<p>The photoluminescence (PL) spectra and PL excitation (PLE) spectra of microcrystalline powders of two thiogallates, CaGa₂S₄:5%Tm,5%Yb and CaGa₂S₄:5%Tm, were studied at room temperature. The PLE spectra were measured in the wavelength range from 240 to 850 nm and the PL spectra were measured in the range 400–2100 nm with excitation in the UV and violet-blue spectral regions. Microcrystalline gadolinium oxychloride powder GaOCl:5%Tm, containing thulium ions in the trivalent state (Tm³⁺) was used as a sample for the comparison of properties. These thiogallates were found to contain thulium ions in both di- and trivalent states (Tm²⁺ and Tm³⁺). The absorption of excitation energy by the CaGa₂S₄:5%Tm crystal is attributed predominantly to the 4f–5d transition of the Tm²⁺ ion, while in CaGa₂S₄:5%Tm,5%Yb, the absorption is also attributed to the formation of charge transfer states with transfer from CaGa₂S₄ ligand atoms to Yb³⁺ ions. The photoluminescence efficiency in CaGa₂S₄:5%Tm crystals coactivated by Yb³⁺ ions was found to be many times greater than in the non-coactivated crystals, while the effective excitation range extends to 530 nm.</p>