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 ⁴G_5/2 → ⁶H_5/2 (∼567 nm) and ⁴G_5/2 → ⁶H_7/2 (∼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).