Surfactant-assisted hydrothermal process, shape-control, and photoluminescence of Eu 3+ -doped lutetium tungstate micros
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Three-dimensional (3D) sphere-like Eu3+-doped white light lutetium tungstate phosphors have been fabricated by the cationic surfactant cetyltrimethyl ammonium bromide (CTAB)-assisted hydrothermal method, which presents a diameter of ;2-lm morphology assembled by nanoflakes with a length of 100 to ;200 nm. The results demonstrate that CTAB, suitable pH values, reaction time, and reaction temperature are all essential for the formation of lutetium tungstate microspheres. Photoluminescence measurement indicates that lutetium tungstate microspheres show a broad O–W Charge transfer state (CTS) transition and the characteristic emission of Eu3+ at ;591 and ;611 nm.
I. INTRODUCTION
The size-controlled and shape-dependent micro- and nanoscale inorganic materials have attracted considerable attention, especially the crystals with ordered superstructures self-assembled by low-dimensional inorganic nanostructure, because of their importance in basic scientific research and potential applications in technology.1–3 Many efforts have been made to explore effective synthetic approaches to the fabrication of a variety of inorganic crystals with complex three-dimensional (3D) nanostructures to enhance their performance in currently existing applications.4–8 Various methods have been used to synthesize 3D microarchitectures, such as the microemulsion method, hydrothermal (solvo-thermal) method, sol-gel method, molten salt method, microwave method, sonochemical route, and so on. Among these methods, the hydrothermal method is a typical solution-based approach that has been proven as an effective and convenient process in preparing various inorganic materials with diverse controllable morphologies and architecture in terms of cost and potential for large-scale production.9,10 The surfactantassisted hydrothermal approaches are the effective method for the synthesis of inorganic materials at relatively low temperature. Recently, tungstate compounds have attracted great interest for their applications in the fields of laser hosts, photocatalysts, x-ray intensifying screen, scintillators, etc.11,12 Double tungstates containing sodium, potassium and rare-earth ions have been extensively investigated because of their applicability in diode-pumped solid-state lasers.13–17 As novel high-quality crystals of monoclinic KLu(WO4)2, KLu(WO4)2 single crystal doped with other
rare-earth ions has been reported.18 However, except for these investigations of (Na, K)Ln(WO4)2:RE3+ single crystals, little is known about white light Eu3+-doped sodium lutetium tungstates polycrystals. Tungstates can emit blue-green light themselves under ultraviolet (UV) excitation, with Eu3+ doping, and tungstates may also effectively transfer energy to Eu3+ generating red emissions.19 Therefore, by adjusting the doping concentration of rare-earth ions, tungstates become potential white light phosphors. In the past few years, there appeared a large amount of literature corresponding to the red, blue, and green tungstate phosphor, such as Eu3+- or Tb3+-doped CaWO4,20 ZnWO4,
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