The photoluminescence (PL) spectra and PL excitation spectra (PLES) of microcrystalline powders of CaGa2S4:5%Tm,5%Yb and CaGa2S4:5%Tm thiogallates were studied at room temperature. The PLES were measured in the wavelength range from 240 to 850 nm, and the PL spectra were measured in the range of 400–2100 nm with excitation in the UV and violet-blue spectral regions. Microcrystalline gadolinium oxychloride powder GdOCl:5%Tm, in which thulium ions are in the trivalent state (Tm3+), was used as a sample for comparison of properties. It was concluded that thiogallates contain thulium ions in both di- and trivalent states (Tm2+ and Tm3+). In this case, the absorption of excitation energy by the CaGa2S4:5%Tm crystal is ensured primarily by the 4f–5d transition of the Tm2+ ion, while in the CaGa2S4:5%Tm,5%Yb compound, it is additionally due to the formation of charge transfer states from CaGa2S4 ligand atoms to Yb3+ ions. It was shown that in CaGa2S4:5%Tm crystals co-activated with Yb3+ ions, the photoluminescence efficiency increases many times over compared to non-co-activated crystals, and the effective excitation range extends to 530 nm.