Induced Absorption Phenomena, Thermoluminescence and Colour Centres in KMgF₃, BaLiF₃and LiCaAlF₆Complex Fluorides

Abstract

KMgF 3 , BaLiF 3 and LiCaAlF 6 (LiCAF) single crystals were grown by the Czochralski method under CF 4 atmosphere. X-ray irradiation was used to carry out a comparative study of induced optical absorption phenomena and colour centre creation in the vacuum-ultra-violet (VUV), ultra-violet and visible spectral regions. In the case of LiCAF, the X-ray induced absorption peak at 262 nm can be ascribed to F centre. The integral of the induced absorption spectra is significantly lower in LiCAF with respect to the other studied materials; moreover, LiCAF shows stable VUV transmission characteristics and the most resistant surface toward what is regarded as the damage due to reaction with air atmosphere.

VUV spectroscopy of pure and Tm3+-doped LicaAlF6 crystals

“…The weaker bands around 500 nm have an extrinsic origin (defects and/ or unintentional impurities); they are well excited in the transparency range of the LICAF crystal. This interpretation is supported by investigation of radioluminescence spectra of high-purity LiCAF crystal at room temperature (RT) [19], and similar emission bands have been observed in the thermoluminescence spectra after X-ray irradiation [20]. Fig.…”

VUV spectroscopy of Tm3+ and Mn2+ doped LiSrAlF6

“…LiCAF is found to be very stable concerning the creation of X-ray induced colour centres as well as the gradual surface damage in air [3]. LiCAF and LiSAF crystals are transparent up to 112 and 116 nm, respectively [4].…”

Color centers in BaMgF 4 crystals

“…It should be noted that the one of them (268 nm) is similar to the F-band position in a LiBaF 3 crystal (~ 266 nm). V k , F, and F n bands were determined in LiBaF 3 earlier [4,8,9]. The color centres luminescence spectra of BaMgF 4 and LiBaF 3 are similar (Fig.…”

“…This equation gives the reasonable values for the F-band location for KMgF 3 , NaMgF 3 and LiBaF 3 crystals [4,7,8]. The distances between Mg 2+ and F − in a tetrahedron are equal to 1.9340, 1.978 and 2.0149 Å in BaMgF 4 .…”