Anti-solvent polarity engineering for structure, morphology and composition control of cesium copper (I) halide with efficient, stable and adjustable photoluminescence

In this work, cesium copper (I) halide micro-crystals (MCs) were demonstrated to experience structure, morphology and composition evolutions by tuning the polarity of the anti-solvent. It was fond that, when anti-solvents with the polarity higher than 4.3+ were used, rod-like phase-pure CsCu2I3 MCs, rather than Cs3Cu2I5 MCs, preferred to be formed. However, when the anti-solvents with polarity came to lower than 4.3-, particle-state Cs3Cu2I5 MCs would be produced. With the structural evolution from CsCu2I3 to Cs3Cu2I5, the photoluminescence emission changed from yellow to blue, with high photoluminescence quantum yields (PLQYs) of 15.3% and 89.5%, respectively. Amazingly, by a fine tuning of the polarity in the range from 4.3+ to 4.3-, the mixing ratio of CsCu2I3 and Cs3Cu2I5 MCs can be adjusted directly, with tunable Commission Internationale de L′Eclairage (CIE) color coordinates from cold white to white and warm white, by changing the relative volume of the anti-solvent. Note that, the dependences of the production on the polarity of the anti-solvent showed rather wide precursor’s molar ratio and concentration processing windows. At last, the as-prepared white-light mixture was placed onto a UV LED chip to fabricate a white-light emitting diode (WLED). The device showed a high color rendering index of 87.3, a CIE color coordinate of (0.32, 0.33), and a long life time of more than 100 h. The discovered relationships between the anti-solvent polarity and structural evolution of the cesium copper (I) halide MCs enriched our understanding about copper-containing perovskite-like halides. The method to fabricated white-light phosphor in one step greatly simplified the technological process and reduced the production cost. And, the perfect stability of the WLED demonstrated promising application prospect of CsCu2I3 and Cs3Cu2I5 MCs in next-generation solid-state lighting.