New emerging high-energy radiation detection techniques are based on the use of rare-earth ion doped materials. There is a great demand for new inorganic scintillators for medical applications, including X-ray and g radiation detection. In these applications, the new scintillating materials must comply with the main requirements such as high optical quality, high light yield, short response time etc. Materials satisfying these requirements include Gd3Al2Ga3O12:Ce (GAGG : Ce) scintillating single crystals. By now the optical characteristics of GAGG : Ce have been studied insufficiently. We have therefore measured the spectral reflectance and transmittance characteristics of these crystals using optical spectroscopy in the 200–750 nm range. We have also measured the absorbance and refractive indices and the extinction coefficients, and assessed the optical band gap for GAGG : Ce crystals. For measuring the refractive indices, we have used two spectrophotometric methods, i.e. by the measured Brewster angle and by the reflectance for low incidence angles, i.e., close to the normal. Based on the results we have drawn up the dispersion functions of the refractive indices.
The transmittance spectra of the Gd3Al2Ga3O12:Ce scintillating single crystals in the 200—750 nm range were obtained. The absorbance and extinction spectral functions were calculated based on the experimental spectral curves. The extinction coefficient of Gd3Al2Ga3O12:Ce is within the 10-6–10-4 range. The optical band gap of the Gd3Al2Ga3O12:Ce single crystals was estimated by means the Tauc method is 5.88 ± 0.05 eV. The refractive indices were calculated from the spectral angle reflectance functions for p-polarized light using the Brewster method and from the reflectance spectra for a low incidence angle (6 arc deg) close to the normal (the R0 method). The results obtained using the two methods are in a good agreement.
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