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. [ABSTRACT FROM AUTHOR]