Cs2AgInCl6 lead-free double perovskites are environmentally benign with easily modulated fluorescence. However, their wide band gap (∼3.3 eV) and forbidden optical transitions limit their visible application. Herein, we prepared Cs2AgInCl6 microcrystals (MCs) and corresponding doped samples (bismuth: Bi3+, samarium: Sm3+, and Bi3+–Sm3+) to achieve such a functionality by a precipitation method at low temperature (80 °C). Bi3+-doped Cs2AgInCl6 MCs introduce 1S0 to 1P1 absorption with a fluorescence enhancement at lower excitation energy (370 nm). Although the f–f transition of Sm3+ is parity forbidden, Bi3+–Sm3+ co-doped Cs2AgInCl6 MCs show a combination of luminescence in the visible range with two sharp additional spectral features at 567 and 600 nm, which are attributed to the 4G5/2 → 6H5/2 (∼567 nm) and 4G5/2 → 6H7/2 (∼600 nm) transitions of Sm3+ ions. We proposed a mechanism in which Cs2AgInCl6:Bi–Sm MCs achieve mutual enhancement of fluorescence through recombination of self-trapped excitons and energy-transfer transitions. Moreover, thermogravimetric (TG) analysis indicated that the materials have remarkable thermal stability. Afterwards, light-emitting diodes (LEDs) with bright yellow light were fabricated by combining Cs2AgInCl6:Bi–Sm MCs with a 365 nm chip, and the corresponding color coordinate is about (0.535, 0.440) with a 2000 K correlated color temperature (CCT). [ABSTRACT FROM AUTHOR]