Zinc gallate (ZnGa₂O₄) spinel ceramics doped with Mn²⁺ ions was prepared by a solid-state reaction at 1200 °C in air. Manganese concentration was equal to 0.05 mol.% of MnO with respect to ZnO. Ceramics produced in this way show an efficient green emission at about 505 nm under UV or X-ray excitations, which is caused by Mn²⁺ ions. This green emission is observed also as a relatively long afterglow (visible to the naked eye in the dark for about one hour) after switching-off the X-ray excitation. Time profiles of the beginning of glow and afterglow have been studied together with thermally stimulated (TSL) and optically stimulated (OSL) luminescence. Experimental results demonstrate a presence of few types of shallow and deep traps responsible for the observed afterglow and TSL/OSL emission of the material. The possibility of pulsed optical stimulation and time-resolved OSL characteristics of ZnGa₂O₄: Mn²⁺ has been reported for the first time. The presented results suggest the ZnGa₂O₄: Mn²⁺ spinel as a promising material for further fundamental research and possibility of application as a green long-lasting phosphor or storage phosphor for TSL/OSL radiation dosimetry.

Detailed investigations of the spectroscopic properties of Cr ³⁺ ions in β-Ga ₂ O ₃ :0.05% Cr ³⁺ single crystals grown by the floating zone technique have been performed in the temperature range 4.5–550 K. The luminescence of Cr ³⁺ ions at low temperatures is due to narrow R-lines ( ² E → ⁴ A ₂ transitions) and their vibronic sidebands, whereas the broad intense band ( ⁴ T ₂ → ⁴ A ₂ transition) dominates at temperatures above 200 K. The vibronic sidebands of R-lines with amplitude of less than 5% of the R ₁ -line at a temperature of 4.5 K cover the region of 700–735 nm. The temperature dependences of the luminescence intensity and the decay time of Cr ³⁺ ions indicate the same mechanism of quenching of R-line intensity and shortening of lifetime for ² E of Cr ³⁺ ions. The temperature dependence of the R ₁ -line decay time of β-Ga ₂ O ₃ :Cr ³⁺ with maximal temperature coefficient |Δτ/Δ T | = 0.023 ms K ⁻¹ at 120 K and maximal specific sensivitity |(Δτ/Δ T )τ ⁻¹ | = 0.017 K ⁻¹ at 160 K indicates an application potential of this phosphor for low-temperature fluorescence thermometry.

We suggest a method for optimizing geometry of acousto-optic (AO) interactions in anisotropic crystalline materials. Within the framework of this method, one gets global maximums of AO figure of merit M₂ and their spatial orientations, proceeding from so-called “extreme” indicative surfaces, which are obtained after finding such an acoustic wave propagation direction that maximizes the M₂ parameter for each propagation direction of the incident electromagnetic wave. The method improves earlier indicative surface-based techniques in several aspects, particularly in properly accounting for the momentum conservation condition for the AO diffraction, and yields a higher accuracy in assessing spatial anisotropy of the AO effect. We have constructed the extreme surfaces of LiNbO₃ crystals for all possible cases, including those of isotropic/anisotropic AO diffractions and longitudinal/transverse acoustic waves. The anisotropy of the AO figure of merit for LiNbO₃ is analyzed for the acoustic frequencies 0.01–2.0 GHz and the light wavelengths 405–1444 nm. The absolute M₂ maximums refer to ‘indirect crystal cuts' and are equal to 26.3 × 10⁻¹⁵ s³/kg at 2 GHz and 405 nm, and 15.4 × 10⁻¹⁵ s³/kg at 0.4 GHz and 1444 nm.