Study of thermally stimulated luminescence from different phases of lithium borate and its application in crystal characterization

Single crystals of LiB3O5 (135) have been grown by top-seeded solution growth technique using a self-flux composition. Here, seeding with a platinum wire results in the growth of crystals having an opaque central region and transparent outer portion. Powder XRD measurements revealed the presence of Li2B8O13 as a minor fraction in the translucent portion. For both regions, UV-excited luminescence has been observed, which is related to the presence of impurity. Thermally stimulated luminescence (TSL) from 135 and the other two phases namely Li2B4O7 (247) and Li2B8O13 (2813) co-existing with 135 phase in the Li2O–B2O3 system has been investigated. The glow curves of polycrystalline 2813 and 247 showed the presence of two characteristic glow peaks but at different temperatures, while for 135 only one glow peak was observed. The measurements performed on 135 single-crystal samples taken from different regions of an ingot showed that the transparent portion of the crystal contains an impurity phase in minute amount, which is below the detection limits of the XRD measurement. This study shows that TSL can be gainfully used to detect the presence of a minute amount of impurity phase in 135 crystals.