L. Rama Moorthy

Spectral investigations on Dy3+-doped transparent oxyfluoride glasses and nanocrystalline glass ceramics

Dysprosium-doped oxyfluoride glasses and nanocrystalline glass ceramics have been synthesized and studied by x-ray diffraction, absorption, and visible and near-infrared emission spectra. The samples emit intense white light when populating the F49/2 level with a 451 nm laser light and, from the visible emission spectra, yellow to blue intensity ratios and chromaticity color coordinates have been calculated and their relative variation have been discussed based on the concentration of Dy3+ ions and the heat treatment conditions used to prepare the glass ceramics. Infrared emission has also been observed in glasses and glass ceramics after laser excitation at 800 nm, showing bands at 1.33 and 1.67 μm, useful for optical amplification in fiber amplifiers.

A study on fluorescence properties of Eu3+ ions in alkali lead tellurofluoroborate glasses

Abstract Glasses with chemical composition of (in mol.%): 26 RF-20 PbO-10 TeO2–43 H3BO3–1 EuO3 (RLTB) were prepared by conventional melt quenching method. The Judd-Ofelt intensity parameters Ω2 and Ω6 were obtained from the absorption intensities of 7F0→5D2 and 7F0→5L6 transitions, respectively. In order to overcome the problem of applicability of Judd-Ofelt analysis at room temperature due to the overlapping of the transitions originating from 7F0 and 7F1 levels of Eu3+ ion, the effect of the thermalization on the population of energy levels was taken into account. The photoluminescence spectra contained five emission bands originating from the 5D0 metastable state to 7FJ(J=0, 1, 2, 3, 4) lower lying states. The decay profiles were found to be single exponential in all the three glasses. The measured lifetimes (τmes) were in good agreement with the calculated lifetimes (τcal) obtained by using the thermally corrected Judd-Ofelt intensity parameters.

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.

Spectroscopic investigation and optical characterization of Eu3+ ions in K–Nb–Si glasses

This paper reports on the effect of concentration of Eu(3+) ions in K2O-Nb2O5-SiO2-Eu2O3 (KNbSiEu) glasses prepared by the melt quenching technique. By using the Judd-Ofelt (JO) theory, the intensity parameters Ωλ (λ=2, 4, 6) have been determined from the absorption and emission spectra of Eu(3+) ions under different constraints. The radiative properties of some of the excited states of Eu(3+) ions have been calculated. The decay curves of (5)D0 level exhibited single exponential for all the Eu(3+) ions concentrations. From these results, it is suggested that the strong red emission at 616 nm corresponding to the (5)D0→(7)F2 transition could be used for the development of optical display devices.

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.

Absorption and emission characteristics of Er3+ ions in alkali chloroborophosphate glasses

Alkali chloroborophosphate glasses containing 1 mol% of Er3+ ions were studied experimentally using the absorption and emission spectroscopy. The energy level scheme for the 4f11 (Er3+) electronic configuration was deduced from the observed band energies of the absorption spectra in terms of a parametrized Hamiltonian using the various free-ion spectroscopic parameters. Oscillator strengths (f) measured from the absorption spectra have been analyzed using the Judd-Ofelt theory to evaluate the three intensity parameters omegalambda (lambda = 2, 4 and 6). Reasonable agreement between the measured and calculated f values has been found. Electric and magnetic dipole transition probabilities, fluorescence branching ratios, integrated emission cross sections and radiative lifetimes were calculated for all the excited states of Er3+ ions. The non-radiative (WNR) relaxation rates from the excited levels to the next lower levels have been calculated and the relationship between the energy gap and non-radiative relaxation rate has been established. These results were used to predict the possible potential laser transitions in Er-doped alkali chloroborophosphate glasses.

Optical spectroscopy, 1.06 μm emission properties of Nd3 +-doped phosphate based glasses

Neodymium doped phosphate based glasses with composition of (P2O5+K2O+Al2O3+CaF2) were prepared. The samples were analysed through differential thermal analysis (DTA), Fourier transform infrared (FTIR), absorption, emission and decay measurements. Judd-Ofelt parameters (Ωλ) have been determined from the spectral intensities of absorption bands in order to calculate the radiative parameters like radiative transition probabilities (AR), radiative lifetime (τR) and branching ratios (βR) for the 4F3/2→4I11/2 laser transition of Nd3+ ion. The effective emission bandwidths (Δλeff), experimental branching ratios (βexp) and stimulated emission cross-sections (σe) have been determined from the emission spectrum. The decay curves of the 4F3/2 level exhibited almost single exponential nature for all the Nd3+ ion concentrations.

Optical absorption spectrum of Pr3+ in aprotic POCl3:SnCl4 laser liquid

Abstract Spectral studies of Pr3+ in aprotic POCl3 + SnCl4 laser liquid have been carried out in the visible and near i.r. regions. From the observed band positions, the Slater-Condon (F2, F4, and F6), configuration interaction (α, β), spin-orbit (ξ4f), nephelauxetic (β), bonding (δ), and Judd-Ofelt (T2, T4 and T6) intensity parameters are evaluated. From the splittings of the 3P2 and 1D2 bands, crystal field (A20, A40) parameters were evaluated assuming C3h symmetry for Pr3+ in POCl3:SnCl4 laser liquid. Theoritical estimates of spectral intensities calculated from Judd-Ofelt and electric (Sed)-magnetic (Smd) dipole line-strength methods are in good agreement with the observed values. Radiative lifetimes (TR) for the electronic excited states 3P1, 3P0 and 1D2 of Pr3+ in POCl3:SnCl4 laser liquid are predicted.

Luminescence properties of Eu3+-doped Na3Gd(PO4)2 red-emitting nanophosphors for LEDs

Eu(3+)-doped Na3Gd(PO4)2 phosphors were synthesized by the modified citrate gel combustion technique. From the XRD pattern, structure of the compound was found to be orthorhombic with a particle size of 10-20nm. The emission spectra revealed that the Na3Gd(PO4)2:Eu(3+) phosphors can be excited effectively by 394nm pump wavelength. From the concentration dependent photoluminescence studies, the optimum concentration for efficient luminescence of Eu(3+) ions in Na3Gd(PO4)2 phosphor has been found to be 1.5mol%. Decay curves of the (5)D0 level of Eu(3+) ions were recorded by monitoring the emission at 596nm corresponding to (5)D0→(7)F1 transition and are found to be single exponential for all the concentrations. The chromaticity properties for different concentrations of Na3Gd(PO4)2:Eu(3+) nanophosphors were calculated from emission spectra and analyzed in the frame work of CIE color diagram.

Structural and luminescent properties of KY(1-x)DyxBO3 phosphors.

Yttrium borate phosphors (KY(1-x)DyxBO3) doped with Dy(3+) ions were synthesized by the solid-state reaction method. The structural and morphological characteristics were studied by XRD, FTIR and SEM measurements. Luminescent properties of different concentrations of KY(1-x)DyxBO3 phosphors were investigated from the excitation, emission and decay analyses. The emission spectra exhibited characteristic blue (460-500nm) and yellow (555-610nm) bands of Dy(3+) ions which combines to give white light. The evaluated color co-ordinates (x, y) were found to lie within the white light region of CIE chromaticity diagram. All the decay curves of Dy(3+) ions exhibited non-exponential nature and the experimental lifetimes for the (4)F9/2 excited level were found to decrease from 0.87, 0.47, 0.35, 0.26 and 0.13ms with the increase of Dy(3+) ion concentrations from 0.05, 0.1, 0.15, 0.2 and 0.3mol%, respectively. In order to understand the energy transfer mechanism, the decay curves were fitted to Inokutti-Hirayama model and found that the energy transfer is of dipole-dipole type. From the results of these investigations, it is concluded that the KY(1-x)DyxBO3 phosphors are more useful for white light emitting diodes.