Recently emerged metal halide perovskites have been widely recognized as a promising class of semiconductor materials for next-generation optoelectronic devices, owing to their useful photonic and electronic properties. [1][2][3] Particularly, Lead-free 0D metal halide perovskites are emerging environmentally friendly materials exhibiting large exciton binding energy, which have recently attracted great attention for their excellent light emission properties and favorable stability. Herein, solvent evaporation crystallization at room temperature is adopted to fabricate 0D Cs 3 Cu 2 I 5 perovskite millimeter-sized crystals, which show strong blue photoluminescence (PL) with quantum yield of up to 89%, a large Stockes shift and long (microsecond) PL lifetime, originating from selftrapped excitons. UV pumped light-emitting diodes are demonstrated by using Cs 3 Cu 2 I 5 powder as a solid-state phosphor, and the precursor solution of these perovskite crystals is used as a fluorescent ink. Furthermore, blue-emitting composite Cs 3 Cu 2 I 5 /polyvinylidene fluoride films are produced by spin coating through the solvent evaporation and followed patterning using a direct laser writing technology, which are potentially useful for displays. Finally, the solvent evaporation crystallization method is expanded to fabricate yellow emissive CsCu 2 I 3 crystals by changing the chemical molar ratio of precursor.

X-ray imaging, [17][18][19] and light-emitting diodes (LEDs) due to their remarkable optoelectronic properties. [20][21][22][23][24][25][26] However, the lead toxicity and instability are serious issues toward their commercialization, [27,28] promoting the exploration of lead-free perovskite derivatives in the past several years. [29,30] One straightforward approach to replace Pb 2+ is to employ isovalent substitution of Sn 2+ and Ge 2+ owing to the same electronic configuration of ns 2 np 0 . [31] Regrettably, due to the high-energy-lying Sn 2+ 5s 2 and Ge 2+ 4s 2 states, Sn 2+ and Ge 2+ can be easily oxidized into Sn 4+ and Ge 4+ in ambient atmosphere, resulting in dominant defects of halogen vacancies and interstitial metals. [32][33][34] Another strategy to alleviate the toxicity of Pb 2+ is to adopt monovalent B + cations and trivalent B 3+ cations to form double perovskites with a general chemical formula of A 2 B + B 3+ X 6 , [35][36][37] such as Cs 2 AgBiX 6 , Cs 2 AgInX 6 , and Cs 2 AgSbX 6 , which suffer from low emission efficiencies ascribed to indirect bandgaps or direct forbidden bandgaps. [28,[38][39][40] Recently, vacancy-ordered perovskites have emerged as promising candidate for substitution of lead halide perovskites, owing to their advantages of high stability and high defect tolerance. The crystal unit of vacancy-ordered perovskites is very similar to that of the double perovskites, formed by doubling the conventional perovskite ABX 3 unit cell along all three crystallographic axes, subsequently removing every other B site cations. [41][42][43][44] Some efforts have been made to fabricate vacancy-ordered double perovskites in the past few years. For example, solvent-thermal method was adopted to fabricate Cs 2 ZrCl 6 (need 180 °C for 10 h), [31] and Cs 2 ZrX 6 (X = Cl, Br) nanocrystals were also got by using strict air-free Schlenk line technique. [45] Cs 2 TeI 6 film was fabricated by employing antisolvent method under a nitrogen atmosphere with controlled levels of H 2 O (<5 ppm). [46] Cs 2 SnI 6 nanocrystals were synthesized via hot-injection process at high temperature of 220 °C. [47] Obviously, challenges still lay ahead in terms of developing facile and low cost strategies under mild conditions to explore novel vacancy-ordered double perovskites.The grinding approach based on mechanochemistry as one of green and emerging efficient synthetic method which was Lead-free vacancy-ordered double perovskites with formula of A 2 M(IV)X 6 have become promising alternatives to lead halide perovskites. Herein, novel direct bandgap lead-free vacancy-ordered double perovskites Rb 2 ZrCl 6−x Br x (0 ≤ x ≤ 2) with highest photoluminescence quantum yield (PLQY) of 90% are synthesized by using a facile wet grinding approach. Experimental and theoretical analyses demonstrate that the bright emissions originate from the self-trapped excitons (STEs). Additionally, thermally activated delayed fluorescence (TADF) is observed in these perovskites, confirmed by temperature-dependent steadystate PL spectra and ...

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Polarized emissive materials with anisotropic nanostructures have attracted tremendous attention as potential substitutes for polarizers. Herein, the electrospinning technique is adopted to realize in situ fabrication of lead-free halide Cs 3 Cu 2 I 5 nanostructures embedded in poly(vinylidene fluoride) (PVDF) micro/ nanofiber films for polarized luminescence generation, with a photoluminescence quantum yield (PLQY) of 33.3−86.1%. The functionality of the polymer PVDF as a protector and its interactions with Cs 3 Cu 2 I 5 were demonstrated. The Cs 3 Cu 2 I 5 /PVDF composite nanofibers exhibit a higher degree of PL polarization ratio (P) than that of composite microfibers, reaching a highest P of 0.4 and long-term stability. This polarized emission is attributed to the directional transition dipole moment (TDM) induced by the asymmetric crystal structure of aligned Cs 3 Cu 2 I 5 nanorods and dielectric confinement effect of the PVDF matrix. The universality of the in situ electrospinning preparation strategy is confirmed by the fabrication of a Cs 3 Cu 2 I 5 /PVA fiber film with a P of 0.5. The reported Cs 3 Cu 2 I 5 /polymer nanofiber films with bright and highly polarized light emissions will have great potential for optoelectronic applications such as liquid crystal display (LCD) backlighting, spectrum splitting, waveguides, lasers, and polarized photodetectors.

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