Facile hydrothermal crystallization of NaLn(WO4)2 (Ln=La-Lu, and Y), phase/morphology evolution, and photoluminescence

Hydrothermal reaction of Ln nitrate and Na2WO4 at pH=8 and 200 degrees C for 24 hours, in the absence of any additive, has directly produced the scheelite-type sodium lanthanide tungstate of NaLn(WO4)(2) for the larger Ln(3+) of Ln=La-Dy (including Y, Group I) and an unknown compound that can be transformed into NaLn(WO4)(2) by calcination at the low temperature of 600 degrees C for the smaller Ln(3+) of Ln= Ho-Lu (Group II). With the successful synthesis of NaLn(WO4)(2) for the full spectrum of Ln, the effects of lanthanide contraction on the structural features, crystal morphology, and IR responses of the compounds were clarified. The temperature-and timecourse phase/morphology evolutions and the phase conversion upon calcination were thoroughly studied for the Group I and Group II compounds with Ln=La and Lu for example, respectively. Unknown intermediates were characterized by elemental analysis, IR absorption, thermogravimetry, and differential scanning calorimetry to better understand their chemical composition and coordination. The photoluminescence properties of NaEu(WO4)(2) and NaTb(WO4)(2), including excitation, emission, fluorescence decay, and quantum efficiency of luminescence, were also comparatively studied for the as-synthesized and calcination products.