On the luminescence origin in Y2SiO5:Ce and Lu2SiO5:Ce single crystals

Photoluminescence characteristics of single crystals of Ce3+-doped rare-earth oxyorthosilicates RE2SiO5 (RE: Y, Lu) with different Ce3+ concentrations are studied in the 4.2-500 K temperature range by the steady-state and time-resolved spectroscopy methods. The concentrations of single and dimer Ce3+-related centers of different types in the investigated crystals are evaluated from their EPR spectra. On the basis of the obtained results and analysis of literature data, the origin of the Ce3+-related centers responsible for the luminescence of these crystals is clarified and a new interpretation of their luminescence spectra is proposed. The suggestion is made that the dominating higher-energy (violet) doublet emission band of Y2SiO5:Ce and Lu2SiO5:Ce (denoted earlier as the Ce1 emission) arises from the Ce3+ ions substituting for the host crystal lattice rare-earth RE3+ ions in both RE1 and RE2 lattice sites and, thus, can be considered as the superposition of the strong Ce1 and weak Ce2 emission bands. The weaker lower-energy (blue) broad emission band (denoted earlier as the Ce2 emission) is ascribed to the dimer {Ce3+ - Ce3+} centers. No centers with the local X-1 structure, containing Ce3+ ions and neighboring O-2(-) ions (the CeO9 clusters embedded into the crystal lattice of the X-2 structure), reveal themselves in the EPR spectra.