Photoluminescence origin in Bi3+ - doped YVO4, LuVO4, and GdVO4 orthovanadates

Steady-state and time-resolved emission and excitation spectra and the luminescence decay kinetics are studied in the 4.2-500 K temperature range for the blue intrinsic emission and the yellow Bi3+ - related emission of YVO4:Bi, LuVO4:Bi, and GdVO4:Bi microcrystalline powders. It is suggested that the Bi3+- related absorption (excitation) band, peaking around 3.75 eV, arises from the electronic transition from the ground (1)S(0 )state of a Bi3+ ion to its excited P-3(1) state located inside the conduction band (CB). The excitation in the Be3+ - related absorption band is suggested to result in an electron release from the P-3(1) level of Be into the CB and its subsequent recombination with the hole remained at the Bi3+ ion. As a result, an exciton localized around the single Bi3+ ion is created. The radiative decay of this exciton is accompanied with the Bi3+ - related 2.12-2.19 eV emission. The origin, structure, and parameters of the exciton states, responsible for the luminescence of the Bi3+ - doped vanadates, and the processes taking place in these states are investigated and discussed. No ultraviolet emission arising from the P-3(1,0) - S-1(0) transition of Bi3+ ions is found. From the afterglow excitation spectra, the band gap energy in the investigated vanadates is estimated to be about 4.20-4.25 eV.