Facile Melting-Crystallization Synthesis of Cs₂Na_xAg_1–xInCl₆: Bi Double Perovskites for White Light-Emitting Diodes

Abstract

Lead-free double perovskites (DPs) have outstanding luminescent properties, which make them excellent candidates for wide use in optoelectronics. Herein, a solvent-free melting-crystallization technique, which can produce kilogramscale DP microcrystals (DP-MCs) in one batch, is invented to synthesize the Cs 2 Na x Ag 1−x InCl 6 : Bi (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) DP-MCs. The structure and composition analysis confirmed the products are pure Cs 2 Na x Ag 1−x InCl 6 DP-MCs. Affected by Jahn− Teller distortion of AgCl 6 octahedra, self-trapped excitons appear in the excited state, resulting in the broadband emission (400−850 nm) of Cs 2 Ag 1−x Na x InCl 6 : Bi DP-MCs. The enhancement of the photoluminescence quantum yield can be realized by introducing Na + to break the parity-forbidden transition in the Cs 2 AgInCl 6 DP. Optimized Cs 2 Na 0.4 Ag 0.6 InCl 6 : Bi DP-MC phosphors combined with commercial blue and green phosphors were coated on ultraviolet chips (365 nm) to fabricate white light-emitting diodes (WLEDs) from warm white (2930 K) to cold white (6957 K). An ultrahigh color rendering index of 97.1 and a CCT of 5548 K as well as Commission Internationale de l'Eclairage color coordinates of (0.331, 0.339) have been demonstrated. This kilogram-scale synthesis technique could stimulate the industrial development of WLEDs for general lighting based on DP-MC phosphors.

Self-trapped excitons in soft semiconductors

“…This phenomenon was attributed to the thermal expansion of the lattice and the electron–phonon renormalization, which have been widely observed in various STE-related materials. 38,61,62…”

“…In low-dimensional perovskite, molecular substitution, coordination number adjusting, and metal cation substitution are also widely used for tuning the STE properties. 27,62,63,142–149 Smith et al studied the STE emission of a series of 2D Pb–Br hybrid perovskites, which were fabricated by adjusting the organic cation. 63 Broadband STEs emissions were commonly observed in 9 different types of Pb–Br perovskites, and the relative intensities of the STEs emission spectra were correlated with the increasing out-of-plane distortion and organic cations.…”

Metal halide perovskites-based white light-emitting diodes

“…The composite films exhibit (e) Normalized PL emission spectra of Cs2NaxAg 1−x InCl6: Bi microcrystals (insets are the images of microcrystals). Reprinted with permission from [75]. Copyright (2022) American Chemical Society.…”

“…Furthermore, WLEDs was prepared by uniformly coating the mixture of the efficient dual-color emitting Mn 2+ doped (PEA) 2 PbBr 4 NCs, CsPb(Cl/Br) 3 NCs (495 nm emission), and PMMA/toluene on UV-LED chips (405 nm) (figure 2(f)). In lead-free perovskite systems, Zhang et al implemented a melting-crystallization strategy without solvent to prepare kilogram-scale Bi 3+ -doped Cs 2 Na x Ag 1−x InCl 6 microcrystals [75], which show a white light broadband emission (400-850 nm) and a high PL efficiency (figure 2(e)). By coating perovskites combined with commercial blue and green phosphors (figure 2(d)), they fabricated WLED with a high CRI of 97.1 and Commission Internationale de l'Eclairage (CIE) color coordinates of (0.331, 0.339).…”

Improving the luminescence property of the novel yellow-emitting phosphor SrLa2Sc2O7:Bi3+ with charge compensators (Li+, Na+, K+) and its application in NUV-based white LEDs

“…However, the emission peaks of rare earth doped phosphors are generally narrow, with the FWHM usually in the range of 20-100 nm, and therefore a high color rendering index (CRI) cannot be achieved. 6 Therefore, the subject of phosphor materials with a wide emission range in the visible region has drawn considerable attention. Bi has the electronic configuration of [Xe]4f 14 5d 10 6s 2 6p 3 , and its naked 6s and 6p electrons are not protected from external electrons and are therefore very sensitive to changes in the surrounding local crystal field, 7,8 to an extent that in some substrates it has the potential to function as an activator for a wide range of emissions.…”