E Key Laboratory of Oral and Maxillofacial Development and Regeneration, Wuhan 430022, China Correspondence: [email protected] (C.H.); [email protected] (Q.S.)Citation: Wang, M.; Wei, H.; Wang, S.; Hu, C.; Su, Q. Dye Sensitization for Ultraviolet Upconversion Enhancement. Nanomaterials 2021, 11, 3114. https://doi.org/10.3390/ nano11113114 Academic Editors: Marcin Runowski and Julia P ez-Prieto Received: 20 October 2021 Accepted: 11 November 2021 Published: 18 NovemberAbstract: Upconversion nanocrystals that converted near-infrared radiation into emission within the ultraviolet spectral region supply lots of exciting opportunities for drug release, photocatalysis, photodynamic therapy, and solid-state lasing. On the other hand, a key challenge is the development of lanthanidedoped nanocrystals with efficient ultraviolet emission, as a result of low conversion efficiency. Here, we create a dye-sensitized, heterogeneous core ultishelled lanthanide nanoparticle for ultraviolet upconversion enhancement. We systematically study the main influencing things on ultraviolet upconversion emission, which includes dye concentration, excitation wavelength, and dye-sensitizer distance. Interestingly, our experimental outcomes demonstrate a largely promoted multiphoton upconversion. The underlying mechanism and detailed energy transfer pathway are illustrated. These findings present insights into future developments of extremely ultraviolet-emissive nanohybrids and supply far more possibilities for applications in photo-catalysis, biomedicine, and environmental science. Key phrases: lanthanide nanoparticles; ultraviolet upconversion; dye sensitization; heterogeneous nanoparticles; energy transfer; luminescence enhancement1. Introduction Lanthanide-doped upconversion nanoparticles can absorb near-infrared (NIR) laser light and emit visible and ultraviolet light, with prospective applications in bioimaging [1], biotherapy [62], and so on. In unique, the applications of these nanoparticles in optogenetic [13,14], photothermal [15,16], and photodynamic [179] therapy may be accomplished by way of ultraviolet (UV) light emission beneath NIR excitation. Though UV light is usually obtained by Nd3 – and Yb3 -sensitized upconversion [17,18,20,21], it’s difficult to realize the high luminescence intensity JPH203 manufacturer needed to