Phase precipitation of Yb2+ ions in RbCl monocrystals monitored by optical absorption measurements at elevated temperatures.

Optical absorption spectra of RbCl:Yb2+ crystals have been measured at several elevated temperatures up to 300C. Results showed that in hot RbCl:Yb2+ crystals, the Yb2+ ions occupied lattice sites with effective octahedral, O, point symmetry. Values of an energy parameter , which is an approximate measure of the strength of the crystal field splitting of the 5d electron states of the 4f5d configuration of the Yb2+ ions in an octahedral crystal field,were obtained for the crystals at different temperatures. The variation in the value of with increase in temperature was used to identify three precipitate phases of the Yb2+ ions in the crystal. Type 1 precipitates were identified as I-V dipoles in freshly quenched RbCl:Yb2+ ion - Rb ion vacancy complex. Type II precipitates were tentatively identified as metastable YbCl type precipitates in the RbCl lattice which occur when the RbCl:Yb crystals were heated to temperatures in the range 200- 270C. The third precipitate phase was tentatively identified as the stable YbCl precipitates in the RbCl lattice, which were formed in the temperature range 320 - 360C. Keywords: Phase precipitates, optical absorption spectra, divalent ytterbium, rubidium chloride and variable temperature optical cellNigerian Journal of Physics Vol. 19 (2) 2007: pp. 201-21