Self‐Trapped Exciton to Dopant Energy Transfer in Rare Earth Doped Lead‐Free Double Perovskite

Abstract

Low dimensional halide perovskites with self‐trapped excitons (STEs) emission have emerged as promising white light phosphors because of their ultrabroadband emission covering the entire visible spectrum from 400 to 800 nm. Such a broad emission from a single material can overcome emission color change and self‐absorption problems within multiple phosphors. However, the color rendering index (CRI) and correlated color temperature (CCT) as two essential parameters of white light quality can hardly be modulated in these perovskite materials. Here, rare earth ion Ho3+ is introduced into Cs2(Na,Ag)InCl6 for the first time, utilizing the hydrothermal method. Besides the strong warm white STEs emission, the as‐synthesized materials exhibit effective characteristic emission of Ho3+ in the visible region. Further, the mechanism of associated emission is explored and the existence of energy transfer from STEs to rare earth is first confirmed. A white light‐emitting diode (LED) prototype is also fabricated by employing the Ho3+ doped Cs2(Na,Ag)InCl6 as the color conversion material on a commercial 365 nm GaN LED chip, achieving an improved CRI from 70.3 to 75.4 compared to the pure Cs2(Na,Ag)InCl6. This result suggests a promising way to achieve high quality single phase all‐inorganic white phosphors and this mechanism has enormous potentials in other optoelectronic applications.

Multimodal Luminescent Yb3+/Er3+/Bi3+‐Doped Perovskite Single Crystals for X‐ray Detection and Anti‐Counterfeiting

“…Although the RE doped luminescence properties of Cs 2 Ag 1‐ x Na x InCl 6 has been reported in previous works by Tang et al., the upconversion properties are usually not involved. [ 51 ] This is attributed to the different energy transfer mechanism, where the Yb ions are able to directly absorb the excitation energy rather than indirectly absorbing from the host. The luminescence decay curves of RE‐1, RE‐2, and RE‐3 fitted luminescence lifetimes show that RE‐1 has the longest luminescence lifetime up to 2 ms (Figure 2h).…”

Recent Advances and Optoelectronic Applications of Lead‐Free Halide Double Perovskites

“…In terms of the f–f transition, the Yb 3+ ‐doped Cs 2 AgBiX 6 (X=Cl, Br) NCs exhibit a near‐infrared emission at 1000 nm, [83] which is also observed in Cs 2 AgInCl 6 [84] . Moreover, the Ho 3+ ‐doped Cs 2 (Na, Ag)InCl 6 LED devices exhibit dual emission, including warm white emission and the effective characteristic emission of Ho 3+ in the visible region [85] …”

Near‐Unity Cyan‐Green Emitting Lead‐Free All‐Inorganic Cesium Copper Chloride Phosphors for Full‐Spectrum White Light‐Emitting Diodes

“…Recently, low‐dimensional lead‐free metal halide phosphors, such as (Ph 4 P) 2 SbCl 5 , Rb 2 CuX 3 (X = Cl, Br), (C 4 N 2 H 14 I) 4 SnI 6 , and Cs 2 (Ag 0.6 Na 0.4 )InCl 6 , have attracted great attention because they exhibit high PLQY, broadband emission, and large Stokes shift. [ 16–22 ] The luminescence of these phosphors is generally originated from the self‐trapped excitons (STEs). Although the low‐dimensional metal halides, especially those with one‐dimensional (1D) structures, have been proposed as emitters for general lighting, they hardly emit bright cyan‐green color.…”