Ch. Basavapoornima

Efficient Nd3+→Yb3+ energy transfer processes in high phonon energy phosphate glasses for 1.0 μm Yb3+ laser

Efficient Nd3+→Yb3+ resonant and phonon-assisted energy transfer processes have been observed in phosphate glasses and have been studied using steady-state and time-resolved optical spectroscopies. Results indicate that the energy transfer occurs via nonradiative electric dipole-dipole processes and is enhanced with the concentration of Yb3+ acceptor ions, having an efficiency higher than 75% for the glass doped with 1 mol% of Nd2O3 and 4 mol% of Yb2O3. The luminescence decay curves show a nonexponential character and the energy transfer microscopic parameter calculated with the Inokuti-Hirayama model gives a value of 240 × 10−40 cm6 s−1, being one of the highest reported in the literature for Nd3+-Yb3+ co-doped matrices. From the steady-state experimental absorption and emission cross-sections, a general expression for estimating the microscopic energy transfer parameter is proposed based upon the theoretical methods developed by Miyakawa and Dexter and Tarelho et al. This expression takes into account a...

Spectroscopic and fluorescence properties of Sm3+-doped zincfluorophosphate glasses

Abstract Optical absorption and fluorescence spectra of Sm3+-doped zincfluorophosphate glasses with molar composition of 44P2O5+17K2O+9Al2O3+(30–x)ZnF2+xSm2O3 (x=0.01 mol.%, 0.05 mol.%, 0.1 mol.%, 0.5 mol.%, 1.0 mol.%, 2.0 and 3.0 mol.%) referred as PKAZFSm were prepared by melt quenching technique and were characterized through Raman, absorption, emission and decay curve analysis. From the absorption spectra, Judd-Ofelt intensity parameters were determined and were used to predict radiative properties such as transition probabilities (AR), radiative lifetimes (τR), branching ratios (βR), effective bandwidths (Δλeff) and stimulated emission cross-section (σ(λp)) for the excited 4G5/2 luminescent level. The decay curve for the 4G5/2 level was single exponential for lower concentration and became non-exponential for higher concentrations. The non-exponential nature of the decay curves of the 4G5/2 level increased with increase in Sm3+ ions concentration accompanied by decrease in lifetime due to energy transfer processes among the Sm3+ ions. The non-exponential decay curves was well fitted to the generalized Inokuti-Hirayama model for S=6, indicating that the energy transfer among optically active ions was of dipole-dipole interaction. The cross-relaxation mechanism responsible for the quenching of lifetimes and the effect of variation of concentration on the spectroscopic properties were also discussed.

Pressure-dependent fluorescence studies of Sm3+-doped fluorophosphate glass

Pressure-induced luminescence spectra and decay curves for the 4G5/2 level of Sm3+ ions in fluorophosphate glass (PKFBASm 40:54 P2O5+14 K2O+13 BaO+6 KF+9 Al 2 O 3+4 Sm 2O 3) have been measured as a function of pressure up to 36.3 GPa at room temperature. In this pressure range, a red shift of barycenter and Stark level splittings are observed for the 4G5/2→6HJ (J=9/2, 7/2 and 5/2) multiplet transitions. The decay curves of the 4G5/2 level show non-exponential behavior in the entire pressure range, which has been explained by energy transfer due to the dipole–dipole interaction. The effect of releasing pressure on the luminescence spectra and decay curves has also been studied. The results obtained for this glass have been compared with Sm3+-doped fluorophosphate, phosphate, lead phosphate, lithium borate and tellurite glasses.

High pressure luminescence study of Sm3+: K–Ba–Al fluorophosphate glass

The luminescence spectra and decay curves for the 4G5/2 level of Sm3+ ions in 55.95P2O5+14K2O+6KF+14.95BaO+9Al2O3+0.1Sm2O3 glass, referred to as PKFBASm01, have been studied as a function of pressure up to 40.5 GPa at room temperature. With the increase in pressure, a continuous red shift of the 4G5/2→6H9/2, 7/2, 5/2 transitions and a progressive increase in the magnitude of the crystal-field splittings for these transitions are observed. The decay curves for the 4G5/2 level of the Sm3+ ions in PKFBASm01 glass are found to exhibit single exponential behavior at ambient pressure and become non-exponential at higher pressures, accompanied by shortening of lifetimes. A generalized Yokoto–Tanimoto model has been used to explain the pressure-induced non-exponential nature of the decay curves.

Optical Absorption and EPR Studies on Gamma-Ray Irradiated RE 3+ -Doped Fluorophosphate Glasses

We have studied the effect of γ-ray irradiation on optical absorption, emission and decay characteristics of RE3+ (RE = Sm, Eu and Dy)-doped fluorophosphate glasses. Electron paramagnetic resonance (EPR) study confirms the POHC and PO3 EC defects induced in glasses by the γ-irradiation. The presence of induced defect centers significantly affects the optical and emission properties. The optical band gap values of the studied systems increased after the γ-ray irradiation. The phonon energy and electron–phonon coupling strength of Eu3+-doped fluorophosphate glass were determined from the phonon sideband analysis. The emission intensity of the RE3+ ions increased significantly after the γ-ray irradiation. The intensity parameter, R is the ratio of the intensities of the 5D0 → 7F2/5D0 → 7F1 transitions of Eu3+ ion and Y/B intensity parameter is the ratio of intensities of the 4F9/2 → 6H13∕2/4F9/2 → 6H15/2 transitions of Dy3+ ion reveal that the local environment around the RE3+ ion changed after the γ-ray irradiation in the present system. The lifetime of excited states of RE3+ ions decreased after the γ-ray irradiation due to the formation of defects induced by the γ-ray irradiation. The CIE color coordinates were determined before and after the γ-ray irradiation for the Dy3+-doped glass system.

Luminescence and decay characteristics of Tb3+-doped fluorophosphate glasses

ABSTRACT Tb3+-doped fluorophosphate glasses with the composition of P2O5–K2O–SrF2–Al2O3–x Tb4O7 (where x = 0.1, 0.5, 1.0, 2.0 and 4.0 mol%) were prepared by a conventional high temperature melt quenching technique and characterized through absorption, emission, excitation and decay measurements. From the emission studies, a strong green emission at around 546 was observed, which corresponds to the 5D4 → 7F5 transition of Tb3+ ion. Green/blue intensity ratios (IG/IB) were evaluated as a function of Tb3+ concentration and vice versa. Higher IG/IB intensity ratio confirms the higher covalency between Tb–O bond and higher asymmetry around the Tb3+ ions in the present fluorophosphate glasses. The decay curves for the 5D4 level of Tb3+ ion were measured and found that they exhibited single exponential nature irrespective to the dopant concentration. The experimental lifetime was determined using single exponential fitting and found that it increased from 2.65 to 2.95 ms when Tb3+ concentration increased from 0.1 mol% to 4.0 mol%. The derived properties were compared to the other Tb3+-doped glasses in order to see the potentiality of the material for visible laser gain media at 546 nm.

Synthesis and Characterization of Red Emitting Eu3+-Doped YBO3 Phosphor

Red emitting new phosphor, YBO3 doped with Eu3+ ions, has been prepared by solid state reaction method. The excitation spectra were recorded by monitoring a red emission at 610 nm and observed very intense band in the lower wavelength region, 230 ~ 280 nm, which could be attributed due to the Eu3+-O2- charge transfer band (CTB) lying in the band gap region of the host matrix. In addition to the CTB, strong absorption lines in the excitation spectrum is located at 395 nm and 465 nm which corresponds to the 7F0 → 5L6 and 7F0 → 5D2 transitions of Eu3+ ions, respectively. The decay curves are found to be single exponential at lower concentrations and tends to be non-exponential at higher concentrations with shortening of lifetime (2.74 ms to 0.86 ms). The systematic investigation indicates that this Eu3+-doped YBO3 phosphor is an ideal candidate for solid state lighting applications.