Low-temperature fluorescence in sapphire

UV luminescence of F‐centers in aluminum oxide

“…The absence of polarization or a weak polarization of the optical absorption (OA) of the F-center at 6.05 eV [2,3] and a considerable anisotropy [1,2] of its luminescence at 3 eV confirms the supposition [2], which is based on a long-time decay of the luminescence, about the triplet-singlet origin of the radiative transition. Some experimental facts, which are related to the luminescence near 3 eV, have not been explained so far.…”

“…The position of the maximum at 5.7 eV depends on the temperature and at T = 80 K it is displaced to 5.8-5.9 eV. (2), and luminescence excitation (3) at E em = 3 eV; b -time-resolved spectra (1, 2 − δt 1 = 1.2 ns, ∆t 1 = 5.9 ns; 3 − δt 2 = 23 ns, ∆t 2 = 111 ns) of luminescence excitation with E em = 3 eV at E ⊥C 3 (1,3) or E || C 3 (2,3) Figure 1b presents time-resolved excitation spectra at T = 295 K for two orientations of the sample relative to the SR electric field vector E (E⊥C 3 and E||C 3 ). The fast component (curve 1) at E⊥C 3 replicates the stationary excitation spectrum and includes bands with E ex1 = 5.7 eV, E ex2 = 6 eV and E ex3 = 6.3 eV.…”

“…For example, it was found [4] that the kinetics of the luminescence at 3 eV, which is excited at 9 and 28 eV and T = 295 K, includes a fast component (<1 ns) along with a slow component (34 ms). The position of the maximum E em = 3.0 eV does not change at temperatures from 5 to 295 K [1]. A new luminescence near 3.3 eV [5] was detected in the cathodic luminescence spectrum, which was measured at T = 77 K with a nanosecond resolution without any time delay relative to the excitation pulse in crystals containing anion vacancies predominantly in the form of F-centers.…”

“…The F-center, which is active in recombination processes in oxygen-deficient α-Al 2 O 3 crystals, has a radiative transition at 295 K in the blue-violet range with a maximum E em = 3.0 eV, the full width at the half maximum FWHM = 0.44 eV and the decay time τ = 34 ms [1]. The absence of polarization or a weak polarization of the optical absorption (OA) of the F-center at 6.05 eV [2,3] and a considerable anisotropy [1,2] of its luminescence at 3 eV confirms the supposition [2], which is based on a long-time decay of the luminescence, about the triplet-singlet origin of the radiative transition.…”

Time-resolved optically stimulated luminescence and spectral emission features of α-Al2O3:C

“…Vinceller et al [46] because the F band is known to show photocurrents down to 10 K [2,47]. The emission at 3.0 eV (420 nm) is generated by the transition from the 3 P excited state to the 1 S ground state [2,4,48].…”