Revealing the Structures in Short- and Middle-Order of Lanthanum-Doped Al 2 O 3 –NaPO 3 Glasses by Solid State NMR Spectroscopy

Glasses in the x La 2 O 3 - y Al 2 O 3 -(100 – x – y )NaPO 3 system were synthesized by a melt quenching method, where 0 ≤ x ≤ 7.5, y = 0 and x = 5, 5 ≤ y ≤ 15. The structures were characterized by advanced multinuclei solid-state nuclear magnetic resonance spectroscopy (SSNMR) and X-ray photoelectron spectroscopy (XPS). 31 P MAS NMR spectroscopy indicates that the glass Q 2 structure is depolymerized by La 2 O 3 and Al 2 O 3, forming multiple Q x Al n and Q y La n phosphorus species, where n, x, and y represent the number of P–O–P, P–O–Al, and P–O–La bonds, respectively. The various phosphorus species were identified by the J -coupling effect based one and two-dimensional (1D and 2D) experiments such as 2D J- resolved, 1D refocused INADEQUATE and 1D 31 P{ 27 Al} J -coupling heteronuclear multiple quantum coherence (HMQC). La is used as a mimic to simulate the local structure of the luminescent rare earth ions. 139 La wideband uniform rate smooth truncation quadrupolar Carr–Purcell–Meiboom–Gill (WURST-QCPMG) spectra show that the coordination number of La is dominantly nine, and some La atoms transfer to lower coordination with the addition of Al 2 O 3 . La, Al, and Na atoms exclusively bond to phosphorus tetrahedron PO 4, which is evidenced by the 31 P/ 23 Na, 31 P/ 27 Al double resonance NMR, XPS, and the calculation of charge balance. However, the Al/P and La/P connection methods are much different based on the calculation of charge balance and bond number. Finally, comprehensive and novel local structure models are developed for these rare earth-doped aluminum phosphate glasses.