Optical absorption and luminescence induced by x rays in KDP, DKDP, and ADP

Abstract

The effect of x-ray irradiation on the absorption and luminescence spectra of KDP, DKDP, and ADP has been investigated. σ-Polarized absorption bands at 390 and 550 nm are induced by low temperature irradiation in the three crystals. A π-polarized band has also been observed in KDP and DKDP peaked at 510 and 550 nm, respectively. Thermal bleaching of the σ bands takes place at ∼70 K for KDP and ADP and ∼105 K for DKDP. π bands annihilate at the Curie temperature Tc for both KDP and DKDP. The experimental data allow association of the σ and π bands, respectively, with the radicals B and A, which have been previously identified by EPR. The same x-ray induced luminescence bands have been observed for the three crystals during low temperature (∼10 K) irradiation. At higher temperatures some differences arise. In particular, a luminescence band appears at 350 nm in KDP and DKDP irradiated at T≥70 K which reaches maximum efficiency at Tc. For ADP only the low temperature emissions are detected up to Tc, where they become quenched. Thermoluminescence glow peaks have been observed at ∼70 K (for the three crystals) and at Tc for KDP and DKDP. Tentative mechanisms are discussed to account for the radiation-induced production of centers, their annihilation behavior, and the light emission. For KDP the effect of impurity doping on these processes has been investigated.