abstract
The hexagonal-phase (beta) of NaREF4 upconversion nanocrystals (RE = rare earth elements) has been widely employed because of the outstanding luminescence performance, yet less is known about the essence of this superior property. The current understanding of this issue is raised from the advantage of weak electron-vibration interactions in fluoride systems, while the interpretability of this statement is controversial and contradictory results are commonly reported. One feasible way to solve this puzzle is from the aspect of structure-property relationship, yet even after decades of investigation, the structural details of beta-NaREF4 are still under debate. Herein, the reported results relevant to this topic are reviewed, and the conflicting viewpoints are summarized. The similarities and differences between different lattice templates are assessed, and the reasons underlying the divergence are analysed. Based on these discussions, it is realized that the crystal structure of beta-NaREF4 should be more reliably depicted as one flexible lattice framework with complex characteristics, and the structural disorder induced by atom displacements in the lattice is probably the key to supporting the superior luminescence properties of beta-NaREF4 nanocrystals.
keywords
RARE-EARTH FLUORIDE; ANION-EXCESS FLUORITES; SITU ION-EXCHANGE; LUMINESCENCE PROPERTIES; DEFECT AGGREGATION; ENERGY MIGRATION; SINGLE-CRYSTAL; QUANTUM YIELD; NALNF(4) LN; SIZE
subject category
Chemistry, Multidisciplinary; Nanoscience & Nanotechnology; Materials Science, Multidisciplinary; Physics, Applied
authors
Shi, R; Brites, CDS; Carlos, LD
our authors
Projects
CICECO - Aveiro Institute of Materials (UIDB/50011/2020)
acknowledgements
This work was developed within the scope of the projects CICECO-Aveiro Institute of Materials (UIDB/50011/2020 and UIDP/50011/2020) and NanoHeatControl, POCI-01-0145-FEDER-031469, financed through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement.