Abstract
Pure tetragonal phase, uniform and well-crystallized sodium gadolinium molybdate (NaGd(MoO4)2) nanocrystals with diverse morphologies, e.g. nanocylinders, nanocubes and square nanoplates have been selectively synthesized via oleic acid-mediated hydrothermal method. The phase, structure, morphology and composition of the as-synthesized products are studied. Contents of both sodium molybdate and oleic acid of the precursor solutions are found to affect the morphologies of the products significantly, and oleic acid plays a key role in the morphology-controlled synthesis of NaGd(MoO4)2 nanocrystals with diverse morphologies. Growth mechanism of NaGd(MoO4)2 nanocrystals is proposed based on time-dependent morphology evolution and X-ray diffraction analysis. Morphology-dependent down-shifting photoluminescence properties of NaGd(MoO4)2: Eu3+ nanocrystals, and upconversion photoluminescence properties of NaGd(MoO4)2: Yb3+/Er3+ and Yb3+/Tm3+ nanoplates are investigated in detail. Charge transfer band in the down-shifting excitation spectra shows a slight blue-shift, and the luminescence intensities and lifetimes of Eu3+ are decreased gradually with the morphology of the nanocrystals varying from nanocubes to thin square nanoplates. Upconversion energy transfer mechanisms of NaGd(MoO4)2: Yb3+/Er3+, Yb3+/Tm3+ nanoplates are proposed based on the energy level scheme and power dependence of upconversion emissions. Thermometric properties of NaGd(MoO4)2: Yb3+/Er3+ nanoplates are investigated, and the maximum sensitivity is determined to be 0.01333 K−1 at 285 K.
Highlights
Of lanthanide-doped molybdate microcrystals or phosphors[24,25,26,27,28,29]
We present a novel template-free morphology-controlled hydrothermal synthesis of NaGd(MoO4)[2] nanocrystals
Uniform and well-crystallized NaGd(MoO4)[2] nanocrystals with diverse regular morphologies can be selectively synthesized via oleic acid-mediated hydrothermal synthesis method by tuning the contents of oleic acid in the precursor solution. (MoO4)2− ions will be preferentially adsorbed on the {001} facets of tetragonal NaGd(MoO4)[2], which have a higher packing density of Gd3+/Na+ ions (0.0364 Å−2)
Summary
Of lanthanide-doped molybdate microcrystals or phosphors[24,25,26,27,28,29]. the synthesis or luminescence properties of double alkaline rare-earth molybdate nanocrystals are rarely reported, which result from the faster crystallization and growth rate and difficulty in controlling the growth process of double molybdates[30,31]. NaLa(MoO4)[2]: Eu3+, Eu3+/Tb3+ shuttle-like nanorods composed of nanoparticles were prepared hydrothermally using ethylene glycol as ligand and their luminescent properties were discussed[33,34]. Most of these works focused on either nanocrystals with only a single morphology or poor-crystallized composite nanoparticles, and controlled synthesis of double molybdates nanocrystals with diverse morphologies has not been reported so far. Uniform and well-crystallized NaGd(MoO4)[2] nanocrystals with several distinct morphologies, including nanocubes and square nanoplates, can be selectively synthesized by a modified hydrothermal method using oleic acid as complexing agent. Morphology-dependent down-shifting photoluminescence properties of NaGd(MoO4)[2]: Eu3+ nanocrystals, upconversion photoluminescence properties of Yb3+/Er3+ and Yb3+/Tm3+ square nanoplates, and thermometric properties of NaGd(MoO4)[2]: Yb3+/Er3+ square nanoplates are investigated in detail
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