Длинноволновый край фундаментального поглощения кристаллов боратов лития LiB-=SUB=-3-=/SUB=-O-=SUB=-5-=/SUB=- и Li-=SUB=-2-=/SUB=-B-=SUB=-4-=/SUB=-O-=SUB=-7-=/SUB=-

Abstract

We have carried out an experimental study of the VUV edge of the optical host absorption of lithium borate crystals LiB3O5 (LBO) and Li2B4O7 (LTB). The transmission (T = 293 K) and absorption (T = 80, 293 K) spectra are studied, the short-wavelength boundary of the transparency band (cutoff wavelength) and the energy position of the edge are determined. fundamental absorption at which the absorption coefficient is k = 50 cm-1. The transmission (T = 293 K) and absorption (T = 80, 293 K) spectra were studied, the short-wavelength edge of the transparency band (cutoff wavelength) and the energy position of the edge fundamental absorption at which the absorption coefficient k = 50 cm-1 were determined. The absorption edge temperature shift coefficient −(3–4.7)·10-4 eV/K was determined. The dependence of the absorption edge parameters of oriented LBO ⊥ Y and LBO ⊥ X crystals has been studied. Based on low-temperature reflection spectra (T = 10 K, θ = 17◦, E = 4–32 eV) the Kramers – Kronig method was used to calculate the spectra of optical constants: refractive index (n) and absorption index (k), real (ε1) and imaginary (ε2) parts of the complex permittivity, as well as the absorption coefficient μ. The lowest energy peak, due to electronic transitions from the top of the valence band to the states of the bottom of the conduction band, was studied in the ε2(E) spectrum, the thresholds for interband transitions were determined (Eg at T = 10 K): 8.5–8.6 eV (LBO ⊥ Y), 8.6–8.7 eV (LBO ⊥ X) and 8.8–8.9 eV (LTB). The origin of the fundamental absorption edge of lithium borates is discussed.