Abstract Thermal quenching (TQ) is the main problem of the current red emitting phosphors, which need to be resolved. Here we report a red emitting phosphor KGdF4:0.20Eu3+,0.06 Tb3+ (KGF:0.20Eu3+,0.06 Tb3+) prepared by hydrothermal method. The phosphor exhibits a high stability, due to a large negative thermal quenching at 25–300 °C, caused by conversion thermal energy into light energy. The results show that the co-doping of Tb3+ not only enhances the emission intensity of Eu3+, but also increases negative thermal quenching. Based on negative thermal quenching, the phosphor can be applied as red emitting phosphor for UV excited WLEDs.