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 CsCu ₂I ₃ MCs, rather than Cs ₃Cu ₂I ₅ MCs, preferred to be formed. However, when the anti-solvents with polarity came to lower than 4.3 ^-, particle-state Cs ₃Cu ₂I ₅ MCs would be produced. With the structural evolution from CsCu ₂I ₃ to Cs ₃Cu ₂I ₅ , 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 CsCu ₂I ₃ and Cs ₃Cu ₂I ₅ 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 CsCu ₂I ₃ and Cs ₃Cu ₂I ₅ MCs in next-generation solid-state lighting.