Deep-UV absorption study of nonlinear optical crystal KBe2BO3F2

KBe2BO3F2 (KBBF) crystals have some extrinsic absorption in the deep-UV region around 150–160 nm and the reason was unknown. In this paper, undoped KBBF and Cu2+-doped KBBF crystals were grown for the investigation of the extrinsic deep-UV absorption behaviors. The samples were characterized by the transmission spectra, electron paramagnetic resonance (EPR) and photoluminescence spectra (PL). The impurity contents were measured by the inductively coupled plasma-atomic emission spectrometry (ICP-AES). Transmission spectra showed a red shift of about 5 nm in Cu2+-doped KBBF crystals compared with undoped ones. EPR signals only occurred in the spectra of Cu2+-doped KBBF crystals. Photoluminescence spectra showed emission bands at 416 nm and 441 nm which were identified as emission of Cu2+ions with an excitation wavelength of 380 nm. The fluorescence intensity of the Cu2+-doped samples is about 3–4 times higher than that of undoped ones. The above results reveal that Cu2+ ions are possible to enter into the crystal lattice and cause the deep-UV absorption.