 N2 N4 N6 N8 N10

4I13/2 1329 29 30 31 33 34 2.22 2.26 2.32 2.35 2.34

4I11/2 1059 25 26 27 28 29 4.77 4.84 4.96 5.07 5.13

4I9/2 896 48 49 50 53 54 0.81 0.85 0.89 0.91 0.93

Fig 3.7 shows a partial energy diagram of the excited manifolds of Nd3+ ions

and several relevant transitions corresponding to the excited 4F3/2 state absorption

and emission. The three excited state absorption transitions correspond to the three

laser levels at 1.35 μm, 1.06 μm and 0.88 μm. The energy level separations between

the 4F3/2 and the upper 4G7/2,2G9/2 and 2P1/2 levels are in all cases close enough to the

energies of possible laser transitions from the 4F3/2 level to lower terminal levels4I13/2,

4I11/2 and 4I9/2, respectively. But among the three transitions from 4F3/2 , the

transition 4F3/2 → 4I11/2 will be a potential lasing transition because of its higher

stimulated emission cross- section (5.13×10-20 cm2) and higher branching ratio (53

%). An electric dipole transition between 4F3/2 and 2G9/2 level near 1.06 μm could

109

reduce the net cross-section for stimulated emission between4F3/2 and 4I11/2 level as

absorbed by Vance .

Fig. 3.7 Energy level diagram of Nd3+ doped lead antimony borate glasses.

3.7.2 Decay curves

The Fig 3.8. shows the decay profile of the 4F3/2→4I11/2 transition of Nd3+

doped lead antimony borate glasses excited at 808 nm wavelength recorded at room

temperature. The experimental life times along with the branching ratios and

emission cross-sections of all the glasses are presented in the Table 3.9

When the Nd3+ ion is excited from its ground state to the levels having energy

higher than that of 4F3/2, they decay non-radiatively to lower levels down to the 4F3/2

state due to very small energy gaps between the adjacent energy levels. As the

energy gap between the metastable 4F3/2 level and its lower level 4I13/2 is sufficiently

large (5600 cm−1 approximately), radiative transitions will predominate here over

the non-radiative transitions state depends upon the values of J-O parameters,

especially on Ω4 and Ω6 , as well as on the host refractive index. It represents a mean

110

value over the different sites occupied by the Nd3+ ions in the glass matrix and it is

higher than that determined experimentally from the luminescence decay. This

reduction in experimental lifetime can be explained by considering all the possible

relaxation processes relative to the excited Nd3+ ions. If the experimentally

measured lifetime of the emitting state is denoted by τ, then the total decay rate (1/τ)

is the sum of radiative (Ar ) and non-radiative(Wn−r ) decay rates. Therefore,

rnr WA 1

3.2

In glasses, principally, there are four non-radiative processes contributing to

the reduction of measured lifetime of the emitting level.

W n−r = Wm−p + W c−q + W e−t + WOH 3.3

where Wm−p, Wc−q, We−t and WOH denotes the non-radiative decay rates

corresponding to the multi phonon relaxation process, concentration quenching,

energy transfer to another doping impurity and hydroxyl (OH−) groups, respectively.

Wm−p decreases exponentially as the energy gap between the neighboring energy

levels increases [60-61]. For the Nd3+ ion, the energy gap between the 4F3/2 level and

its lower level 4I15/2 is sufficiently large enough that Wm−p is negligible compared to

the radiative decay rate of the 4F3/2 level of the Nd3+ ion in lead antimony borate

glasses. For weak concentrations, the non-radiative relaxations due to ion–ion

interactions (Wc−q and We−t) will be almost negligible and the radiative lifetime will

be in agreement with that of experimental values.

In the present glass systems the lifetime is decreased with increase in

concentration of acceptors (Nd3+ ions). The decay curves of the glasses are found to

be varying from exponential to non-exponential and this non- exponential nature

increases with increase of Nd3+ ion concentration due to enhanced energy transfer by

cross-relaxation between two Nd3+ ions [62]. This is also clearly evident from the

decreased lifetimes of the 4F3/2 level in Nd3+ lead antimony borate glasses decreased

from 328 µs to 254 µs 0.2 to 1.0 mol%. The non-exponential nature of the decay

curves is well fitted to the Inokuti–Hirayama model for S=6, indicating that the

dominant interaction for energy transfer through cross-relaxation between Nd3+ ions

is of dipole–dipole type.

111

Fig 3.8. The radiative lifetime of the 4F3/2

Fig. 3.8. Luminescence decay profiles for the 4F3/2 →4F11/2 transition of Nd3+ doped

lead antimony borate glasses.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000 2500 3000

Nor

mal

ized

inte

nsit

y (a

rb.u

nits

)

Time (μs)

N2

N4

N6

N8

N10

112

Table 3.9. Experimental life times, branching ratios (β%), and emission cross

sections (σe) of Nd3+ ion in lead antimony borate glasses for 4F3/2→4F11/2.

Sample τexp (μs) β% σe (×10-20) cm2

N2 207 53.5 4.77

N4 201 53.4 4.84

N6 194 53.3 4.96

N8 184 53.2 5.07

N10 182 53.1 5.13

From the table the branching ratios of samples are almost constant but

however the emission cross-sections are increasing with the concentration of Nd3+

glasses. The N10 glass with more than 50% of branching ratio and higher emission

cross-section is suitable for efficient laser emission.

3.8 Conclusions

Lead antimony borate glasses with different concentrations of neodymium

were prepared by the conventional melt quenching method. The amorphous (glass)

nature was confirmed by the characterization technics such as X-ray difractograms

and DSC traces.

The various physical and parameter of the samples were calculated and

analysed. The density of the glasses is increasing with increase in the mol% of rare

earth ions almost linearly because; the high dense rare earth ions are replacing low

dense B2O3. In general the density and molar volume show opposite behaviour and

the same thing is reflected here. The molar volume of the glass samples is

decreasing with increase in the Nd3+ concentration. The oxygen packing density of

the samples increased with increase in the mol% of rare earth ions. Refractive index

of the samples also increased with increase in concentration whereas molar

refraction and polarizability are decreased.

Fourier transform infrared spectra PbO-Sb2O3-B2O3:Er2O3 glasses exhibited

five conventional bands at 1330 cm-1 (BO3 units), 1050 cm-1 (BO4 units), 688 cm-1

113

(bending vibrations of B-O-B linkages) , 930 cm-1 ( 1 vibrational band of SbO3)

and 462 cm-1 (PbO4 structural groups).

The optical absorption spectra of Er3+ doped lead antimony borate glasses

has exhibited twelve absorption bands. All the bands are identified according to

Carnall. Cut of wavelength is shifting to higher wavelength with increase in Nd3+ ion

concentration. The systematic spectroscopic analysis of neodymium doped lead

antimony borate glass systems has been performed using Judd-Ofelt theory. It has

been found that the Judd–Ofelt intensity parameters follows the trend Ω6>Ω2>Ω4.

The Judd- Ofelt parameters were increasing with Nd2O3 concentration and found to

be maximum for 1 mol% of Nd2O3 (N10).

The fluorescence spectra of Nd3+ shows a broad band at 898 nm, a strong

band at 1058 nm and another band at 1328 nm. The luminescence intensity of

various emission bands increased with the concentration of rare earth ions indicates

that there is no luminescence quenching in these glasses within the concentration

range studied. It has been found that the efficiency of all the transitions i.e.4F3/2→4I9/2 , 4F3/2 →4I11/2 and 4F3/2 →4I13/2 increases as the difference between Ω4 and

Ω6 increases with increasing Nd2O3concentration. In addition, it has been observed

that the emission cross-section for the 4F3/2 →4I11/2 transition is more than 4F3/2→4I9/2

and the 4F3/2 → 4I13/2 transitions for all the glasses. The branching ratio βR values for

the transition 4F3/2→4I11/2 (1.06μm) is about 53% with emission cross-section of

5.13×10-20 cm2. Hence, the transition 4F3/2→4I11/2 will be a potential lasing transition.

To maximize lasing transition fluorescence intensity, preferable condition is Ω6>Ω4

which is observed in Nd3+ doped lead antimony borate glasses.

114

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