A systematic theoretical and experimental study was carried out to find a relationship between photoluminescence emissions and photocatalytic activity of Ag2SeO4 obtained by different synthesis methods (sonochemistry, ultrasonic probe, coprecipitation and microwave assisted hydrothermal synthesis). Experimental characterization techniques (XRD with Rietveld refinement, Raman, FTIR, UV-vis, XPS and photoluminescence spectroscopy) were used to elucidate its structural order at short, medium, and long ranges. Morphological analysis performed by FE-SEM showed distinct morphologies due to the different methods of synthesis. Based on density functional theory (DFT) calculations, it was possible to study in detail the Ag2SeO4 surface properties, including its surface energy, geometry, and electronic structure for the (100), (010), (001), (101), (011), (110), (111), (021), (012) and (121) surfaces. The equilibrium morphology of Ag2SeO4 was predicted as a truncated octahedron with exposed (111), (001), (010) and (011) surfaces. Photoluminescence emissions showed a band covering the visible spectrum, and the Ag2SeO4 obtained by the coprecipitation method presented the most intense band with a maximum in the red region. Photocatalytic results confirmed that Ag2SeO4 synthesized by the sonochemistry method is the best photocatalyst for rhodamine B degradation under UV light irradiation.