Full-Color upconversion luminescence nanoplatform for real three-dimensional volumetric color displays

Real three-dimensional (3D) volumetric display, as a pursuable ultimate goal in the field of display, have attracted extensive interest in both fundamental research and various frontier applications. In particular, the emergence of solid-state 3D display technology based on upconversion processes offers a versatile and powerful tool to achieve truly spatial naked-eye 3D displays. However, the realization of a solid-state real 3D volumetric color display with high spatiotemporal resolution in upconversion nanoparticles (UCNPs) at a single nanoparticle level remains a great challenge. Herein, without multiple compositions of UCNPs and high excitation power density or complex pulse excitation modulation, a specifically well-designed nanostructures of multilayer core–shell UCNPs, by manipulating energy transfer pathways, enables us to realize excitation power density-independent orthogonal red–green–blue (RGB) emissions with high color purity by utilizing near-infrared multiwavelength excitations. Notably, full-color emissions, involving red, orange, yellow, green, blue, indigo, violet, and white upconversion luminescence, can be dynamically regulated in this multilayer architecture by adjusting excitation wavelength and power density of the combined 980/808/1560 nm lasers. These emission profiles of multilayer UCNPs make them promising for a wide range of applications. As a proof of concept, we demonstrated their potential for application in real 3D volumetric full-color display. By incorporating such UCNPs into epoxy resin AB glue to construct transparent display matrices, the naked-eye-based 3D volumetric color display images with high color pixel and optical resolution can be achieved by moving the focal point of the laser beams within the stereo display matrices. These findings will benefit the future development of convenient and versatile optical technique for the fine tuning of full-color luminescence in a single nanoparticle level, and provide the possibility to construct true 3D volumetric full-color display technologies with high brightness, nanometer range display resolution, and multi-perspective display.