Although multiple emissive materials are of great research interest due to their great potential in a variety of applications, it is still challenging to prepare highly luminescent color-tunable phosphors. Herein, the authors report a series of Pb−Sn alloyed single crystals, (CNH)PbSnBr (x = 0 to 1), that are equipped with two independent self-trapped excitons (STEs) emitters. Multicolor luminescent output from blue to red and white light can be obtained by tailoring the composition, excitation wavelength, temperature, or time gating. More importantly, the synergistic effect between PbBr and SnBr enables (CNH)PbSnBr to have an extremely high luminescent efficiency up to near unity and remarkably extends stability in ambient air, significantly outperforming the monometallic (CNH)PbBr and (CNH)SnBr. As an encouraging result of the richly endowed emission property and robust stability, (CNH)PbSnBr is further employed in multifunctional applications including the luminescent radiometric thermometer, white light emitter, and high-security anti-counterfeit materials.