Shanshan Hu

Controllable synthesis of Sc2Mo3O12 microcrystals with exposed {001} facets and their remarkable tunable luminescence properties by doping lanthanides

Novel chocolate-like scandium molybdate precursors with exposed {001} facets were hydrothermally synthesized in the presence of PVP, which were transformed into morphology-preserved Sc2Mo3O12 crystals by calcination at 800 °C for 2 h. The as-synthesized samples were characterized by XRD, FT-IR SEM, TEM, HRTEM, and PL analysis. Four different types of precursors including prismatic structures, octahedra, truncated octahedra and compressed decahedra could be obtained by varying the amount of MoO42−. Moreover, in the presence of H+, the percentage of high-energy {001} facets could be enhanced. The Mo sources, PVP consumption, reaction time and hydrothermal temperature had significant influences on the morphology of the precursors. As good matrix materials, the tunable down/upconversion (DC/UC) luminescence properties of Sc2Mo3O12:Ln3+ (Ln = Tb, Eu, Tb/Eu, Yb/Er, Yb/Ho, Yb/Tm) were comprehensively investigated. It is found that the materials showed strong morphology-dependent luminescence properties. Particularly, the energy transfer (ET) of MoO42− → Tb3+ → Eu3+ resulted in multicolor emissions from green to red in Sc2Mo3O12:5%Tb3+,x%Eu3+. The Sc2Mo3O12:Ln3+ (Ln = Tb, Eu, Tb/Eu, Yb/Er, Yb/Ho, Yb/Tm) microcrystals show great potential applications in the areas of fluorescent lamps and color displays.

Shape-controllable hydrothermal synthesis of NaTbF4:Eu3+ microcrystals with energy transfer from Tb to Eu and multicolor luminescence properties

Hexagonal NaTbF4 microplates have been successfully synthesized through a simple hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), inductively coupled high frequency plasma atomic emission spectroscopy (ICP-AES), photoluminescence (PL) and luminescence decay curves were used to characterize the samples. By optimizing the experimental conditions, such as Na-citrate consumption, pH value, reaction time and hydrothermal temperature, we obtained the samples with different components (NaTbF4, TbF3), crystal phases (α-NaTbF4, β-NaTbF4), and morphologies. A possible formation mechanism for the samples with different structures was proposed. In addition, the monodisperse hexagonal NaTbF4 microplates, which can be used as an excellent host lattice for Eu3+ ions, and the multicolor luminescence properties of NaTbF4 with various Eu3+ doping concentrations have been studied. At the same time, the energy transfer from Tb3+ to Eu3+ in NaTbF4:x%Eu3+ (x = 0–1) was also investigated. The color of the NaTbF4:x%Eu3+ (x = 0–1) samples can be varied from green to red by adjusting the doping concentration of Eu3+, which exhibits a good advantage of multicolor emissions in the visible region, and endows this material with potential application in many fields, such as light display systems, optoelectronic devices and biological imaging. Such a simple synthetic method is also useful for the synthesis of other complex rare earth fluorides with hexagonal architectures.

Lanthanide-doped Sr2ScF7 nanocrystals: controllable hydrothermal synthesis, the growth mechanism and tunable up/down conversion luminescence properties

Sr2ScF7:Ln3+ (Ln = Ce, Tb, Eu, Sm, Dy, Er, Tm, Ho and Yb) nanocrystals were firstly synthesized via a one-step hydrothermal route without employing any surfactants. The shape and size of the Sr2ScF7 nanocrystals could be readily tuned from nanorods with 120 nm length and 50 nm width to nanoparticles with a uniform diameter of 15 nm by doping 30% Ln3+ with a larger ionic radius. Furthermore, the influence of pH values, F− sources and different surfactants on the sizes and morphologies (including nanorods, quadrangular microplates, cubes and polyhedrons) of the as-prepared products was systematically investigated and the possible formation mechanism for the products has been proposed. The XRD, SEM, EDS, PL analysis and decay lifetimes were used to characterize the products. For DC photoluminescence, the Sr2ScF7:Ln3+ nanocrystals show the characteristic f–f transitions with emission colors of bluish violet (Ce3+, Tm3+), green (Tb3+, Er3+, Ho3+), blue (Dy3+) and orange (Eu3+, Sm3+) respectively. Under single wavelength 980 nm excitation, the blue UC emissions of Sr2ScF7:Yb3+,Tm3+ nanocrystals at 474 nm due to the 1G4 → 3H6 transition of Tm3+, the green UC emissions of Sr2ScF7:Er3+ nanocrystals at 522/544 nm assigned to the 2H11/2 → 4I15/2/4S3/2 → 4I15/2 transitions and the red UC emissions of Sr2ScF7:Yb3+,Er3+ at 660 nm from 4F9/2 → 4I15/2 transition of Er3+ were observed. Based on the generation of red, green, and blue emissions, the Sr2ScF7:Yb3+,Er3+,Tm3+ nanocrystals could produce multicolor, particularly in the white region (0.320, 0.330) by controlling the doping concentration of Tm3+ in the Sr2ScF7:Yb3+,Er3+,Tm3+ nanocrystals. Controlling the doping concentration of Tm3+ is an effective way of modulating the luminescence properties of Sr2ScF7:Ln3+ by controlling its size and morphology. The as-synthesized phosphors might be potentially applied in the fields of color displays, light, photonics and biological imaging.

One-step hydrothermal synthesis of Sc2Mo3O12:Ln3+ (Ln = Eu, Tb, Dy, Tb/Eu, Dy/Eu) nanosheets and their multicolor tunable luminescence

Novel Sc2Mo3O12:Ln3+ (Ln = Eu, Tb, Dy, Tb/Eu, Dy/Eu) phosphors have been synthesized via a one-step hydrothermal route using glycine (Gly) as a surfactant. The phosphors were characterized using X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), photoluminescence (PL), and luminescence decays. It was found that various surfactants had a profound influence on the crystal phase, morphology and emission intensity of the final products. Furthermore, the photoluminescence of Ln3+-doped Sc2Mo3O12 phosphors (Ln = Eu, Tb, Dy, Tb/Eu, Dy/Eu) was studied in detail. The energy transfer of MoO42− → Tb3+ (Dy3+) → Eu3+ and multicolor tunable emission occurred by changing the ratio of Tb3+/Eu3+ or Dy3+/Eu3+ under single wavelength excitation. Moreover, the energy transfer mechanism from Tb3+ (Dy3+) to Eu3+ was ascribed to dipole–dipole interactions and the energy transfer efficiency from Tb3+ to Eu3+ (95.3%) was higher than that from Dy3+ to Eu3+ (87.5%). Their tunable multicolor luminescence properties make Sc2Mo3O12:Ln3+ (Ln = Eu, Tb, Dy, Tb/Eu, Dy/Eu) phosphors suitable for many potential applications in the fields of color displays and fluorescent lamps.

Tuning the phase, morphology and size of monodisperse ScF3 and NaScF4 crystals through lanthanide doping

Monodisperse ScF3 and NaScF4 nano-/micro-crystals were prepared by a simple solvothermal method. There were many important factors including the molar ratio of Na/F/(Sc + Ln) and Ln3+ doping to control the synthesis of the products. A phase transformation from monoclinic ScF3 to hexagonal NaScF4 was observed with different molar ratios of Na/F/Sc. Herein, the products doped with 1% Ln3+ (La–Lu, except Pm) demonstrated abundant phases, morphologies and sizes. Moreover, the products with different Lu3+ doping concentrations from 1% to 60% were prepared. The results revealed that different kinds of 1% Ln3+ (La–Lu, except Pm) and diverse concentrations of Lu3+ can modify the phase, morphology and size of the prepared products. A possible formation mechanism for the products with diverse morphologies is proposed. In addition, Ln3+-doped ScF3 or NaScF4 nano-/micro-crystals presented characteristic up/down-conversion fluorescence spectra.

Morphology-controlled synthesis and luminescence properties of ScPO4·2H2O:Ln3+ nano/micro-crystals by a facile approach

Well-crystallized and uniform ScPO4·2H2O and ScPO4·2H2O:Ln3+ (Ln = Ce, Eu, Tb, Lu) nano/micro-crystals with multiform morphologies, such as sphere, hexagonal plate, diamond, four-angle star, butterfly-shaped and cuboid, have been successfully synthesized by a facile hydrothermal route without any surfactant molecules. XRD, FE-SEM, TEM, PL and kinetic decay were used to characterize the as-prepared products. The size and morphology of ScPO4·2H2O can be determined by the pH value, reaction time, reaction temperature, additive and doping of lanthanide ions. In particular, Ln3+ doping not only has a crucial role in the morphology of ScPO4·2H2O, but also affects its luminescence properties. The ScPO4·2H2O:Tb3+ and ScPO4·2H2O:Ce3+ samples display intense green and blue emissions, respectively. More importantly, the luminescence properties are closely related to morphologies and crystallinity. It can be found that the ScPO4·2H2O:Tb3+ sample with a hexagonal plate-like morphology possesses much higher emission intensity than those with other morphologies because of its larger anisotropic geometry. ScPO4:Ln3+ crystals will become promising candidates for a variety of applications in down/up-conversion luminescence, magnets, lasers, and bio-labeling.

One-step surfactant-free synthesis of Eu3+-activated NaTb(MoO4)2 microcrystals with controllable shape and their multicolor luminescence properties

Uniform NaTb(MoO4)2 (NTM) microcrystals with controllable morphologies were synthesized via a facile one-step hydrothermal route without employing any templates or surfactants. Diverse morphologies were achieved by manipulating the crystal growth environment; particularly, by increasing the amount of Na2MoO4, uniform and well-defined NTM microcrystals with bipyramid, truncated bipyramid, quasi-cube and thin plate shapes were achieved, and the mechanism of this variation was due to the strong electrostatic interaction between MoO42− and Tb3+/Na+. In addition, multicolor emissions (green → yellow → red) of NTM:Eu3+ phosphors were obtained by merely adjusting the Eu3+ doping content, which resulted from the efficient energy transfer (ET) from MoO42− to Tb3+ and then to Eu3+. Further research revealed that the efficient ET mechanism (Tb3+ → Eu3+) was dominated by the dipole–quadrupole interaction. It was found that the larger crystal shape/size could greatly enhance their luminescence properties, resulting from their high crystallinity and few defects on the crystal surfaces. The as-synthesized phosphors might be potentially applied in multicolor lighting and displays.

Facile hydrothermal synthesis of Tb2(MoO4)3:Eu3+ phosphors: controllable microstructures, tunable emission colors, and the energy transfer mechanism

Microsphere-like Tb2(MoO4)3 structures have been successfully synthesized by a facile hydrothermal method with the subsequent calcination treatment. The shape and size of the microstructure of Tb2(MoO4)3 precursors can be tuned effectively by altering the amount of citric acid, and the possible formation mechanisms of various microstructures are also put forward, showing that citric acid plays a key role in controlling the morphologies of the precursors. By doping Eu3+, Tb2(MoO4)3:Eu3+ phosphors exhibit excellent luminescence properties with tunable emission colors (green → yellow → red) resulting from the effective energy transfer from Tb3+ to Eu3+. Particularly, the energy transfer mechanism (Tb3+ → Eu3+) has also been investigated in detail, showing that the process mainly takes place via the dipole–dipole interaction based on a few theoretical simulations. Due to the facile preparation process, as well as intense tunable emission colors, these novel phosphors are expected to find a broad range of applications in future color displays and light-emitting devices.

Self-assembled hierarchical architecture of tetragonal AgLa(MoO4)2 crystals: hydrothermal synthesis, morphology evolution and luminescence properties

Tetragonal AgLa(MoO4)2 microcrystals with novel discal hierarchical architectures were successfully synthesized via a one-step hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and photoluminescence (PL) spectral analysis as well as decay lifetimes were employed to characterize the prepared products. It was found that various hierarchical architectures were obtained by altering the amount of MoO42−, pH values and surfactants, respectively. In particular, the pH value had a large influence not only on the morphology, but also on the size and crystallinity. The formation mechanism of discal hierarchical architectures was proposed on the basis of the self-assembly growth of nanosheets. The AgLa(MoO4)2 microcrystals exhibited excellent down/up-conversion (DC/UC) multicolor emissions after doping different Ln3+ ions. For DC luminescence, AgLa(MoO4)2:Ln3+ (Ln = Eu, Tb, Sm, Dy) exhibited characteristic red emission, green emission, orange emission and yellow emission, respectively. The energy transfer of MoO42− → Ln3+ (Ln = Tb, Sm, Dy) markedly enhanced the characteristic emissions of Tb3+, Sm3+ and Dy3+. For UC luminescence, AgLa(MoO4)2:Yb3+/Ln3+ (Ln = Er, Tm, Ho) exhibited intense green (2H11/2 → 4I5/2 of Er3+), blue (1G4 → 3H6 of Tm3+), yellow (5F5 → 5I8 of Ho3+) emissions, respectively. Therefore, the as-prepared AgLa(MoO4)2:Ln3+ microcrystals may have potential application to serve as fluorescent lamps, field emission display devices, sensors and biological imaging agents.

One-step surfactant-free synthesis of KSc2F7 microcrystals: controllable phases, rich morphologies and multicolor down conversion luminescence properties

Homogeneous KSc2F7 microcrystals with controlled and abundant morphologies were prepared by a one-step hydrothermal route without employing any templates or surfactants. Particularly, uniform and well-defined KSc2F7 crystals with rod, sheet, flower-like, thin rectangular, xylitol-like and thin plate morphologies were achieved by manipulating the different environments of crystal growth, such as increasing the concentration of F−, changing pH and adding different surfactants. In addition, a phase transformation from monoclinic ScF3 to orthorhombic KSc2F7 was observed at different molar ratios of F/Sc and pH values, respectively. A more interesting thing is that the KSc2F7 crystals doped with 5% Ln3+ (Ln = La, Ce, Sm, Eu, Gd, Tb and Lu) showed rich morphologies and various sizes. The obtained KSc2F7:Ln3+ products showed multicolor emission with red (Eu3+), green (Tb3+) and blue (Ce3+), respectively. And the best emission conditions for KSc2F7 crystals are F/Sc/K = 3.5 : 1 : 3, pH = 7 and without any surfactants. The synthetic KSc2F7:Eu3+/Tb3+/Ce3+ phosphors may potentially be used for multicolor illumination and displays.