beta-NaYF4:Ln3+ (Ln = Eu, Tb, Yb/Er, and Yb/Tm) hexagonal microprisms with remarkably uniform morphology and size have been synthesized via a facile hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra as well as kinetic decays were used to characterize the samples. It is found that sodium citrate as a shape modifier introduced into the reaction system plays a critical role in the shape evolution of the final products. Furthermore, the shape and size of the products can be further manipulated by adjusting the molar ratio of citrate/RE3+ (RE represents the total amount of Y3+ and the doped rare earth elements such as Eu3+, Tb3+, Yb3+/Er3+, or Yb3+/Tm3+). Under the excitation of 397 nm ultraviolet light, NaYF4:xEu3+ (x = 1.5, 5%) shows the emission lines of Eu3+ corresponding to 5D0-3 --> 7FJ (J = 0-4) transitions from 400 to 700 nm (whole visible spectral region) with different intensity, resulting in yellow and red down-conversion (DC) light emissions, respectively. When doped with 5% Tb3+ ions, the strong DC fluorescence corresponding to 5D4 --> 7FJ (J = 6, 5, 4, 3) transitions with 5D4 --> 7F5 (green emission at 544 nm) being the most prominent group that has been observed. In addition, under 980 nm laser excitation, the Yb3+/Er3+- and Yb3+/Tm3+-codoped beta-NaYF4 samples exhibit bright green and whitish blue up-conversion (UC) luminescence, respectively. The luminescence mechanisms for the doped lanthanide ions were thoroughly analyzed.

NaYF 4 microcrystals with a variety of morphologies, such as microrod, hexagonal microprism, and octadecahedron, have been synthesized via a facile hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) spectra were used to characterize the samples. The intrinsic structural feature of -NaYF 4 seeds and two important external factors, namely, the pH values in the initial reaction solution and fluoride sources, are responsible for shape determination of -NaYF 4 microcrystals. It is found that the organic additive trisodium citrate (Cit 3-) as a shape modifier has the dynamic effect by adjusting the growth rate of different facets under different experimental conditions, resulting in the formation of the anisotropic geometries of various -NaYF 4 microcrystals. The possible formation mechanisms for products with various architectures have been presented. A systematic study on the photoluminescence of Tb 3+ -doped -NaYF 4 samples with rod, prism, and octadecahedral shapes has shown that the optical properties of these phosphors are strongly dependent on their morphologies and sizes. This synthetic methodology appears to be general and promises to provide a gateway into other rare earth fluoride compounds.

Indium hydroxide, In(OH)3, nano-microstructures with two kinds of morphology, nanorod bundles (around 500 nm in length and 200 nm in diameter) and caddice spherelike agglomerates (around 750-1000 nm in diameter), were successfully prepared by the cetyltrimethylammonium bromide (CTAB)/water/cyclohexane/n-pentanol microemulsion-mediated hydrothermal process. Calcination of the In(OH)3 crystals with different morphologies (nanorod bundles and spheres) at 600 degrees C in air yielded In2O3 crystals with the same morphology. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence (PL) spectra as well as kinetic decays were used to characterize the samples. The pH values of microemulsion play an important role in the morphological control of the as-formed In(OH)3 nano-microstructures from the hydrothermal process. The formation mechanisms for the In(OH)3 nano-microstructures have been proposed on an aggregation mechanism. In2O3 nanorod bundles and spheres show a similar blue emission peaking around 416 and 439 nm under the 383-nm UV excitation, which is mainly attributed to the oxygen vacancies in the In2O3 nano-microstructures.

Hydroxyapatite (Ca 5 (PO 4 ) 3 OH) nano-and microcrystals with multiform morphologies (separated nanowires, nanorods, microspheres, microflowers, and microsheets) have been successfully synthesized by a facile hydrothermal process. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) spectra, kinetic decay, and electron paramagnetic resonance (EPR) were used to characterize the samples. The experimental results indicate that the obtained Ca 5 (PO 4 ) 3 OH samples show an intense and bright blue emission under long-wavelength UV light excitation. This blue emission might result from the CO 2•radical impurities in the crystal lattice. Furthermore, the organic additive (trisodium citrate) and pH values have an obvious impact on the morphologies and luminescence properties of the products to some degree. The possible formation and luminescent mechanisms for Ca 5 (PO 4 ) 3 OH nano-and microcrystals are presented in detail.

Lanthanide fluoride LnF 3 (Ln ) La to Lu) nano-/microcrystals with multiform crystal structures (hexagonal and orthorhombic) and morphologies (separated elongated nanoparticles, aggregated nanoparticles, polyhedral microcrystals) were successfully synthesized by a facile, effective, and environmentally friendly hydrothermal method. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and photoluminescence spectra were used to characterize the samples. The experimental results indicated that the use of NaBF 4 is indispensable for obtaining LnF 3 crystal structures. Furthermore, the organic additive trisodium citrate (Cit 3-) has an obvious impact on the morphologies of the products to some degree. The possible formation mechanisms for LnF 3 nano-/microcrystals are presented in detail. Additionally, we systematically investigated the luminescence properties of the LnF 3 :Eu 3+ (Ln ) La, Gd, and Lu) samples and found an efficient energy transfer from Gd 3+ to Eu 3+ in GdF 3 :Eu 3+ .

Nearly monodisperse and well-defined one-dimensional (1D) Gd 2 O 3 :Eu 3+ nanorods and microrods were successfully prepared through a large-scale and facile hydrothermal method followed by a subsequent heat treatment process, without using any catalyst or template. X-ray diffraction (XRD), thermogravimetric analysis and differential scanning calorimetry (TGA-DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), photoluminescence (PL) and cathodoluminescence (CL) spectra as well as kinetic decays were used to characterize the samples. The size of the Gd 2 O 3 :Eu 3+ rods could be modulated from micro-to nanoscale with the increase of pH value using ammonia solution. The as-formed product via the hydrothermal process, Gd(OH) 3 :Eu 3+ , could transform to cubic Gd 2 O 3 :Eu 3+ with the same morphology and a slight shrinking in size after a postannealing process. The formation mechanism for the Gd(OH) 3 rods has been proposed. Both the Gd 2 O 3 :Eu 3+ nanorods and microrods exhibit the same strong red emission corresponding to 5 D 0 f 7 F 2 transition (610 nm) of Eu 3+ under UV light excitation (257 nm) and low-voltage electron beam excitation (1-5 kV), which have potential applications in fluorescent lamps and field emission displays.

Three-dimensional flowerlike Lu 2 O 3 and Lu 2 O 3 :Ln 3+ (Ln ) Eu, Tb, Dy, Pr, Sm, Er, Ho, Tm) microarchitectures have been successfully synthesized via ethylene glycol (EG)-mediated hydrothermal method followed by a subsequent heat treatment process. X-ray diffraction, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectra, thermogravimetric and differential thermal analysis, elemental analysis, inductively coupled plasma atomic absorption spectrometric analysis, ion chromatogram analysis, X-ray photoelectron spectra, scanning electron microscopy, transmission electron microscopy, photoluminescence spectra as well kinetic decays, and cathodoluminescence spectra were used to characterize the samples. Hydrothermal temperature, EG, and CH 3 COONa play critical roles in the formation of the lutetium oxide precursor microflowers. The reaction mechanism and the self-assembly evolution process have been proposed. The as-formed lutetium oxide precursor could transform to Lu 2 O 3 with their original flowerlike morphology and slight shrinkage in the size after postannealing process. The as-obtained flowerlike Lu 2 O 3 :Ln 3+ samples show strong light emission with different colors corresponding to different Ln 3+ ions under ultraviolet-visible light excitation and lowvoltage electron beams excitation, which have potential applications in fluorescent lamps and field emission displays.

Y2O3 :  Eu3+ microspheres, with an average diameter of 3 μm, were successfully prepared through a large-scale and facile solvothermal method followed by a subsequent heat treatment. X-ray diffraction, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectra, thermogravimetric and differential thermal analysis, inductive coupled plasma atomic absorption spectrometric analysis, scanning electron microscopy, transmission electron microscopy, photoluminescence spectra, as well kinetic decays, and cathodoluminescence spectra were used to characterize the samples. These microspheres were actually composed of randomly aggregated nanoparticles. The formation mechanisms for the Y2O3 :  Eu3+ microspheres have been proposed on an isotropic growth mechanism. The Y2O3 :  Eu3+ microspheres show a strong red emission corresponding to 5 D 0 → 7 F 2 transition (610 nm) of Eu3+ under ultraviolet excitation (259 nm) and low-voltage electron beams excitation (1−5 kV), which have potential applications in fluorescent lamps and field emission displays.