On the origin of cerium-related centres in lead-containing single crystalline films of Y2SiO5 : Ce and Lu2SiO5 : Ce

Absorption, electron spin resonance, and photo- and thermally stimulated luminescence characteristics are studied for single crystalline films (SCFs) of Y2SiO5 : Ce and Lu2SiO5 : Ce prepared by the liquid phase epitaxy method with the use of a PbO-containing flux. They are also compared with the characteristics of the corresponding single crystals (SCs) as well as of the undoped Y2SiO5 and Lu2SiO5 SCFs and SCs. The concentration of stable trivalent Ce3+ ions in various SCFs with different lead and cerium contents is found to be negligible. It is suggested that stable tetravalent Ce4+ ions mainly exist in the SCF due to a large concentration of Pb2+ ions whose excess volume and negative charge can be effectively compensated by relatively small tetravalent Ce4+ ions. Nevertheless, the characteristic Ce3+ emission in the SCFs of Y2SiO5 : Ce and Lu2SiO5 : Ce does appear under photoexcitation in the charge-transfer absorption region (E-exc > 4.2 eV), most probably as a result of the two-photon excitation process. Ce3+ emission is observed under excitation by the ionizing radiation as well and is explained by the recombination of free electrons from the conduction band with Ce4+ ions.