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

Abstract

Lead-free double perovskite nanocrystals (NCs) of Cs2AgIn1–x Bi x Cl6 (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.

Lead‐Free Halide Double Perovskites: Structure, Luminescence, and Applications

“…The variation of lattice parameters as a function of Bi doping tallied with the theoretical Vegard's law line well, indicating an uniform cation distribution. [ 104 ] The volume of the Cs 2 AgIn 1‐ x Bi x Cl 6 unit cell expands from 1151 to 1250 Å 3 when Bi 3+ totally substitutes In 3+ . The linear increase between lattice parameters and substitution concentrations indicates solid‐solution behavior with dopants randomly distributed at B sites.…”

“…(c) Reproduced with permission. [ 104 ] Copyright 2020, American Chemical Society. (d,e) Reproduced with permission.…”

Synthesis of TlBr and Tl2AgBr3 Nanocrystals

“…Bulk TlBr also has a parity‐forbidden indirect transition at 2.6–2.7 eV, but there is no evidence of this feature in the absorbance spectra of the nanocrystals. For the the Tl 2 AgBr 3 nanocrystals, an extrapolation of the linear region of the Kubelka Munk function in Figure B reveals an indirect bandgap of 3.1 eV . There is also an Urbach tail extending to longer wavelength, which could indicate the presence of silver‐thallium antisite defects.…”

Rare Earth‐Free Luminescent Materials for WLEDs: Recent Progress and Perspectives

“…Manna et al showed that Cs 2 AgIn 0.833 Bi 0.167 Cl 6 had a high PLQY of up to 39%, which provided an important reference for the study of the luminescence mechanism of these materials. [ 96 ]…”

“…Manna et al showed that Cs 2 AgIn 0.833 Bi 0.167 Cl 6 had a high PLQY of up to 39%, which provided an important reference for the study of the luminescence mechanism of these materials. [96] Another effective strategy for the construction of lead-free perovskite materials is through the use of low-toxic elements such as antimony (Sb), tin (Sn), and bismuth (Bi) as lead substitutes. [97] In 2018, Tan et al prepared a Bi-doped lead-free inorganic perovskite Cs 2 SnCl 6 :Bi with high-efficiency blue light emission at 455 nm, and a quantum yield close to 80%.…”