Phase-Transition-Driven Regional Distribution of Rare-Earth Ions for Multiplexed Upconversion Emissions
Zeyu Lyu, Hao Dong, X. C. Yang, Ling Huang, Yuejiao Xu, Ke Wu, Ling‐Dong Sun, Chun‐Hua Yan
Abstract
High Resolution Image Download MS PowerPoint Slide Phase transition of the polymorphs is critical for controlled synthesis and property modulation of functional materials. Upconversion emissions from an efficient hexagonal sodium rare-earth (RE) fluoride compound, β-NaREF 4, which is generally obtained from the phase transition of the cubic (α-) phase counterpart, are attractive for photonic applications. However, the investigation of the α → β phase transition of NaREF 4 and its effect on the composition and architecture is still preliminary. Herein, we investigated the phase transition with two kinds of α-NaREF 4 particles. Instead of a uniform composition, the β-NaREF 4 microcrystals exhibited regionally distributed RE 3+ ions, in which the RE 3+ with a smaller ionic radius (smaller RE 3+ ) sandwiched the RE 3+ with a larger ionic radius (larger RE 3+ ). We unravel that the α-NaREF 4 particles transformed to β-NaREF 4 nuclei with no controversial dissolution, and the α → β phase transition toward NaREF 4 microcrystals included nucleation and growth steps. The component-dependent phase transition is corroborated with RE 3+ ions from Ho 3+ to Lu 3+ and multiple sandwiched microcrystals were obtained, in which up to five kinds of RE components were distributed regionally. Moreover, with rational integration of luminescent RE 3+ ions, a single particle with multiplexed upconversion emissions in wavelength and lifetime domains is demonstrated, which provides a unique platform for optical multiplexing applications.