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In KTaO3:Er crystals, we observed a temperature shift, unusual for rare earth impurities, for narrow zero-phonon luminescence lines, due to the 4S3/2 → 4I13/2, 4F9/2 → 4I15/2, and 4S3/2 → 4I15/2 transitions in Er3+ impurity ions. The magnitude of the shifts turned out to be comparable with the large shifts of the R lines of the Cr3+ luminescence in SrTiO3:Cr and KTaO3:Cr crystals, that is, substantially larger than that for the three-charged rare earth ions usually observed in the f–f luminescence spectra in ionic crystals.

The f–f absorption and emission spectra of Er3+ impurities were observed and identified in KTaO3 and K1 – xLixTaO3 single crystals. It was shown that Li off-centers related random fields markedly influence intensity, width and position of zero-phonon lines. The detail analysis of the absorption spectra obtained allowed one to determine energies of the Stark sublevels of excited states for Er3+ dominant centers of noncubic symmetry.

Photoluminescence (PL) spectra of Cr doped BaxSr 1 − x TiO 3 (x = 0–0.84) (BST) thin films were investigated for the first time. XRD patterns revealed typical peaks of BST microcrystalline perovskite phase. Chromium doping of BST thin films was accompanied by the appearance of PL consisting of rather pronounced lines centered at 1.570–1.600 eV (789.8–774.9 nm) at 12 K, for x = 0–0.84, respectively. These lines are attributed to the zero-phonon transitions 2 E → 4 A 2 of octahedral coordinated Cr 3+ ions in Ti sites of BST. At T ≥ 165 K, the intra ion d-d transitions in Cr 3 + are not significantly influenced by the neighborhood of CrO 6 complexes.

The emission and excitation spectra of luminescence of Sn2P2S6 crystals were studied within wide temperature (12–360 K) and spectral (260–1200 nm) regions. Analysis of the photoluminescence emission spectra revealed five overlapping bands of nearly Gaussian shape peaking near 1.98, 1.72, 1.48, 1.28, and 1.02 eV at 12 K. Annealing of the orange tinted crystal in vacuum at 300°C for 30 minutes caused a substantial increase of photoluminescence intensity in comparison to the as-grown crystal and their brown coloration. The origin of photoluminescence of the Sn2P2S6 crystals was connected with sulfur vacancies.

The emission and excitation spectra of luminescence of a Sn2P2S6 crystal were studied in detail within wide temperature (12–360 K) and spectral (260–1000 nm) regions. Illumination with monochromatic light with the wavelength shorter than about 710 nm at low temperatures enabled to observe broad-band photoluminescence in the red and near-infrared spectral regions. Analysis of the emission spectra revealed a superimposition of three overlapping bands of nearly Gaussian shape peaking near 1.75, 1.57, and 1.39 eV at 12 K. At steady-state excitation at 12 K, the changes of photoluminescence intensity were observed with time of crystal illumination. During subsequent heating of the crystal with a rate of 0.082 K/s weak thermoluminescence was observed within 15–130 K. The trap depths of 41 and 88 meV, corresponding to two pronounced glow peaks near 22 and 41 K, were determined by the “initial rise” method.

In Hg 2 Cl 2 crystals broad luminescence bands excited with UV light have been studied in the spectral range 0.8–2.25 eV. The measurements have been performed on as-grown crystals and on crystals previously exposed to UV light at RT. The emission spectra consist of six bands peaking at 0.82, 1.06, 1.23, 1.39, 1.51, and 1.72 eV with FWHM of 0.21–0.33 eV. Their intensities depend conspicuously on the concentration of the photochemical products induced by irradiation of the crystals at RT. It is concluded that the infra-red luminescence of Hg 2 Cl 2 originates from crystal defects, especially that complexes (HgCl x Br 3− x ) − and (HgCl x Br 4− x ) 2− are responsible for these emissions. Excitation of the luminescence can occur: (i) via excitons in the Hg 2 Cl 2 matrix, (ii) via excited states of Hg 2 Br 2 molecules, and (iii) resonantly through the excitation bands of defect centres. A configurational coordinate diagram for the emission observed at 1.51 eV is proposed. A model for the temperature quenching of luminescence and energy transfer between two different kinds of centres is used to explain the more complicated temperature dependence of this luminescence.

The dielectric permittivity and photoluminescence of the title films were studied in detail. SrTiO3:Cr films show a temperature maximum of e′ (T) and a saturation of the TO-mode softening near 100 K. In (SrCa)TiO3:Cr films a temperature maximum of e′ occurs at 28 K; we suggest this is due to an onset of XY, n = 2 quantum ferroelectricity. A ‘blue shift’ of the zerophonon R-luminescence line of octahedral Cr3+ in SrTiO3 films, and an increase of vibronic sideband intensities in comparison with Cr3+ luminescence in the same crystals are reported and discussed. Attention was focussed on SrTiO3:Cr films in order to explain a large and unusual temperature shift of the R-luminescence line position. It is shown that this shift is a consequence of local configurational instability and the off-center position of Cr3+ in the ground 4A2-state and the excited 2E-state, which occurs at least for T < 77 K.