Water-induced crystal phase transformation of stable lead-free Cu-based perovskite nanocrystals prepared by one-pot method

[Display omitted] •Highly stable Cs3Cu2X5 (X = Cl, Br, I) NCs with near-unity PLQY (X = Cl and I) were prepared by a facile one-pot method.•Crystal phase transformation was observed in water post-treatment of Cs3Cu2I5 NCs and a plausible mechanism was proposed.•W-LED constructed by mixing Cs3Cu2I5 and CsCu2I3 possessed CIE coordinates of (0.32, 0.34). Cu-based perovskite Nanocrystals (NCs) have a bright future in the field of optoelectronics due to their low toxicity, remarkable optical properties and good environmental stability. However, the industrial application is hindered by complex preparation methods. Herein, a facile one-pot method for synthesizing Cs3Cu2X5 NCs is proposed. The target Cu-based perovskite NCs were qualified with preferable optical performance, including near-unity PLQY (X = Cl and I), adjustable spectrum from 441 to 556 nm and remarkable environmental stability (retained more than 50% Photoluminescence (PL) intensity for 2 months in air). Density functional theory (DFT) calculations, Time-resolved PL (TRPL) and temperature-dependent PL spectrum were implemented to explore the Self-trapped excitons (STEs) luminescence mechanism and the roots for remarkable optical performance. In addition, crystal phase transformation was observed in water post-treatment from blue light-emitting Cs3Cu2I5 NCs to yellow light-emitting CsCu2I3 NCs, relative characterizations were implemented and a plausible reaction mechanism was proposed. Resultantly, a White light-emitting diode (W-LED) constructed by mixing these two phases was endowed with pure white light, which possessed the Commission Internationale de L'Eclairage (CIE) coordinate of (0.32, 0.34), color temperature of 6053 K, color Rendering index (Ra) 0f 91 and maximum luminance of 1558 cd/m2. The contribution indicates that Cu-based perovskite NCs prepared by one-pot method have great potential for luminescent applications.