BLUE AND GREEN UP-CONVERSION FLUORESCENCES OF HO3+ IN FLUORIDE GLASSES

Blue and green upconversion fluorescences at about 424, 485, and 545 n m were observed in Ho3+ singly doped fluoride glasses under 647 nm exc itation. The relative intensities of these fluorescences for ZrF4 (HfF 4) based glasses were found to be larger than those for AlF3 based gla sses due to their lower phonon energies. The upconversion efficiency a nd the emission efficiency of Ho3+ doped fluoride systems are primaril y dominated by the populations of the corresponding intermediate level s from which a part of the excited ions can be re-excited to the upper emitting levels. Rate equation modeling of the upconversion fluoresce nce has been established and utilized to reveal the upconversion mecha nisms for the Ho3+ doped systems. Using this model, the concentration and the excitation dependences of these upconversion fluorescences are well interpreted.