V. Ravi Kumar

Optical absorption and photoluminescence properties of Eu3+-doped ZnF2-PbO-TeO2 glasses

Several physical, optical absorption and photoluminescence properties of Eu3+-doped ZnF2–PbO–TeO2 glasses have been studied. From the measured intensities of various absorption bands of these glasses the Judd–Ofelt parameters Ω2, Ω4 and Ω6 have been computed. The Judd–Ofelt theory has been applied to characterize the photoluminescence spectra of these glasses. From this theory, various radiative properties, such as transition probability, A, branching ratio, βr, and emission cross-section, σEP, for various emission levels of these glasses, have been determined and reported.

Dielectric properties of ZnF2-PbO-TeO2 glasses

Abstract The dielectric constant ϵ, loss tan δ and a.c. conductivity σ of four compositions of ZnF2-PbO-TeO2 glasses with successive decrease in PbO and TeO2 concentration were measured in the frequency range 5 × 102−105 Hz and in the temperature range 30 to 200 °C. The dielectric breakdown strength of these glasses were also determined at room temperature in the air medium. The variation of dielectric loss with temperature for these has glasses has exhibited dielectric relaxation effects. The rate of increase of ϵ and tan δ with temperature beyond the relaxation region has been found to increase with an increase in the PbO concentration whereas the dielectric breakdown strength, the activation energy for dipoles and for a.c. conduction in the high-temperature region, has been found to decrease with an increase in the concentration of PbO. These results have been understood due to the increase in the degree of depolymerization of the glass network with increase in the modifier concentration PbO. An attempt has also be made to expain conduction in these glasses on the basis of quantum mechanical tunneling (QMT) model.

Spectroscopic and dielectric studies on PbO–MoO3–B2O3 glasses incorporating small concentrations of TiO2

This paper deals with the investigation of a variety of physical properties including dielectric constant (over a wide range of frequency and temperature), optical absorption, luminescence, electron spin resonance (ESR) and infrared spectra of a TiO2-doped lead molybdenum borate glass system. The composition chosen for the study is 30PbO–4MoO3–(66–x)B2O3:xTiO2 (with x ranging from 0.2 to 2.0). Quantitative analysis of the results of this study shows that, when the content of TiO2 is around 0.8 mol%, the titanium ions exist predominantly in the tetravalent state and occupy substitutional positions in the glass network. A substantial increase in the insulating strength of these glasses on TiO2 doping has also been observed. When the concentration of TiO2 is increased beyond 0.8 mol%, it is observed that titanium ions exist primarily in the Ti3+ state and molybdenum ions in the Mo5+ state; analysis of the results further suggests that both of these ions participate in the depolymerization of the glass network.

Role of modifier oxide in emission spectra and kinetics of Er–Ho codoped Na2SO4–MO–P2O5 glasses

The glasses of the composition 19Na(2)SO(4)-20MO-60P(2)O(5): 1.0Ho(2)O(3)/1.0Er(2)O(3) (M=Mg, Ca, and Ba) have been synthesized. Optical absorption and fluorescence spectra (in the spectral range 350-2100 nm were studied at ambient temperature. The spectra were characterized using Judd-Ofelt theory. From the luminescence spectra, various radiative properties like transition probability A, branching ratio β and the radiative life time τ for blue (B), green (G) and red (R) emission levels of these glasses have been evaluated. The energy transfer between the two rare earth ions (Ho(3+) and Er(3+)) in co-doped Na(2)SO(4)-MO-P(2)O(5) glass systems in the visible and NIR regions has also been investigated. Highest intensity, the highest quantum efficiency and maximum energy transfer with low phonon losses of B, G, and R lines has been observed in BaO mixed glasses. The reasons for such higher values of these parameters have been discussed in the light of varying field strengths at the rare earths ion site due to replacement of one modifier oxide with the other. The enhanced intensity of NIR emission (at 2.0 μm) has also been discussed in terms of cross relaxation of Er(3+) ions from (4)I(13/2) level to (5)I(7) of Ho(3+) ions.

Optical absorption and photoluminescence properties of Pr3+-doped ZnF2PbOTeO2 glasses

Abstract Several physical properties, optical absorption and photoluminescence properties of Pr3+-doped ZnF2PbOTeO2 glasses are studied. From the measured intensities of various absorption bands of these glasses the Judd-Ofelt parameters Ω 2 , Ω 4 and Ω 6 have been computed. The Judd-Ofelt theory has been applied to characterise the photoluminescence spectra of these glasses. From this theory, various radiative properties like transition probability A, branching ratio βr and emission cross section σPE for various emission levels of these glasses have been determined and reported.

Optical properties of Nd3+ ions in cadmium borosulphate glasses and comparative energy level analyses of Nd3+ ions in various glasses

Abstract Optical properties of Nd 3+ ions are studied in the following cadmium borosulphate(CBS) glasses: CdSO 4 + B 2 O 3 and R 2 SO 4 + CdSO 4 + B 2 O 3 (R 2 SO 4  Li 2 SO 4 · H 2 O, Na 2 SO 4 , K 2 SO 4 and Gd 2 (SO 4 ) 3 ·8H 2 O). The assigned energy level data of Nd 3+ (4f 3 ) in CBS glasses as well as the data that are available for other 20 Nd:glass systems in the literature are analysed in terms of a parametrized free-ion Hamiltonian model ( H FI ) that consists of 20 interaction parameters of atomic nature. The systematic theoretical energy level analysis with uniform H FI results in good correlation between calculated and observed energies. Judd-ofelt intensity parameters for f-f transitions are derived from the integrated absorption spectra and are used to calculate the radiative properties for fluorescent levels of Nd 3+ ions in borosulphates glasses. The variations in the spectroscopic properties due to compositional changes of the glasses are discussed.

Elastic properties of ZnF2-PbO-TeO2 glasses doped with certain rare earth ions

The elastic moduli (Y, η, σ andH) and some thermodynamical parameters, such as Debye temperatureθD, diffusion constantDi and latent heat of melting ΔHm, of ZnF2-PbO-TeO2 glasses doped with some rare earth (Pr3+, Nd3+, Eu3+ and Tb3+) ions are determined as functions of temperature using piezo electric composite oscillator technique. All the parameters are found to decrease with increase in the atomic number Z of the rare earth ions and with increase in the temperature of measurement. The results are explained on the basis of the density of localized bonding defect states within the band gap of the material.

Bioactivity studies on TiO2 -bearing Na2O-CaO-SiO2-B2O3 glasses

Soda lime silica borate glasses mixed with different concentrations of TiO2 are synthesized by the melt-quenching technique. As a part of study on bioactivity of these glasses, the samples were immersed in simulated body fluid (SBF) solution for prolonged times (~21 days) during which weight loss along with pH measurements is carried out at specific intervals of time. The XRD and SEM analyses of post-immersed samples confirm the formation of crystalline hydroxyapatite layer (HA) on the surface of the samples. To assess the role of TiO2 on the formation of HA layer and degradability of the samples the spectroscopic studies viz. optical absorption and IR spectral studies on post- and pre-immersed samples have been carried out. The analysis of the results of degradability together with spectroscopic studies as a function of TiO2 concentration indicated that about 6.0 mol% of TiO2 is the optimal concentration for achieving better bioactivity of these glasses. The presence of the maximal concentration octahedral titanium ions in this glass that facilitates the formation of HA layer is found to be the reason for such a higher bioactivity.

Spectral and fluorescent kinetics features of Nd3+ ion in Nb2O5, Ta2O5 and La2O3 mixed lithium zirconium silicate glasses.

Li(2)O-ZrO(2)-SiO(2):Nd(3+) glasses mixed with Nb(2)O(5), Ta(2)O(5) and La(2)O(3) were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The Judd-Ofelt theory was successfully applied to characterize Nd(3+) spectra of all the three glasses. From this theory, various radiative properties like transition probability A, branching ratio β(r), the radiative lifetime τ(r), for (4)F(3/2) emission level in the spectra of these glasses has been evaluated. The radiative life time for (4)F(3/2) level of Nd(3+) ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied, the La(2)O(3) mixed glass has exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Nd(3+) ions.

Spectroscopic investigations of Pr(III) ions in alkali cadmium borosulphate glasses

Abstract The optical absorption of Pr3+ ions in CdSO4+B2O3 and R2SO4+B2O3+CdSO4 system of glasses (R = Li, Na, K or Gd) have been measured. The assigned energy level data of Pr3+(4f2) are analyzed in terms of a parameterized model Hamiltonian that includes central field, EAVG, two-body electrostatic repulsion, F2,4,6, two-body configuration, α, β, γ, spin-orbit, ξ, spin-other-orbit, M0,2,4, and electrostatically correlated spin-orbit, P2,4,6, interactions. The theoretical analysis of energy levels results in good correlation between calculated and observed energies. Re-analysis of energy levels in some glass systems yields calculated energies which agree with experimental energy levels. The effects of the glass medium on the empirical parameters are examined. The electron paramagnetic resonance (EPR) spectrum of Gd3+: Pr2SO4+CdSO4+ B2O3 glass system has also been studied and the results are discussed. The distinct trends in the Pr glass ion have also been examined from the trend in covalent interaction strengths determined experimentally from the magnitude of the bonding parameter, δ.