Growth and reversible discoloration of KCuCl₃ and K₂CuCl₄·2H₂O crystals

In this work, KCuCl₃ and K₂CuCl₄·2H₂O crystals were synthesized via a solution evaporation method. Their crystal structures were verified by XRD, while the (110) interplanar spacing of K₂CuCl₄·2H₂O was further identified by HRTEM and the corresponding SAED. Thermal behavior was examined using TG/DSC. Both compounds exhibit reversible discoloration in response to temperature (20–100 °C) and humidity (0–80 % RH). UV–Vis absorption reveals band gaps of 3.05 eV for KCuCl₃ and 3.09 eV for K₂CuCl₄·2H₂O. PL spectra show blue-green emission, with CIE coordinates indicating a warmer hue for K₂CuCl₄·2H₂O, primarily attributed to the Cu 2+ centers. The strong light absorption and efficient PL response of these halides highlight their potential for humidity sensing and luminescent device applications.