Spectroscopic investigation of Ce3+/Eu3+ co-doped Li2BaZrO4 nanocrystalline phosphors

Abstract

This work reports on a one-pot synthesis of Li2BaZrO4 co-doped with Eu3+ and Ce3+ ions using solution combustion method at low temperature. The influence of fixing either the concentration of activator ion or sensitizer ion constant while varying the concentration of the other was investigated. Three concentrations where considered 0.005, 0.02 and 0.04 in mole % ratio. The concentration of the fixed ion was at 0.02. X-ray diffraction results show that Li2BaZrO4 sample prepared with concentration of Ba/Zr ratio of 1 and Ce3+-singly doped sample both display cubic perovskite structure of BaZrO3. Li2BaZrO4 sample with excess Ba3+, Eu3+ singly-doped sample and all co-doped samples have mixed phases of Ba(NO3)2 and BaZrO3. The band gap energy decreased with increasing concentration of dopant or co-dopant ions indicating the introduction of more defects in the band gap. Photoluminescence emissions for all the doped samples at room temperature are entirely from intraconfigurational Eu3+ emission lines when excited at 254 nm, but contain a broad band associated to the Ce3+ ions under indirect excitation at 373 nm. The dominance of the magnetic dipole transition in the entire spectra for all Eu3+ doped samples is a confirmation of the centrosymmetry around the ion. The emission intensity from the co-doped samples with fixed concentration of Ce3+ ion (sensitizer) is 4-folds of magnitude stronger than for corresponding samples with fixed Eu3+ (activator) concentration. Thus, in co-doping, the concentration of the sensitizer should be fixed while that of the activator varied if enhanced emission intensity is desired.