SITE-SELECTIVE SPECTROSCOPY OF HO3+KYF4

Site-selective photoluminescence spectroscopy of Ho3+ ions in single-c rystal KYF4, measured with a Fourier-transform spectrometer at 80 and 2 K sample temperatures, gives evidence for two dissimilar classes of crystal-field sites. Three similar sites contribute to each class givi ng a total of six sites in agreement with recent crystallographic resu lts. Analysis of crystal-field splittings indicates that only one of t he classes can contribute to Yb-->Ho upconversion green lasing in (Yb, Ho):KYF4.