UP-CONVERSION FLUORESCENCE OF HO3+ IONS IN A BAF2 CRYSTAL

Efficient upconversion luminescence from the Ho3+ C-3v centre in a BaF 2 crystal is reported. The red-to-green and red-to-blue upconversion i s observed upon pumping with a single cw red dye laser. The upconversi on mechanism is assigned as a sequential two-photon excitation process in which the excitation wavelength is resonant with either ground sta te absorption (GSA) or excited state absorption transitions. The effic ient green upconversion with excitation into GSA results from a double -resonant excitation between the I-5(8) --> F-5(5) and I-5(7) --> F-5( 3) transitions. (C) 1998 Elsevier Science B.V. All rights reserved.