Novel Two‐Step Topotactic Transformation Synthetic Route Towards Monodisperse LnOF:Re,³⁺ (Ln = Y, Pr–Lu) Nanocrystals with Down/Upconversion Luminescence Properties

Abstract

functional nanodevices require meticulous mastery over the size and morphology of the materials at the nanometer scale. [ 3 ] Therefore, the synthetic strategy for nanocrystals has long been a central and fundamental theme in the nanoscience and nanotechnology. The current synthetic innovations for nanocrystals tend to emphasize the green concept being confronted with global energy and environmental crisis. [ 4 ] During the last decades, tremendous effort has been invested in the synthesis of inorganic nanocrystals by various synthetic routes. The notable examples include monodisperse noble metals, [ 5 ] metal oxides, [ 6 ] and semiconductors with closed shapes (e.g., cube, octahedron) and hierarchical architectures (e.g., fl ower-like). [ 7 ] The mainly practical synthetic routes are solution-based cothermolysis of metal complex precursors and solvothermal method. [ 8 ] However, these synthetic routes usually need harsh conditions, including toxic organometallic precursors, and hazardous coordinating solvents, which have been matters of environmental concern. Besides, the stringent control over series of experimental variables and tedious processes for separation and purifi cation further restricts their availability and utility. [ 9 ] Therefore, it is of great academic interest and practical signifi cance to seek facile and green synthetic strategies for nanomaterials.Lanthanide (Ln) luminescence has played an irreplaceable role in the forefront of science and technology due to the fascinating optical properties originating from the intra 4f transitions, including narrow emission band, large Stockes shift or anti-Stockes shift, and long-lived luminescence. [ 10 ] Choosing an appropriate host matrix is the precondition for Ln 3+ optical transitions. Among them, lanthanide oxyfl uorides have been considered to be attractive candidates for host materials, because they possess the low phonon energy of the lanthanide fl uorides counterparts, the good chemical durability, thermal stability, and excellent mechanical strength of the oxides counterparts. [ 11 ] Moreover, it is expected that the presence of oxygen may widen the excitation range and enhance the emission intensity through the O 2− →Ln 3 + charge transfer (CT). [ 12 ] To date, several

Microwave-Assisted Solvothermal Synthesis of Upconverting and Downshifting Rare-Earth-Doped LiYF4 Microparticles

“…Interestingly, further increase in the Li + to RE 3+ ratio to 7.5 resulted in the formation of yttrium hydroxy fluoride nanorods (Figure A3) and LiF (Figure B3). The XRD pattern of the obtained nanorods is in good agreement with those reported for numerous Y­(OH) x F y systems with varying OH to F ratios. − Their chemical composition and approximate weight fraction in the sample were determined to be Y­(OH) 0.75 F 2.25 and 73%, respectively, via Rietveld refinement. The reader is referred to Figures S4 and S5 and Table S2 in the Supporting Information for details.…”

Monodisperse NaxY(OH)yF3+x–y Mesocrystals with Tunable Morphology and Chemical Composition: pH-Mediated Ion-Exchange

“…On the basis of the previous report on the thermal gravity (TG) curves of this type compound, the typical thermal decomposition temperature is around 350−500 °C, and this decomposition releases H 2 O molecules. 22,23,29,31,33 Novel micro-/nano-REdoped LnOF luminescent materials can be effectively obtained via this further thermal decomposition. 22,23 As a controllable and reversible reaction, this topochemical ion-exchange route is complex.…”

“…22,23,29,31,33 Novel micro-/nano-REdoped LnOF luminescent materials can be effectively obtained via this further thermal decomposition. 22,23 As a controllable and reversible reaction, this topochemical ion-exchange route is complex. The XRD patterns indicate that the structures of β-NaYF 4 (JCPDS No.…”

“…27 Very recently, lanthanide oxyfluorides with special nano-/microstructures also can be prepared by topotactic transformation from different precursors. 15,18,22,23,25 Experimental variables have a profound influence on morphology, size, and composition of the final samples. 15,28,29 When other experimental parameters remain, the morphological evolution and chemical composition changing of the Y(OH) x F 3−x and NaY(OH) x F 4−x exhibit a dependence on the changing of the OH − amount or pH values.…”

The pH-dependent reactions in the sonochemical synthesis of luminescent fluorides: The quest for the formation of KY3F10 crystal phases

“…Be that as it may, it is important to note that, to the best of our knowledge, this is the first publication in which an ultrasound-assisted process is described for the fabrication of yttrium hydroxyfluorides. Particularly, these materials can be used as precursors to produce the greatly appreciated YOF compounds by topotactic transformations or thermal decompositions [40] , [41] .…”