V^-_F and V⁺_K Aggregate Colour Centres: Origin of the Room-Temperature 350 nm Absorption Band in PbWO₄

A PbWO₄ (PWO) single crystal has been grown by the advanced Bridgman method. The as-grown PWO crystal exhibits a weak band at 350 nm. This band was fitted into two overlapping bands peaking at 330 nm and 360 nm respectively. The absorption spectra of the as-grown crystal sample on un-polarized light and polarized light are measured respectively. The formation mechanism of colour centres in the as-grown PWO crystal is discussed and the 330 nm and 360 nm bands are ascribed to V^-_F and V⁺_K centres respectively. The structure models of V^-_F and V⁺_K centres are illustrated. The configuration terms, absorption transitions between the energy terms, the absorption spectral features on polarized light and the distributions of V^-_F and V⁺_K centres in PWO are systematically studied.