Inexpensive and highly efficient luminescent materials based on multinary halides have received increased attention in recent years. Among those considered most promising are the perovskites such as CsPbX3 because of their highly efficient and tunable emission through precise control of chemical composition and nanostructuring. However, the presence of the toxic heavy metal Pb and relatively poor stability are among the major challenges for the introduction of lead-halide-based materials into the marketplace. Here, we report the optical properties of nontoxic and highly emissive one-dimensional (1D) all-inorganic halides CsCu2X3 (X = Cl, Br, I) and their mixed halide derivatives, which also show improved thermal and air stability. Photoluminescence (PL) measurements show tunable bright room temperature emission from green to yellow with photoluminescence quantum yields ranging from 0.37 (CsCu2Cl1.5Br1.5) to 48.0% (CsCu2Cl3). Temperature- and power-dependent PL measurements suggest that the emission results from self-trapped excitons induced by strong charge localization and structural distortions within the lD ribbon structure.

The United States Department of Energy (DOE) projects an estimated energy cost savings of $630 billion from 2015 to 2035 if reliable solid-state lighting technologies can be developed and DOE goals are met. [1] For the cost-effective implementation of light-emitting diodes (LEDs), development of new inexpensive light emitters is an urgent need. Owing to their outstanding photophysical properties including tunable bandgaps and emission colors, high photoluminescent quantum yields (PLQY) and excellent color purity, metal halide perovskite LEDs (PeLEDs)

Recently, copper­(I) halides have been gaining increased attention as highly luminescent nontoxic alternatives to lead halide perovskites for optoelectronic applications. Here, we report preparation of blue emitting, lead free, all-inorganic halides K2CuX3 (X = Cl, Br) through five synthetic methods including traditional solid-state and solution methods. The photoluminescence (PL) emission spectra of K2CuCl3 and K2CuBr3 exhibit narrow peaks centered at 392 and 388 nm with full widths at half-maximum (fwhm) values of ∼54 nm. The visible bright blue emission is corroborated by the remarkably high photoluminescence quantum yield (PLQY) values up to ∼97%. Furthermore, radioluminescence measurements on K2CuCl3 yield a bright peak at 404 nm under irradiation with X-rays at 200 kVp and 20 mA, which is optimal for use with PMTs and Si photomultipliers, suggesting a strong potential of this family for radiation detection applications. Based on our combined experimental and computational investigations, the origin of the efficient luminescence in K2CuX3 is attributed to the high stability self-trapped excitons (STE) formed in the one-dimensional anionic ∞ 1[CuX3]2– chains. Advantageously, K2CuX3 demonstrate improved air- and photostability compared to the previously reported copper­(I) halides. The discovery of highly efficient and high stability light emitters based on earth-abundant copper­(I) halides paves the way for their potential practical applications.

Low-dimensional hybrid organic–inorganic metal halides have received increased attention because of their outstanding optical and electronic properties. However, the most studied hybrid compounds contain lead and have long-term stability issues, which must be addressed for their use in practical applications. Here, we report a new zero-dimensional hybrid organic–inorganic halide, RInBr4, featuring photoemissive trimethyl­(4-stilbenyl)­methylammonium (R+) cations and nonemissive InBr4 – tetrahedral anions. The crystal structure of RInBr4 is composed of alternating layers of inorganic anions and organic cations along the crystallographic a axis. The resultant hybrid demonstrates bright-blue emission with Commission Internationale de l’Eclairage color coordinates of (0.19, 0.20) and a high photoluminescence quantum yield (PLQY) of 16.36% at room temperature, a 2-fold increase compared to the PLQY of 8.15% measured for the precursor organic salt RBr. On the basis of our optical spectroscopy and computational work, the organic component is responsible for the observed blue emission of the hybrid material. In addition to the enhanced light emission efficiency, the novel hybrid indium bromide demonstrates significantly improved environmental stability. These findings may pave the way for the consideration of hybrid organic In­(III) halides for light emission applications.

Lead-free halide light-emitting diodes (LEDs) are fabricated using nontoxic and earth-abundant CsCu2I3 with a strong yellow emission at a peak wavelength of 568 nm. CsCu2I3-based host–dopant emitters are formed by vacuum thermal evaporation (VTE) film codeposition process instead of the commonly used solution-based film deposition process. Using the VTE process, extremely thin (30 nm) host–dopant emitters have successfully been formed with the CsCu2I3 dopant and various organic host molecules. A bright yellow emission with a photoluminescence quantum yield value of 84.8% is achieved in the 0.5% CsCu2I3-doped halide emitter film due to the successful spatial localization of charge carriers and excitons using an organic host with appropriate energy levels to CsCu2I3. With the further enhancement in charge balance using the cohost system, a record-breaking lead-free halide LED has been fabricated with an EQE of 7.4%. The lead-free halide LEDs are also highly stable in the device operation with LT70 of 20 h at 100 cd/m2.

Copper(I) halides are emerging as attractive alternatives to lead halide perovskites for optical and electronic applications. However, blue-emitting all-inorganic copper(I) halides suffer from poor stability and lack of tunability of their photoluminescence (PL) properties. Here, the preparation of silver(I) halides A 2 AgX 3 (A = Rb, Cs; X = Cl, Br, I) through solid-state synthesis is reported. In contrast to the Cu(I) analogs, A 2 AgX 3 are broad-band emitters sensitive to A and X site substitutions. First-principle calculations show that defect-bound excitons are responsible for the observed main PL peaks in Rb 2 AgX 3 and that self-trapped excitons (STEs) contribute to a minor PL peak in Rb 2 AgBr 3 . This is in sharp contrast to Rb 2 CuX 3 , in which the PL is dominated by the emission by STEs. Moreover, the replacement of Cu(I) with Ag(I) in A 2 AgX 3 significantly improves photostability and stability in the air under ambient conditions, which enables their consideration for practical applications. Thus, luminescent inks based on A 2 AgX 3 are prepared and successfully used in anti-counterfeiting applications. The excellent light emission properties, significantly improved stability, simple preparation method, and tunable light emission properties demonstrated by A 2 AgX 3 suggest that silver(I) halides may be attractive alternatives to toxic lead halide perovskites and unstable copper(I) halides for optical applications.

Recently, ternary copper­(I) halides have emerged as alternatives to lead halide perovskites for light emission applications. Despite their high-efficiency photoluminescence (PL) properties, most copper­(I) halides are blue emitters with unusually poor tunability of their PL properties. Here, we report the impact of substitution of copper with silver in the high-efficiency blue-emitting Cu­(I) halides through hydrothermal synthesis and characterization of (NH4)2AgX3 (X = Br, I). (NH4)2AgX3 are found to exhibit contrasting light emission properties compared to the blue-emitting Cu­(I) analogues. Thus, (NH4)2AgBr3 and (NH4)2AgI3 exhibit broadband whitish light emission at room temperature with PL maxima at 394 and 534 nm and full width at half-maximum values of 142 and 114 nm, respectively. Based on our combined experimental and computational results, the broadband emission in (NH4)2AgX3 is attributed to the presence of high-stability self-trapped excitons and defect-bound excitons. (NH4)2AgBr3 and (NH4)2AgI3 both have significantly improved air and moisture stability as compared to the related copper­(I) halides, which are prone to degradation via oxidation. Our results suggest that silver halides should be considered alongside their copper analogues for high-efficiency light emission applications.

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