A novel topotactic transformation route towards monodispersed YOF:Ln3+ (Ln = Eu, Tb, Yb/Er, Yb/Tm) microcrystals with multicolor emissions

Abstract

Design and synthesis of inorganic micro/nanocrystals with target phase/morphology is a focal theme in nanoscience and nanotechnology. Herein, a novel in situ topotactic transformation synthesis strategy, Y₄O(OH)₉NO₃ → Y(OH)_2.02F_0.98 → YOF towards YOF:Ln³⁺ (Ln = Eu, Tb, Yb/Er, Yb/Tm) microcrystals has been reported. We have elaborated the in situ topotactic transformation from Y₄O(OH)₉NO₃ to Y(OH)_2.02F_0.98 based on the topotactic structural matching, where similar anisotropic channel structures along the c-axis and the analogous coordination structure of lanthanide ions were involved. We have also extended this synthesis strategy to the topologically isomorphic Y(OH)₃ and β-NaYF₄ and found that the fine difference in structural evolution during the transformation processes led to different morphological evolutions for the two. To the best of our knowledge, for the first time, we report such an in situ topotactic transformation with a high degree of crystal lattice rearrangement, where enneagonal channels transformed into hexagonal channels while maintaining the morphology contour. Moreover, we have systematically investigated the influences of experimental variables on the morphology, size, and composition of the final products. Furthermore, the luminescence properties of the as-prepared YOF:Ln³⁺ microcrystals were emphasized by demonstrating the multicolor emissions via downconversion and upconversion luminescence. Our study may provide significant guidance towards the synthesis of inorganic micro/nanocrystals with a target phase structure/morphology on the basis of topotactic structural matching.