Cs₂NaBiCl₆ double perovskite with indirect band demonstrates near-infrared (NIR) wide-band emission, but its low efficacy limits its potential applications in the field of NIR. In this work, micron-sized Cs₂Ag_0.1Na_0.9BiCl₆:Tm³⁺ double perovskites were synthesized via the coprecipitation method, which shows enhanced NIR emission. Their optical absorption, photoluminescence emission (PL) and excitation (PLE), time-resolved photoluminescence, and photoluminescence quantum yield (PLQY) were investigated. The Cs₂Ag_0.1Na_0.9BiCl₆:Tm³⁺ shows optical bandgap of 3.06 eV and NIR broad emission peaking at 680 nm under 350 nm excitation due to recombination of self-trapped excitons (STEs). Meanwhile, a new emission peak could be observed at 810 nm due to Tm³⁺ doping. The PLQY in the band range of 780-830 nm can be increased by 6.05 times from 1.67% to 11.77% and in the band range of 650-900 nm can reach 25.22%. This study proves the feasibility of Cs₂Ag_0.1Na_0.9BiCl₆:Tm³⁺ double perovskite as new NIR emission material.