The transmittance and absorption spectra α-Al2O3 monocrystals (sapphire) in the vacuum ultra-violet (VUV) region (hv > 6.0 eV) are analyzed and the lowest absorption level is achieved (k ≦ ≦ 1 cm−1 in the whole VUV region). Using Smakula's formula the conccentration of the possible Cr3+ impurity (5 × 1015 cm−3) or anion vacancies (7.5 × 1015 cm−3) in the investigated sapphires is estimated. Some VUV spectra of radiation-coloured sapphires are presented.
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Abramov et al. (1978) studied this question.
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