Multicolor Fine‐Tunable Upconversion Luminescence from a Single Nanoparticle for Full‐Color Displays with a Wide Color Gamut

Abstract Recently, upconversion nanophosphor (UCNP)‐based displays have received increased attention, with emerging reports on transparent displays utilizing multicolor upconversion luminescence from single UCNPs. For these display devices, color reproducibility is one of the most essential properties and the multicolor‐emitting UCNPs are required to exhibit a wide color gamut (WCG) for enhanced color reproducibility. However, achieving both high brightness and WCG properties simultaneously remains challenging for multicolor‐emitting single UCNPs. Here, bright red/green/blue (RGB) orthogonal luminescent core@sextuple‐shell (C@6S) UCNPs showing a WCG under 800, 980, and 1532 nm near‐infrared (NIR) light is reported. Luminescent properties of various C@6S UCNPs with 6 distinct R‐G‐B configurations are investigated and a green‐emitting core coated with a red‐emitting inner shell and a blue‐emitting outer shell satisfied high brightness and WCG properties. The green‐emitting core‐based C@6S UCNPs showed multicolor tunability with high brightness and the widest color gamut value of 94.2% of the National Television System Committee color space among RGB‐emitting core@multishell UCNPs. Furthermore, potential full‐color displays utilizing the transparent C@6S UCNP‐polydimethylsiloxane composite and NIR light sources are demonstrated. These findings provide the criteria for synthesizing the RGB‐emitting single UCNPs exhibiting high brightness and a WCG and would be beneficial for the realization of true 3D full‐color displays.