Blue Luminescence of Color Centres in Sapphire

Abstract

Due to the excellent physico-chemical and technological properties single crystals of sapphire ( a-A1203) represent serious interest a s promising materials for various applications including optical windows, laser matrixes, etc. In particular, luminescence centres (LC) introduced by radiation o r by thermochemical treatment have been studied and recently a correlation between some of the main bands in the optical spectra and the models of centres has been established /1 to 6/.The clarification of the nature of the LC is especially difficult i f the main luminescence bands of several centres are situated in the same spectral region. Only the use of several different methods then allows one to determine the parameters of the corresponding LC /5, 7 to 9/. Such a situation was encountered in the investigation of the luminescence in the blue-violet region of the spectrumonly the complex measurements of the polarization, decay kinetics, and the excitation spectra allowed to demonstrate that three types of LC have emission bands in the same spectral region /8/: 1'1 F centres (band at 3 . 0 eV) /3, 4/; 2 ) pairs of anion and cation vacancies (band at 2 . 9 5 eV) /l O/; and 3) a type of presumably electronic centre with an emission band at 2 . 8 eV.The present note describes the results of a more detailed study of the luminescence band at 2 . 8 eV. The luminescence was studied on undoped Czochralski-grown crystals a s well as on magnesium-doped (0.035 wt%) Verneuil crystals. Part of the undoped crystals was irradiated with 1 O1 cm-2 reactor neutrons, others were additively colored or annealed in oxygen at 1770 K. Some Mg-doped crystals were also additively colored. The samples were polished platelets measuring 6 x 6~2 mm with the C3 axes parallel or perpendicular t o the platelet. The spectral and polarization characteristics were measured a s described earlier /3, 5, 11/. 3 I ) 8 Kengaraga Street, 226063 Riga, USSR.