A cationic substitution strategy was employed to synthesize phosphor K2NaIn1-xAlxF6: Cr3+, Mn4+ with enhanced optical properties and thermal stability

Based on crystal field theory and inspired by advancements in photovoltaic catalysis, a series of luminescent materials, K₂NaIn_0.88-xF₆: 0.1Cr³⁺, 0.02Mn⁴⁺, xAl³⁺ (x = 0.015–0.035), were synthesized via the hydrothermal method. Compared to the K₂NaIn_0.88F₆: 0.1Cr³⁺, 0.02Mn⁴⁺ phosphor, the introduction of Al³⁺ led to a substantial enhancement in luminescence properties: the luminescence intensity increased by 1.73 times, and the quantum yield (QY) rose from 36.8 % to 59.2 %. To uncover the mechanism behind this improvement, first-principles calculations were performed to analyze changes in the band gap and density of states of the K₂NaInF₆ host upon Al³⁺ doping. These studies provided detailed insights into the root cause of the luminescence enhancement following the partial substitution of In³⁺ by Al³⁺. Additionally, the doped samples demonstrated improved resistance to thermal quenching. At 423 K (150 °C), the luminescence intensity retained 80.46 % of its value at room temperature, representing an approximate 5 % increase in thermal stability. This was further supported by calculations of the Debye temperature and activation energy. In conclusion, a device featuring NIR pc-LED was created utilizing the NIR phosphor that was synthesized. When operating at a current of 350 mA, the NIR output power attained 190.58 mW; while at a lower current of 50 mA, the device achieved an electrical conversion efficiency of 15.4 %. Additionally, the material was effectively utilized for biological imaging and night-vision purposes, producing promising results.