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Effect of Optical and Thermal Bleaching on the uv Bands in Highly Pure and Mn-Doped KCl Crystals

1968; American Institute of Physics; Volume: 176; Issue: 3 Linguagem: Inglês

10.1103/physrev.176.1089

1536-6065

P. C. Mehendru, Ved Mitra,

Thermal properties of materials

In highly pure KCl crystals, \ifmmode\times\else\texttimes\fi{} irradiated at room temperature (RT), the usual uv absorption bands at 212 and 230 nm are observed. The peak position of the 212-nm band when bleached with uv light shifts gradually to 195 nm, without any appreciable change in the intensity of this band. On thermal bleaching (in the range RT to 150\ifmmode^\circ\else\textdegree\fi{}C) in the dark, the position and the intensity of the 212-nm band remain unchanged. When bleached thermally or optically with uv light, the peak position of the 230-nm band remains unaltered, whereas its intensity decreases. In uncolored KCl: Mn crystals, Mn introduces two uv absorption bands at 201 and 273 nm, having half-widths 0.36 and 0.15 eV, respectively. On \ifmmode\times\else\texttimes\fi{} irradiation, the positions, intensities, and half-widths of these absorption bands remain unaltered, and a new absorption band at 223 nm appears. The intensity and half-width of the 223-nm band increases up to 25 h of \ifmmode\times\else\texttimes\fi{} irradiation. Although thermally unstable, the centers responsible for the 223-nm band are fairly resistant to uv-light bleaching. An activation energy ${E}_{a}=0.54\ifmmode\pm\else\textpm\fi{}0.02$ eV is obtained for the thermal bleaching of the centers that absorb in the 223-nm band. Qualitatively, the 223-nm band is similar to the $D$ bands observed by Ishii and Rolfe.