Resonance photoemission in pure and Tb doped CePO4 luminescent nanowires

Abstract

The resonance photoemission spectroscopy (RPES) studies on pure and Terbium doped CePO4 nanowires (NWs) are reported here with the supporting characterizations using structural, optical and morphological properties. The NWs with varying Terbium (Tb) doping concentrations were synthesized using chemical synthesis route. Photoluminescence (PL) showed high PL emission intensity in the visible wavelength range indicating strong green luminescence due to efficient Ce3+ to Tb3+ energy transfer. The PL intensity increased up to a doping concentration of 15 wt% Tb3+, beyond which it decreased due to concentration quenching or cross-relaxation effect. Based on PL studies, pure, 5 wt% (the lowest doping amount) and 15 wt% (that shows the highest PL) doped samples were chosen for RPES studies. To understand the comparative contribution of Ce3+ and Ce4+ in the valence band, RPES measurements performed around the Ce 4d →4 f resonance threshold indicated strong presence of Ce 4 f states in pure CePO4 NWs, which reduced upon 5 wt% Tb doping in CePO4 NWs. At 15 wt% Tb3+ doping, the sample did not show resonance of Ce 4 f feature, which may be because Tb3+ ions have replaced Ce3+ ions in the CePO4 lattice. The results are crucial to understand the relative participation of Ce3+ and Ce4+ oxidation states in the valence band, which is an important factor in defining the optical properties of the material that determine the PL intensity.