Realizing Multicolor and Stepwise Photochromism for On-Demand Information Encryption

This work achieves dual-mode light- and heat-responsive step-by-step coloration via trap engineering in the Ba 5 (PO 4 ) 3 Cl:Eu 2+,Ce 3+,F – (BPCF) phosphor. A three-step calcination (BPCF-III) strategy promotes the redistribution of multitraps and balances three color-centers to facilitate photoinduced electron transfer processes. The BPCF-III shows controllable color tunability due to the distinct energy stimulation for each color-center with different trap depths. The powder color changes from white to red after 254 nm irradiation at RT, then turns to yellow upon optical stimulation at 532 nm or heating at 150 °C and to green upon 200–300 °C heating, and finally recovers to white upon 450 or 405 nm stimulation or heating above 350 °C. The powder color can also vary to green directly when T = 200–300 °C, where the charging wavelength extends from 254 to 405 nm. Such multicolor and stepwise photochromism in a single matrix presents a significant guideline for designing high-performance photochromic material-based devices.