Converting Eu3+ between defect sites in BaFCl for persistent spectral hole burning

Persistent spectral hole burning (PSHB) is demonstrated in the F0^{7→D0 5 optical transition of Eu3+ doped into crystals of BaFCl. For Eu3+ ions at two different lattice sites, persistent holes can be burned at temperatures below 77thinspthinspK. The characteristics of the hole-burning process suggest that the observed PSHB effect is due to laser-excitation-induced site-to-site conversion. One type of Eu3+ site is converted into another type of defect site. This process is not optically reversible, and holes can be erased only when the temperature increases to 150thinspthinspK. copyright 1999 Optical Society of America}