Depletion of high-energy carriers in YAG optical ceramic materials.

The scintillation properties of YAG:Ce transparent ceramic material prepared by a hot-pressing technique have been characterized and compared with those of a chemically identical specimen of single crystal. Each of the scintillation steps (conversion, energy transfer and luminescence) has been selectively investigated using appropriate spectroscopic techniques. The light output from the ceramic specimen was measured at approximately 1500 photons/MeV, only 10% of that from the single crystal. This drastic decrease in the ceramic reflects the inefficient transfer of energy from the excited host to the Ce ion. The inefficiency can be attributed to the presence in the ceramic material of a high population of lattice defects, as demonstrated by the UV absorption spectra. Thermoluminescence experiments show that these defects can serve as sinks for free carriers (electrons and holes), providing sites for their nonradiative recombination and preventing them from conveying their energy to the emitting centers.