Thangaraj Selvalakshmi

Investigation of defect related photoluminescence property of multicolour emitting Gd2O3:Dy3+ phosphor

Multicolour emitting Gd2O3:Dy3+ phosphor is prepared by citrate based sol–gel method as a function of annealing temperature of the sample and its emission property dependence with lattice defects is elaborated. The annealed phosphors are characterized by X-ray powder diffraction (XRD), Raman spectroscopy, diffuse reflectance spectroscopy (DRS), photoluminescence (PL), fluorescence lifetime and positron annihilation lifetime spectroscopy (PALS). The phosphors annealed at different temperatures greatly influence the defect and emission intensities, as revealed from PL and PALS measurements, respectively. The efficient energy transfer (ET) from the Gd3+ ion to Dy3+ ion is schematically illustrated with the aid of an energy level diagram. The PL spectra clearly conclude that Dy3+ with an ionic radius close to the Gd3+ ion prefers to occupy the C2 site in the Gd2O3 matrix. The positron lifetime spectroscopy qualitatively explains the concentration of defects (vacancy and voids) which are minimized with the increase in the annealing temperature. The correlation between PL emission and lattice defects is also reported in detail.

Structural, optical and electrical properties of GdAlO3:Eu3+Ba2+

Effect of Ba2+ ions concentration on the photoluminescence of GdAlO3:Eu3+ Ba2+ phosphor is investigated. The phosphors are synthesized by citrate-based sol-gel method and the formation of orthorhombic phase GdAlO3 is confirmed by XRD analysis. Kubelka-Munk function is used to estimate the band gap and the value varies with concentration of Ba2+ is observed. Photoluminescence spectra show a strong red emission peak at 616 nm corresponding to5D0→7F2 transition and its intensity increase with the addition of Ba2+ ions. The presence of Eu3+ and Ba2+ ions in GdAlO3 strongly influences the dielectric property of GdAlO3.

Optical Study on Gadolinium Oxide Nanoparticles Synthesized by Hydrothermal Method

Cubic phase gadolinium oxide nanoparticles were prepared by hydrothermal method at various reaction temperatures like 60 °C, 120 °C, 180 °C and 240 °C. X-ray Diffraction (XRD) studies confirmed the formation of cubic phase Gd2O3. The broadening of XRD peak, due to crystallite size was investigated with the aid of gaussian and voigt peak fitting function and its comparisons were also performed. Crystallite size calculated from Scherrer formula for Gd2O3 nanoparticles for various reactions temperatures varies between 21 nm and 39 nm. Thermal analysis of as-prepared sample was done and the decomposition temperature was found to be 433 °C for the formation of Gd2O3. The metal-oxygen band in Fourier Transform Infrared Spectroscopy (FTIR) spectra confirmed the presence of Gd2O3. Band gap studies from Diffuse Reflectance Spectroscopy (DRS) revealed the decrease in band gap with respect to the increase in crystallite size. In Photoluminescence (PL) spectra, a broad ultra violet emission is observed between 320 nm and 400 nm. Irrespective of reaction temperature, Scanning Electron Microscopy (SEM) images reported the formation of nanorods.

Photoluminescence and energy transfer process in Gd2O3:Eu3+, Tb3+

Variation in photoluminescence (PL) properties of Eu3+ and Tb3+ as a function of co-dopant (Tb3+) concentration are studied for Gd2-x-yO3: Eu3+x Tb3+y (x = 0.02, y = 0.01, 0.03, 0.05). The crystal structure analysis is carried out by X-ray Diffraction (XRD). Absence of addition peaks corresponding europium or terbium phase confirms the phase purity. Diffuse reflectance spectroscopy (DRS) reveals the absorption peaks corresponding to host matrix, Eu3+ and Tb3+. The bandgap calculated from Kubelka – Munk function is also reported. PL spectra are recorded at the excitation wavelength of 307 nm and the emission peak corresponding to Eu3+ confirms the energy transfer from Tb3+ to Eu3+. The agglomeration of particles acts as quenching centres for energy transfer at higher concentrations.

Photoluminescence and energy transfer study on Gd2O3:Eu3+, Al3+

A strong red light emitting Gd2O3:Eu3+, Al3+ phosphors are prepared by sol-gel process at various annealing temperature. The structural properties are deduced from XRD pattern. The excitation and emission spectra explained the photoluminescent properties of Gd2O3:Eu3+, Al3+. The excitation spectra contained peaks corresponding to charge transfer and 4f-4f transition of Gd3+ and Eu3+. The phosphor exhibits energy transfer process from Gd3+ to Eu3+. Under the excitation of 254 nm, a strong red emission peak is observed at 611 nm which has been assigned to 5D0→7F2 transition and its intensity increases with annealing temperature upto 700 °C. A non-uniform spherical like morphology is observed for the phosphors in the SEM.

Structural, optical and morphological study on Gd 2 O 3 :Eu 3+

Eu3+ doped Gd2O3 phosphors were synthesized successfully by sol-gel method. The growth of particle was inhibited with the addition of surfactant PEG. The formation of cubic phase Gd2O3 was confirmed from XRD pattern. The reflectance spectra exhibited the absorption peaks corresponding to the dopant and host ions. The excitation spectra showed a broad peak at 248 nm corresponding to ligand to metal charge transfer. A sharp red emission peak at 611 nm indicated the presence of more number of Eu3+ ions in non-inversion symmetry site. The SEM micrograph showed the growth of agglomerated and non-uniform shaped particles with the addition of PEG.

Effect of dopant concentration on photoluminescence properties of Gd2O3:Eu3+

Red-emitting Gd2-xO3:Eux3+(x = 2,4,6at%) was synthesized by sol-gel method and its optical properties were studied. The formation of Gd2O3 and the presence of metal oxygen bond were confirmed from X-ray diffraction (XRD) and fourier transform infrared (FTIR) spectroscopy studies. Incorporation of Eu3+ in Gd3+ site was proved qualitatively by Energy dispersive X-ray analysis (EDX). A strong charge transfer band (CTB) at 254 nm was observed in the excitation spectra with varying intensity for different dopant concentrations. Photoluminescence (PL) spectra reported red emission peak at 611 nm corresponding to 5D0-7F2 transition between Eu3+ energy levels. Concentration quenching occurred at 2 at % and its critical distance was calculated. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) studies was carried out to study the morphological variations.