Effects of monochromatic UV radiation on the thermoluminescence of annealed KBr:Cu+ crystals

Effects of monochromatic UV radiation on the thermoluminescence glow curve of annealed KBr:Cu crystals have been studied at low temperature. The crystals were irradiated at 20K and heated up to 300K at a rate of 0.1Ks−1, approximately. For all the irradiation wavelengths used, the glow curves consist of two peaks around 170 and 270K. Their intensities have been observed to depend on the wavelength of irradiation. Both emissions resulted to be more intense when the irradiation wavelengths was near the absorption peak of the Cu+ ion or near the band to band absorption of CuBr. Their intensities increase with increasing annealing time. The results are explained in terms of the formation of CuBr nanoparticles during the annealing treatment. The thermally stimulated recombination luminescence appears to be associated to the 3d94s-3d10 transitions of the Cu+ ion. So two possible mechanisms of the e-h pair formation could be used to explain the results: ionization of Cu+, Cu+ → Cu2+ + e, or ionization of halogen ions that are within the CuBr as Br¯ → Br0 + e. In the first case, the recombination luminescence is obtained from the trapping of electrons by the Cu2+ ions, while in the second case, the e-h recombination energy would be transferred to the Cu+ ions.