T. Sasikala

Optical studies of Sm3+ ions doped Zinc Alumino Bismuth Borate glasses

Zinc Alumino Bismuth Borate (ZnAlBiB) glasses doped with different concentrations of samarium (Sm(3+)) ions were prepared by using melt quenching technique and characterized for their lasing potentialities in visible region by using the techniques such as optical absorption, emission and emission decay measurements. Radiative properties for various fluorescent levels of Sm(3+) ions were estimated from absorption spectral information using Judd-Ofelt (JO) analysis. The emission spectra and con-focal photoluminescence images obtained by 410 nm laser excitation demonstrates very distinct and intense orange-red emission for all the doped glasses. The suitable concentration of Sm(3+) ions in these glasses to act as an efficient lasing material has been discussed by measuring the emission cross-section and branching ratios for the emission transitions. The quantum efficiencies were also been estimated from emission decay measurements recorded for the (4)G5/2 level of Sm(3+) ions. From the measured emission cross-sections, branching ratios, strong photoluminescence features and CIE chromaticity coordinates, it was found that 1 mol% of Sm(3+) ions doped ZnAlBiB glasses are most suitable for the development of visible orange-red lasers.

Optical and luminescent properties of Sm3+ doped tellurite glasses

Glasses with chemical composition of (62-x) TeO(2)+25 ZnO+8 K(2)O+5 CaO+x Sm(2)O(3) (TZKCSmx; x=0.1, 0.5, 1.0, 1.5 mol%) were prepared by melt quenching technique. The absorption spectrum was recorded in the UV-visible and NIR regions. The oscillator strengths of absorption bands were obtained by measuring the area under the bands. Judd-Ofelt analysis has been carried out to estimate the host dependent J-O intensity Ω(λ) (λ=2, 4, 6) parameters by least squares fitting approach. Photoluminescence spectra recorded in the visible region revealed intense green, orange and red emission bands in all the glasses, corresponding to the (4)G(5/2)→(6)H(5/2), (4)G(5/2)→(6)H(7/2) and (4)G(5/2)→(6)H(9/2) transitions respectively. From the emission spectra and J-O intensity parameters, various radiative parameters were calculated from the excited (4)G(5/2) to the lower lying (6)H(J) (J=5/2, 7/2, 9/2, 11/2) multiplet. Quenching of luminescence with the increase of Sm(3+) ions concentration has been observed. Decay times of excited (4)G(5/2) state decrease with the increase of the Sm(3+) ions concentration. The energy transfer mechanism that leads to the quenching of (4)G(5/2) state lifetime has been discussed. Inokuti-Hirayama (I-H) model was used to evaluate various energy transfer parameters, which are the qualitative indicators for the interaction among Sm(3+) ions.

Investigation on 1.07 μm laser emission in Nd3+-doped sodium fluoroborate glasses

Abstract Spectroscopic and fluorescence properties of Nd3+ ions in sodium fluoroborate (SFB) glasses were prepared and characterized through optical absorption, emission and decay measurements. The energy level analysis was carried out using free-ion Hamiltonian model. Experimental oscillator strengths were determined by measuring the area encompassed by the absorption peaks recorded for 1.0 mol.% Nd3+- doped glasses. The Judd-Ofelt parameters (Ω2,4,6) were used to evaluate the laser characteristic parameters such as radiative transition probability (AR), radiative decay time (τR), fluorescence branching ratio (βR) and stimulated emission cross-section (σe) for the 4F3/2 metastable state. The fluorescence spectra for different concentrations of Nd3+ ions were recorded by exciting the samples at 514.5 nm Ar+ ion laser.

Concentration dependent luminescence characteristics of 5D4 and 5D3 excited states of Tb3+ ions in CFB glasses

Calcium fluoroborate (CFB) glasses doped with different concentrations of Tb3+ ions have been prepared with molar composition of (42-x) B2O3 + 20 CaF2 +15 CaO + 15 BaO + 8 Al2O3 + x TbF3 (x=0.05, 0.1, 0.5, 1.0, 2.0 and 4.0) by melt quenching method. Optical absorption spectrum for 1.0 mol% of Tb3+:CFB glass was recorded in UV-Vis-NIR regions. Radiative parameters such as radiative transition probabilities (AR), radiative lifetimes (τR), radiative branching ratios (βR) for the 5D3 and 5D4 excited states have been calculated by using the Judd-Ofelt parameters (Ωλ=2,4,6). The luminescence spectra recorded for different concentrations of Tb3+ ions in CFB glasses exhibit seven and four bands originating from 5D4 and 5D3 excited states respectively. As the concentration of Tb3+ ions increases the intensities of luminescence peaks originating from 5D4 state increases, whereas, the quenching of intensities has been observed for the emission peaks originating from 5D3 state due to energy transfer through cross-relaxation channel (5D3 : 7F6) → (5D4 : 7F0). The experimental lifetimes of 5D4 state for all the concentrations of Tb3+ ions are equal and exhibit single exponential decay with highest quantum efficiency which confirms that these glasses can be used for high intensity green emission even at high concentrations of Tb3+ ions.

Fluorescence Properties of Pr3+ Doped Calcium Fluoroborate Glasses

Calcium fluoroborate glasses doped with trivalent praseodymium ions have been prepared using melt quenching technique with the molar composition (42-x) B2O3 + 20 CaF2 + 15 CaO + 15 BaO + 8 Al2O3 + x PrF3 (x = 0.05, 0.1, 0.5, 1.0, 2.0 and 4.0). Absorption, fluorescence and lifetime spectra were recorded for the title glasses. Judd-Ofelt intensity parameters Ωt (t = 2, 4 and 6) have been determined for the measured oscillator strengths of the absorption bands by including and excluding the 3H4 → 3P2 hypersensitive transition. From the intensity parameters spontaneous emission probabilities (AR), excited state radiative lifetimes (τR) and branching ratios (βR) were calculated. Fluorescence quenching is observed in all the peaks and is explained by energy transfer mechanisms. Using the fluorescence spectra stimulated emission cross section (σe) for all emission transitions have been estimated. Energy transfer processes were also explained to emphasize the quenching of fluorescence intensity of certain emission transition. Based on the results, the utility of Pr3+ doped calcium fluoroborate glasses as laser active materials as well as wave guides in the visible region is discussed.

Optical absorption and fluorescence properties of Dy3+: SFB glasses

This paper presents the preparation and spectroscopic characterization of Dy3+-doped sodium fluoroborate (SFB) glasses of the type (50-x) B2O3 + 25 Na2O + 10 CaF2 + 10 AlF3 + 5 LaF3 + x DyF3 (x = 0.01, 0.1, 0.5,1.0, 2.0 and 4.0 mol%). By measuring the area under absorption bands, the experimental oscillator strengths are determined. The Judd-Ofelt (J-O) intensity parameters Ωλ (λ = 2, 4, 6) are evaluated by the least square fit method. These phenomenological parameters are used to predict luminescence properties of the lanthanide ions in SFB glasses. Photoluminescence spectra and lifetimes of 4F9/2 level of Dy3+ ions in these glasses have been measured by exciting with 348 nm line of xenon flash lamp. The measured decay curves exhibit single exponential at lower concentrations of 0.01, 0.1, 0.5 and 1.0 mol% and non-exponential at higher concentrations of 2.0 and 4.0 mol%. The predicted τR and (βR values of 4F9/2 transition are compared with the experimentally measured values. From the magnitude of stimulated emission cross sections (σe), branching ratios (βm), multiphonon relaxation rates (WMP), the most potential laser transitions are identified and the utility of these glasses as laser active material is discussed.