LAUSR

Abstract Exploring NASICON-type materials emerges the fully ordered NaHf2(PO4)3 compound. Its cation/vacancy distribution forms an absolutely structural ordering three-dimensional arrangement. Further preparing a solid solution following Na1+xHf2−xScx(PO4)3:Eu (NHSx:Eu; 0.0 ≤ x ≤ 1.6) confirms all compounds are isostructural. Densely atomic-connected framework guarantees the efficient blue emission, which yields > 90% photoluminescence quantum yield (PLQY) for all scandium-substituted analogues, yet the existence of heavy amount of luminescence killer (Eu3+) limits the performance of NaHf2(PO4)3:Eu as a luminescent phosphor. Moreover, a controllable structural ordering/disordering is achieved by varying x value, which is confirmed by Raman and 31P MAS NMR spectra. The structural ordering/disordering is crucial in determining structural rigidity. Consequently, despite the voids in the framework filled with sodium ions as x increases has positive contribution to the structural robustness, cation/vacancy ordered form still builds the most rigid structure for NHS0.3, as established by the NHS0.3 composition possessing the highest Debye temperature within the scandium-involved analogues, which are extracted experimentally by the low temperature specific heat measurements. As such, NHS0.3:Eu has the best thermal stability across the x range, which keeps 90% of integrated intensity up to 203 ℃ compared with room temperature value. This work provides insight into the structural specialty of NASICON structure.