Given that Zn ions crystallized in the growth process, the cutoff wavelength was influenced. To further confirm whether Zn2+ existed in the as-grown LBO crystals, transparency spectra were recorded within the range of 120–380 nm. For this measurement, a sample with a thickness of 4.5 mm was cut from the as-grown
LBO crystal and polished to optical grade. Fig. 3 shows the transmission spectra of LBO crystals in the UV region. The UV cutoff wavelength was 160 nm, and a 10 nm red shift was observed for the cutoff wavelength, which was further evidence of the presence of zinc ions in LBO crystals.