Template-free hydrothermal synthesis and luminescence properties of NaGd(WO 4 ) 2 :Eu 3+ red phosphors with controlled morphology

A series of morphology-controlled NaGd(WO4)2:Eu3+ phosphors were prepared by a facile hydrothermal method in the absence of any surfactants and templates. X-ray diffraction, scanning electron microscopy and photoluminescence spectra were used to characterize the obtained products. It was found that the pH value of the precursor solution had a remarkable impact on the phase structure, morphology and luminescent properties of the products. The possible formation mechanism for square plate structure was proposed based on the time-dependent experiments. Moreover, the effects of the initial pH value, reaction time and Eu3+ concentration on the luminescent properties of NaGd(WO4)2:Eu3+ phosphors were investigated in detail. The results revealed that the square plate-like microcrystals synthesized at pH = 8 for 20 h showed excellent red emission under near-ultraviolet (NUV) excitation. In addition, no concentration quenching occurred when the Eu3+ concentration was as high as 0.6. The intense red emission and high red color purity showed that NaGd(WO4)2:Eu3+ microplates had promising applications as red component in NUV-excited WLEDs.