SITE-SELECTIVE UP-CONVERSION IN HO3+ DOPED FLUORITE CRYSTALS MF2 (M=CA,SR,CD)

With tunable dye laser (620-660 nm) excitation, the site-selective upc onversion properties of 0.1 mole% Ho3+ doped CaF2, SrF2 and CdF2 monoc rystals were studied at 77K. Three distinct luminescence centres (C4v, C3v and cluster) were identified for both CaF2 and SrF2 crystals, whe reas only one cluster centre was detected for CdF2. The upconversion m echanism for the isolated Ho3+ single site (C4v or C3v) is different f rom that for the cluster centre, with a two-step excitation process fo r the former and an energy transfer process for the latter.