Probing structural and photophysical features of Eu3+ activated NaCdPO4 orthophosphate phosphor.

Abstract

A series of Eu3+ doped NaCd1-xPO4: x Eu3+ (0≤x≤0.1) phosphors were synthesized and a systematic investigation of structural, morphological, optical and photophysical properties were carried out. Structural characteristics were analyzed both qualitatively as well as quantitatively to establish the phase purity, supported by FTIR and Raman spectroscopy methods. The valance state of the dopant, as well as surface elemental compositions were investigated by XPS technique. The optical characteristics were analyzed by employing UV-Visible DRS, which shows that the host bandgap is getting broadened upon doping as a result of the Burstein-Moss (BM) effect. Eu3+ doped phosphor exhibits emissions rich in red (617nm) under suitable excitations at 393nm while the optimal doping concentration was found to be around x=0.06. The effective non-radiative transfer of energy from host to activator is governed by the dominant dipole-dipole transitions. The hypersensitive transition line 5D0→7F2 is observed owing to the induced electric dipole (ED) transition of Eu3+ centered at 617nm. Local site symmetry has been analyzed to ascertain the environment around Eu3+ and presence of any non-equivalent cation sites. The concentration quenching effect of phosphors was explained on the basis of Dexter's theory and charge compensation mechanism. The Commission Internationale de l'Eclairage (CIE 1931) chromaticity coordinates for the prepared phosphors were estimated and found to lie in the red region of color space. The photoluminescence decay time was measured for the most intense emission line 5D0→7F2 at 617nm under 393nm excitation and the results indicate that Eu3+ activated NaCdPO4 can be a suitable red phosphor for white LED using UV-LED chip owing to it's near UV-excitation characteristics.