Glycothermal Synthesis of Scheelite-Type LiEuW₂O₈ Nanophosphors and Their Structural Characterization

Abstract

The formation of LiEuW 2 O 8 from a tungsten source and acetates of lithium and europium(III) by autoclave treatment in 1,4butylene glycol, i.e., by a glycothermal reaction, was studied to explore a novel low-temperature wet chemical synthesis of scheelite-type tungstate compounds with WO 4 units. When dodecatungstophosphoric acid hexahydrate (DPA) was chosen as a tungsten source, a glycothermal reaction at 300 C produced crystalline scheelite-type LiEuW 2 O 8 (LEW) nanophosphors in a single phase. In contrast, phase-pure crystalline LEW was not obtained using the other tungsten sources. According to the results obtained by inductively coupled plasma atomic emission spectroscopy, infrared absorption spectroscopy, and Raman spectroscopy, the DPA-derived sample contained PO 4 groups, which had probably substitutionally replaced WO 4 . PO 4 groups could play a significant role in the nucleation of scheelite-type LEW, which is composed of WO 4 groups. We also discuss the nonstoichiometric structural properties of the crystalline scheelite-type LEW. LEW nanophosphors, which are an alternative for organic dyes, may be one of promising materials because of their optical function of color conversion from near UV and blue to red.

Glycothermal Synthesis and Characterization of Scheelite-Type NaEuW[sub 2]O[sub 8] Nanophosphors

“…27,28 For sample DPA-2h200, the additional peak was observed in the region of 1000-1150 cm −1 , which is assigned to the vibrational modes of PO 4 units. These PO 4 units originate from the starting ingredient, DPA, 20 and the results agree with that of XRF analysis. Other peaks are assigned to alkyl chain and carboxyl groups, which are derived from the starting glycol solvents and the metal acetates.…”

“…This would result in the acceleration of the formation of crystalline NEW. 20 Formation of crystalline scheelite-type NEW nanophosphor with the aid of phosphate groups.-Most of the diffraction peaks of sample APT-2h300P ͑Fig. 1d͒ prepared using the additional phosphorus additive, ADP, were mainly assigned as NEW.…”

“…This is in contrast to scheelite-type LEW nanophosphors, where the secondary phase appears 1 day after preparation, as already mentioned in the Introduction. 20 To investigate the change in the extent of the crystalline phase, the integral intensity of the XRD ͑112͒ peak of scheelite-type NEW relative to that of MgO, I scheelite /I MgO , and the full width at half-maximum ͑fwhm͒ value of the ͑112͒ peak were calculated ͑Table II͒. The estimated values did not show any appreciable change during keeping at room temperature for 5 months.…”

“…19 Furthermore, we reported that the scheelite-type LEW crystal can be synthesized by the glycothermal method. 20 We pointed out that the PO 4 units derived from a tungsten source dodecatungstophosphoric acid hexahydrate ͑DPA͒ are possibly substitutionally incorporated into LEW to promote the crystallization of LEW. On the other hand, the obtained sample has the following problems: ͑i͒ When the as-prepared sample was kept at room temperature, the secondary phase with a pseudoscheelite or wolframite structure crystallizes from the amorphous phase in the sample, 21 ͑ii͒ adsorption of organic species such as glycol molecules hardly occurs, and ͑iii͒ coalescence of primary particles occurred to form necks.…”

Synthesis and luminescence properties of Yb3+ and Er3+ doped KLa(WO4)2 nanoparticles

“…But in recent years, it has been revealed that the materials with grain size less than 100 nm exhibited different properties from conventional microcrystalline specimens [4][5][6][7]. Many kinds of luminescent materials have been prepared in nanocrystalline state by various methods [8][9][10].…”