Tunable and Stable White Light Emission in Bi³⁺-Alloyed Cs₂AgInCl₆ Double Perovskite Nanocrystals

Lead-free double perovskite nanocrystals (NCs) of Cs₂AgIn_1–xBi_xCl₆ (x = 0, 0.05, 0.15, 0.3, 0.6, and 1) were synthesized with control over the size distribution. Detailed structural studies were carried out on the resulting double perovskite NCs to confirm the alloying and structural modification. Alloying of Bi leads to change in optical properties, such as the band gap, and enhancement in oscillator strength of first excitonic transition and the white light emission (WLE) properties. The band gap of the double perovskite NCs was estimated; a direct band gap transition value of ∼3.46 eV is obtained for pure Cs₂AgInCl₆ NCs. This value of the band gap has reduced with increase of Bi doping, which also leads a band gap transition from direct to indirect band gap. This system exhibits a sub-band gap emission between ∼570 and 620 nm along with band-edge emission, which is strongly dependent on the alloying concentration. A gamut of emission is observed in the alloyed systems. The Commission International de I’Eclairage (CIE) coordinates of (0.36, 0.35) for the 30% Bi-doped sample, with color rendering index values of ∼91, and correlated color temperature of 4443 with D_uv of −0.0065 are observed, which are found to be very promising for WLE applications.