Synthesis and photoluminescence of nanocrystalline lutetium pyrosilicate doped with Ce3+

The nanocrystalline Lu2Si2O7:Ce3+ (LPS:Ce) phosphor was obtained as a result of a solid state reaction at 1250 °C of Lu2O3 and SiO2. Compared to the monocrystals grown by the Czochralski method (below 0.5%) the procedure of the synthesis allows much higher level of the activator doping (5%). Two samples, one in air (LPS:Ce–O) and the second one in N2/H2 atmosphere (LPS:Ce–R) were synthesized for comparison. X-ray diffraction analysis confirmed crystallization of a single phase of LPS in the indicated temperature. The UV excited optical luminescence spectrum of LPS:Ce–O at 10 K consists of two wide bands centered at 380 and 407 nm. The positions of the bands and the decay time of 35 ns characteristic for the parity allowed 5d–4f fast emission of the Ce3+ ion. The overlap between a self-trapped (STE) emission of the host (between 320 and 470 nm) and 4f–5d absorption of Ce3+ (centered at 350 nm) allows the energy transfer, which explains the scintillation efficiency of LPS:Ce. Two luminescence mechanisms were detected for the LPS:Ce–R sample. The decay times of 30 ns and 200 μs cannot have the same origin, as they defer too much. According to the tentative explanation the fast emission is a result of the 5d–4f transition of Ce3+ and the slow component of the Ce4+ charge transfer luminescence associated with defects caused by reducing atmosphere.