Monodisperse Na_xY(OH)_yF_3+x–y Mesocrystals with Tunable Morphology and Chemical Composition: pH-Mediated Ion-Exchange

Abstract

This work reports self-assembled uniform monodisperse Na x Y­(OH) y F3+x–y (0 < x < 1, 0 < y < 3) mesocrystals with tunable morphology and chemical composition obtained from a hydrothermal ion-exchange reaction. Detailed crystal structure analysis illustrates that the special crystal structure of Na x Y­(OH) y F3+x–y (0 < x < 1, 0 < y < 3) facilitates the pH-mediated ion-exchange process. A possible topochemical-based mechanism has been proposed to this ion-exchange process. By carefully adjusting the pH value of the solution, the tunable three-dimensional (3D) Na x Y­(OH) y F3+x–y (0 < x < 1, 0 < y < 3) mesocrystal architectures are obtained through an oriented self-assembly. The photoluminescence properties of the rare earth ions (such as Eu3+, Tb3+, and Ce3+) doped as-prepared mesocrystal samples are investigated, and multicolor emissions are realized.

Remarkably Enhanced Red Upconversion Emission in β-NaLuF4:Er,Tm Microcrystals via Ion Exchange

“…First, the main diffraction peak shifts toward larger angles and the cell volume decreases with respect to the ion exchange reaction. Second, the space between (110) and (101) diffraction peaks decreased from 1.077° to 0.998°, probably due to the substitution of small F – ions (1.285 Å) for large OH – ions (1.32 Å) in agreement with the previous reports (Figure c–e) …”

“…This energy migration facilitates excitation energy diffusion within the sensitizer sublattice and energy transfer to the emitters and boosts the upconversion emission. If NH 4 HF 2 is used alone during post-treatment, a relatively small increase (2.26 times enhancement) in the upconversion intensity is observed probably due to a collaborative effect of the substitution of F – ions for OH – ions and Na + ions trapped into the hexagonal tunnels, according to previous reports (Figure c). , Indeed, after the ion exchange, the ratio of Na + to RE 3+ increases from 0.905 to 0.926, also meaning that the decrease in the OH – concentration is in accordance with the above results (Table S1). It is well known that the ion exchange reaction depends strongly on the concentration of Na + and F – ions in the reaction mixture.…”

“…Because of the identical electronic structure and chemical similarity, OH – in the hydrophilic reactants is likely incorporated into the host lattices by substituting F – ions. ,, OH – defects have been shown to be a serious quencher for the upconversion emission of Er 3+ . − The 4 I 11/2 to 4 I 13/2 energy gap (3500 cm –1 ) is resonant with the high-energy OH – vibrations (∼3500 cm –1 ), and the 4 I 11/2 excited state could easily be quenched via one-phonon process. Also, the quenching of the 4 I 13/2 excited state occurs through a two-phonon relaxation process because the energy gap of the 4 I 13/2 → 4 I 15/2 ground state is 6600 cm –1 .…”

“…Second, the space between (110) and ( 101) diffraction peaks decreased from 1.077°to 0.998°, probably due to the substitution of small F − ions (1.285 Å) for large OH − ions (1.32 Å) in agreement with the previous reports (Figure 1c− e). 51 With the substitution of F − ions for OH − ions, the revolution of the coordination environment of rare-earth ions will cause a possible change of coordination symmetry, checked by investigating the luminescence properties variations of Eu 3+ -doped β-NaLuF 4 crystals. 57,58 The electric-dipole transition emission of 5 D 0 → 7 F 2 is strongly local structuredependent, while the magnetic-dipole transition of 5 D 0 → 7 F 1 is inert to its surrounding.…”

A Polyol-Mediated Fluoride Ions Slow-Releasing Strategy for the Phase-Controlled Synthesis of Photofunctional Mesocrystals

“…Mesocrystals are three-dimensional (3D) order nanoparticles superstructures with unique properties and various potential applications as functional materials [35,36,37,38]. Nevertheless, the range of known mesocrystallines remains quite limited, in which few investigations to fluorine-containing compound mesocrystallines are available [39,40,41,42,43,44,45]. More recently, our group fabricated yttrium hydroxide fluoride mesocrystalline, as well as its Eu 3+ doped analogue, by means of an additive-free hydrothermal procedure, which involved the reaction of Y(NO 3 ) 3 , NaF, and NaOH aqueous solution without any organic additives [39].…”