Fluorophosphate Upconversion-Luminescent Glass-Ceramics Containing Ba₂LaF₇:Er³⁺ Nanocrystals: An Advanced Solid-State Nuclear Magnetic Resonance Study

Abstract

Fluorophosphate glass-ceramics containing Ba2LaF7:Er3+ nanocrystal upconversion-luminescent materials were prepared via a melt-quenching method, followed by heat treatment. The glass structure evolution, which was induced by the change in composition, as well as heat treatment, was characterized via solid-state nuclear magnetic resonance (SSNMR) spectroscopy. Multiple Q n mLa phosphorous species (n and m represent the numbers of P–O–P and P–O–La bonds, respectively) were proved via multiple 31P magic-angle spinning (MAS). Three fluorine species [P–F···Na, Ba–F···Na, and (Ba, La)–F···Na] were resolved using 19F MAS spectra. Unlike Y3+, La3+ cannot attract F to form an La–F···Na linkage in phosphate glasses. Furthermore, dissimilar to the competition behavior between the positive ions to attract F–, the 19F NMR results demonstrates that Ba2+ and La3+ combined preferentially to attract F–, thus inducing the preferential formation of the (Ba, La)–F···Na species, followed by the ultimate precipitation of the Ba2LaF7 crystal after the heat treatment. The paramagnetic effects of Er3+ on 19F and 31P indicates that there are still many Er3+ ions in the glass phase after crystallization, even though the Er3+ ions dominated the Ba2LaF7 crystal. The evolution of the 31P spectrum via crystallization indicates that the precipitation of Ba2LaF7 facilitates the polymerization of the phosphorus glass network. Finally, a structural evolution model is developed.

Bright Transparent Scintillators with High Fraction BaCl2: Eu2+ Nanocrystals Precipitation: An Ionic‐Covalent Hybrid Network Strategy toward Superior X‐Ray Imaging Glass‐Ceramics

“…To validate our research strategy, a series of fluorochloroaluminate-phosphate (FCAP) glasses and glass ceramics with the molar composition of (44-x)AlF 3 -36(CaF 2 -SrF 2 -YF 3 )-(20-y)BaF 2 -xAl(PO 3 ) 3 -yBaCl 2 (x = 0, 3, 5, 7, 9, 11; y = 0, 5, 10, 15, 20; x ] polyhedral chain. [25] The 27 Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra further reveal that the environment of Al 3+ ions is six-coordinated predominantly, with a small amount of five-coordination (Figure S2a, Supporting Information). [26] Raman spectra (Figure 1a) and 31 P MAS NMR spectra (Figure S2b, Supporting Information) further indicate that the Q n phosphorous species (n represents the number of P-O-P bond) in G 5P is mainly Q 1 species, and the Q 2 species is increased with the content of Al(PO 3 ) 3 .…”

“…[26] Raman spectra (Figure 1a) and 31 P MAS NMR spectra (Figure S2b, Supporting Information) further indicate that the Q n phosphorous species (n represents the number of P-O-P bond) in G 5P is mainly Q 1 species, and the Q 2 species is increased with the content of Al(PO 3 ) 3 . [27] The introduced Q 1 and Q 2 species can reduce the ionic characteristic of glass network and improve the glass forming ability. Characteristic temperatures including glass transition temperature T g , the first onset crystallization temperature T x1 and melting temperature T m were determined from differential scanning calorimetry (DSC) curves to obtain the T g /T m and T x1 -T g as the indicators of the glass forming ability [28] (GFA) during the melt-quenching process and the glass stability [29] (GS) during the heating process respectively (Figure 1b; Table S1, Supporting Information).…”

“…[34] The 31 P MAS NMR spectra of the G 15Cl and GC 15Cl show that the Q 2 content increased after BaCl 2 nanocrystallization (Figure S2b, Supporting Information), suggesting that the glass network was repolymerized and strengthened. [27] As an extra benefit, an appropriate BaCl 2 molar fraction (up to 15 mol.%) included in the FCAP glass can also improve the GS due to the mixed-anion effect (Figure S9, Supporting Information). [35] All the GCs with different BaCl 2 content maintain high transparency (Figure S10, Supporting Information).…”

“…Solid-state NMR experiments were carried out on a Bruker Avance III HD 500 M spectrometer (11.7 T). The resonance frequencies were 130.4, 202.6, 470.8, and 49.1 MHz for 27 Al, 31 P, 19 F and 35 Cl, respectively. All the spectra were recorded using a 4-mm Bruker magic angle spinning (MAS) probe.…”

“…All the spectra were recorded using a 4-mm Bruker magic angle spinning (MAS) probe. 27 Al MAS spectra were obtained at a spinning speed of 12 kHz. The pulse length is 0.73 μs (10°liquid angle) with a recycle delay of 0.5 s. 31 P MAS spectra were obtained at a spinning speed of 12 kHz.…”