Intrinsic chromatic switching of luminescence in Yb/sup 3+/, Er/sup 3+/:CsCdBr/sub 3/

Summary form only given. Previously, we have reported intrinsic instabilities of the luminescent intensity from a variety of Yb-containing compounds. In heavy metal halides, this phenomenon has been explained as a manifestation of driven local field effects in dense radiation systems. While earlier observations revealed abrupt changes in luminescent intensity under quasi-static conditions, no abrupt changes in the wavelength of the emitted light were found. Here, we report the first observations of intrinsic chromatic instabilities that accompany bistability of the luminescent intensity in a multi-ion system. For our experiments, randomly-oriented samples of crystals of Er,Yb:CsCdBr/sub 3/ were cooled by direct contact with flowing helium vapor to the range 4-40 K, and subjected to weakly-focused radiation from a Ti:sapphire laser tuned to the vicinity of Yb absorption features at 943 nm with a 2-plate birefringent filter. No detectable upconversion emission was generated with pump light tuned to 943 nm in crystals lacking the Yb sensitizer. However, the co-doped sample produced intense upconversion when excited at this wavelength, indicating that visible upconversion takes place through cooperative sensitization of Er luminescence by Yb in this host crystal.