The F-type centres in YAG crystals

The comparative study of optical properties of thermochemically reduced undoped YAG (Y3Al5O12) crystals is reported. A particular type of the centres often observed in YAG crystals synthesized as well as treated under the reducing atmosphere is related to an anion vacancy with one or more trapped electrons (F-type centres in YAG crystals). The changes of photoluminescence intensity and absorption bands intensity of the observed centres under X-irradiation support the F- and F+-centre models. It is shown that the F-centre absorption involves at least two bands, at 195 nm and 240 nm, where the broad F-centre luminescence band at 460 nm can be excited. It is suggested the existence of the F- -centre could be connected with the absorption bands at 360 nm, 480 nm, and 830 nm.