Synthesis, characterization and luminescence properties of NaY(OH) x F 4-x : Sm with spindle shape

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

“…As shown in Figure b, the increasing of the pH value causes a decreasing of the F/Y (and Na/Y) ratio and an increasing of the O/Y (H/Y) ratio in final samples. The ion-exchange process leads to the substitution of F – by OH – and releasing of Na + ions from the crystal structure. ,− ,− ,− In basic solution, the excessive OH – keeps the substitution of F – by OH – kinetically favorable. In contradiction to the variation trend of O/Y, the variation trends of F/Y and Na/Y are similar.…”

“…With the increasing of the pH value, the increasing of the OH – content leads to the decrease of local coordination space of Na + ions, which is responsible for the decreasing of the Na + content. Thus, this topotactic ion-exchange transformation can be described as follows: with the substitution of F – ions for OH – ions, the inserted Na + ions release from the tunnels in the crystal structure. ,− ,− ,− This ion-exchange leads to the formation of final samples with tunable chemical composition at different pH values. ,− ,− ,− The formula of the as-prepared samples may be defined as Na x Y­(OH) y F 3+x‑y . This topotactic transformation is one reversible process: β-NaYF 4 ↔ Na x Y­(OH) y F 3+ x ‑ y ↔ Y­(OH) 3 .…”

“…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.…”

“…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. 12,18,27−29 Thus, it is eagerly demanded to give a detail discussion on the topochemical ionexchange processes during the hydrothermal processes.…”

“…The topotactic transformation strategy can be used to directly synthesize high quality β-NaYF 4 nano-/micro-/mesocrystals from lanthanide hydroxides [Ln­(OH) 3 ] and lanthanide hydroxide fluoride [Ln­(OH) 3 F 3– x ] precursors by avoiding the intermediate routine cubic-hexagonal (α–β) phase transfer. ,,,,− ,− The reversal transformation process from β-NaYF 4 to Ln­(OH) 3 F 3– x also was reported . Very recently, lanthanide oxyfluorides with special nano-/microstructures also can be prepared by topotactic transformation from different precursors. ,,,, Experimental variables have a profound influence on morphology, size, and composition of the final samples. ,, 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. ,,− Thus, it is eagerly demanded to give a detail discussion on the topochemical ion-exchange processes during the hydrothermal processes.…”