Herein, we report a trap-tuning strategy involving alkali metal ions of Li+ and K+, which enabled a fine tuning of afterglow traps at 250 K. Through Li+/K+ doping, a red afterglow from Cs2AgInCl6:Mn was activated at room temperature, which was extended up to 3600 s at low temperature. Thermoluminescence measurement revealed a shallow trap at ∼0.50 eV below the conduction band, which could be shifted up- and down-ward by dopant species.