Tunable Warm to Cool White Light Emission from La-Doped and Na-Alloyed Cs₂AgInCl₆ Double Perovskites for Efficient Light-Emitting Diode Applications

All-inorganic double perovskites (DPs) are gaining huge attention due to their excellent optoelectronic properties. Both doping and alloying of foreign substances have been considered as efficient approaches to tailor the electronic and optical properties of perovskite materials. Herein, we report the tunable white light emission by doping of La in the alkali metal (Na)-alloyed Cs2AgInCl6 double perovskite (DP) prepared by a facile solvothermal method. The obtained samples were highly stable and showed enhanced photoluminescence (PL) compared to the pristine Cs2AgInCl6. Importantly, the Na-alloying and La-doping approach relaxed the parity-forbidden transition and improved exciton binding energy, thereby providing a large stoke shift, which was identified from broadening of the PL spectrum with full width at half-maximum (FWHM) > 183 nm and a prolonged emission decay of >340 ns studied by time-correlated single-photon counting (TCSPC) measurements for La (0.5 and 1%)-doped DP (Cs2Ag0.5Na0.5InCl6) samples. In addition, the synthesized samples were coated on UV-LED to demonstrate the commercial application for white light-emitting diodes (WLEDs). Further, the color gamut of all of the fabricated WLEDs was observed using a spectrophotometer equipped with an integrating sphere. Na-alloyed DP (Cs2Ag0.5Na0.5InCl6) samples showed warm white light emission with a correlated color temperature (CCT) of 4189 K and a color rendering index (CRI) of 86.63. However, the minimal doping of La3+ (0.5%) ions in the DP host (Cs2Ag0.5Na0.5InCl6) effectively tuned the white light emission from warm to cool white light emission (CCT, 5010 K; CRI, 90.09). Na-alloying combined with La-doping on Cs2AgInCl6 DP would be a promising strategy for all-inorganic tunable white light emission for backlight LED applications.