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Photoluminescence (PL), radioluminescence (RL), and thermoluminescence (TL) investigation of Y2O3:Bi nanophosphors prepared by solution combustion synthesis using urea, glycine, and hexamethylenetetramine (HMT) as fuels was carried out. The as-prepared nanopowders have increasing crystallinity and average crystallite sizes for urea, glycine, and HMT, respectively. Luminescence is composed of two emission bands centered at 408 and 505 nm due to two nonequivalent Bi3+ sites with symmetry S6 and C2, respectively. The occupancy of these sites depends on the synthesis conditions, in agreement with theoretical predictions. Annealing at 1000 °C for 1 h improves PL and RL efficiency due to enhanced crystallinity of the nanopowders and activation of recombination centers (Bi3+ ions). No shift in the PL peak position was observed as a function of average crystallite size. The concentration quenching was experimentally determined to have a maximum emission of around 3 mol % of the dopant. TL spectra present several peaks between 50 and 300 °C, and the total TL signal is correlated with the heat of combustion of the fuel and thus crystallinity increases. Most likely, increases in RL and TL are also due to the increase in the concentration of recombination centers. [ABSTRACT FROM AUTHOR]

Hydrothermally prepared nanophosphor Y2SiO5:Ce crystallizes in the P21/c structure, rather than the B2/b structure observed in bulk material. Relative to bulk powder, nanophosphors of particle size ∼25–100 nm diameter exhibit redshifts of the photoluminescence excitation and emission spectra, reduced self absorption, enhanced light output, and medium-dependent radiative lifetime. Photoluminescence data are consistent with reduced symmetry of the P21/c structure and are not necessarily related to reduced dimensionality of the nanophosphor. In contrast, medium-dependent lifetime and enhanced light output are attributed to nanoscale behavior. Perturbation of the Ce ion electric field is responsible for the variable lifetime. [ABSTRACT FROM AUTHOR]