Controlling Red Color–Based Multicolor Upconversion through Selective Photon Blocking

Photon upconversion multiplexing has attracted increasing interest in recent years; however, realizing the red color–based multicolor-tunable output in upconversion nanoparticles (UCNPs) at a fixed composition remains a huge challenge. Here, a novel and versatile approach to fine-control upconversion luminescence (UCL) colors from UCNPs through selectively confining specific excitation energy by the photon blocking effect is reported. Four types of dual-color switchable UCNPs capable of emitting red-blue and red-green emissions are successfully designed following this strategy, and their UCL performance shows a multiwavelength (808/980/1550 nm) excitable feature that is well sustained in a wide range of excitation power density. The use of the photon blocking effect further enables the dynamically switchable red-green-blue UCL with 808/980 nm excitations. These findings provide a general method to achieve multicolor-tunable UCL at a single nanoparticle level. Moreover, the UCNPs with red-based multicolor emissions in this work enriches the upconversion system and should have potential applications in display, anti-counterfeiting, and bioimaging.