Luminescence-based gas indicators, which detect gases by monitoring luminescence modulation, have attracted increasing interest due to advancement in technologies of LED and detectors. These indicators provide intuitive visual confirmation of gas presence. In this study, we focused on Eu3+-doped Bi2MoO6 (BMO:Eu) nanophosphors for the luminescent-based gas detection of hydrogen sulfide (H2S). BMO:Eu nanophosphors were synthesized using a hydrothermal method to achieve nanoscale morphology, which enhances gas adsorption capacity through an increased surface area. The synthesized BMO:Eu exhibited characteristic red luminescence originating from Eu3+ ions. Upon exposure to 500 ppm of H2S, the red luminescence intensity decreased by approximately 42%, and the extent of quenching showed clear dependence on the H2S concentration (10–500 ppm), indicating that BMO:Eu can quantitatively detect H2S. X-ray diffraction patterns revealed lattice expansion after exposure to H2S, while diffuse reflectance spectra showed a reduction in reflectance in the visible range. Density functional theory calculations indicated that reduced reflectance was due primarily to the reduction of Bi3+ and Mo6+ in BMO:Eu, rather than oxygen substitution by sulfur. X-ray photoelectron spectroscopy confirmed the presence of Bi2+ and Mo5+ species, elucidating that the observed luminescence quenching was due to these reduction processes. Moreover, in situ photoluminescence lifetime measurements showed a decrease in lifetime from 0.76 (before exposure) to 0.62 ms (after exposure), demonstrating that quenching occurred via the formation of nonradiative recombination centers.
