CaF2:Ln3+ (Ln = Ce, Tb, Eu) phosphors with highly uniform shapes have been successfully synthesized by a simple hydrothermal method directly. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) and lifetime. The results indicated that the pH values, organic additive and reaction time have a significant effect on the morphology and dimensions of CaF2 microcrystals and the possible formation mechanism was also proposed. Furthermore, the energy transfer from Ce3+ to Tb3+ and from Tb3+ to Eu3+ and from Ce3+ to Tb3+ to Eu3+ was observed and the corresponding mechanisms were discussed in detail. The CaF2:Ln3+ phosphors may have potential optical applications in near-UV and violet LEDs.

Ba3Sc2F12:Yb3+, Ln3+ (Ln = Er, Ho, Tm) crystals with various morphologies have been synthesized via a one step hydrothermal route. X-ray diffraction (XRD), scanning electron microscopy (SEM), and up conversion photoluminescence (UCPL) spectra were used to characterize the samples. The influences of surfactants, pH values, and molar ratio of F−/Sc3+ on the crystal phase, size and shape of final products have been studied in detail. The aspect ratio of products increased gradually with the increase of F−/Sc3+ molar ratio. Additionally, the luminescence properties of Ba3Sc2F12:Yb3+, Ln3+ (Ln = Er, Ho, Tm) crystals were systematically studied. The blue emission is attributed to the 1G4 → 3H6 transition of Tm3+; the green emission can be obtained due to the 2H11/2/4S3/2 → 4I15/2 transitions of Er3+ and the 5S2/5F4 → 5I8 transition of Ho3+; the red emission comes from the 4F9/2 → 4I15/2 transition of Er3+ and the 1G4 → 3F4 transition of Tm3+. Based on the generation of red, green, and blue emissions in the different Ln ion-doped Ba3Sc2F12, the white light emission can be obtained by appropriately doping Yb3+, Er3+, and Tm3+ in the present Ba3Sc2F12 crystals due to the color superposition principle. Here, the sample Ba3Sc1.5856F12:0.4Yb3+, 0.01Er3+, 0.0044Tm3+ crystals showed suitable intensity ratio of blue, green and red (RGB) emissions resulting in bright white light with CIE-x = 0.274 and CIE-y = 0.287, which was illustrated by a photograph under excitation of 980 nm. The prepared Ba3Sc2F12:Ln3+ phosphor has potential applications in the fields of three dimensional displays, back lighting and white light sources.

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.

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.

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.

Crystalline Tb2(CO3)3: Eu3+ samples were successfully synthesized by the precipitation reaction of rare-earth chloride with ammonium bicarbonate in solution directly under mild condition without further thermal treatment. The samples were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetry analysis, Fourier transform infrared spectroscopy, photoluminescence, as well as lifetimes. Influences of pH, molar ratio of precipitant to rare earth ions, aging time, temperature, and surfactant on the morphology and crystal structure were investigated in detail. The obtained samples presented dumbbell-like microstructures which were assembled from nanosheets with the assistance of ethylene glycol. Under the excitation of 220-nm ultraviolet light, the Tb2(CO3)3 samples showed the characteristic emissions of Tb3+ corresponding to 5D4 → 7F6,5,4,3 transitions, whereas the Tb2(CO3)3: Eu3+ samples mainly exhibited the characteristic emissions of Eu3+ corresponding to 5D0 → 7F0,1,2,3,4 transitions due to an effective energy transfer from Tb3+ to Eu3+. The energy transfer efficiency from Tb3+ to Eu3+ increased with Eu3+ doping concentration. The multicolor emission of Tb2(CO3)3: Eu3+ samples can be tuned from green to red easily by altering the doping concentration of Eu3+. The materials are expected to apply widely in the future, and the simple method is particularly suitable for large-scale industrial production.

•We firstly described a (WAl)C–Co/fluoride composites prepared by powder metallurgy.•(WAl)C–Co/fluoride hard materials possess good mechanical property.•The friction coefficient of (W0.67Al0.33)C0.67–Co/fluoride composite is 0.22–0.36.•We firstly studied the lubrication mechanism of (W0.67Al0.33)C0.67–Co/fluoride.(WAl)C–Co/fluoride (CaF2, BaF2, CaF2/BaF2) self-lubricating ceramic composites prepared by mechanical alloying and hot pressing sintering was reported for the first time. The influence of the fluorides on the mechanical properties, friction coefficient and wear rate of the composites was also evaluated. The friction coefficient of the (W0.67Al0.33)C0.67–Co/fluoride materials is in the range of 0.22–0.36, with the wear rate in the order of 10− 6 mm3 N− 1 m− 1. The fluoride in the (W0.67Al0.33)C0.67–Co/fluoride plays a key role in decreasing the friction coefficient and wear rate. The wear layer formed during friction process exerts a significant influence on the tribological properties, which would increase the friction coefficient but protect the worn surface.

Uniform and dispersive Lu2O3:Yb3+/Er3+/Tm3+ nanocubes have been successfully synthesized by hydrothermal process with subsequent calcination at 900 °C. The as-formed RE3+-doped lutetium oxide precursor via the hydrothermal process, as a template, could transform to RE3+-doped Lu2O3 with their original cubic morphology and slight shrinkage in the size after post-annealing process. The formation mechanism for the lutetium oxide precursor cubes has been proposed. Under single wavelength diode laser excitation of 980 nm, the as-obtained Lu2O3:3%Yb3+/0.5%Er3+/0.3%Tm3+ nanocubes show nearly equal intensities of blue (Tm3+: 1G4 → 3H6), green (Er3+: (2H11/2, 4S3/2) → 4I15/2), and red (Er3+: 4F9/2 → 4I15/2) emissions, which produces bright white light emission, clearly visible to the naked eyes. The main pathways to populate the upper emitting states come from the energy-transfer processes from Yb3+ to Tm3+/Er3+, respectively. The chromaticity coordinate of the Lu2O3:3%Yb3+/0.5%Er3+/0.3%Tm3+ sample is calculated to be about x = 0.3403 and y = 0.3169, which falls exactly within the white region of 1931 CIE diagram and is very close to the standard equal energy white light illuminate (x = 0.33 and y = 0.33), pointing out its potential use as a white light source under 980 nm laser diode excitation.Graphical abstractHighlights► Uniform and dispersive cubic precursor can be synthesized by sample hydrothermal process. ► Hydrothermal precursor could transform to Lu2O3:RE3+ with its original cubic morphology. ► Nearly equal intensities of blue, green, and red emissions under single 980 nm laser. ► Lu2O3:RE3+ show bright white light emission, clearly visible to the naked eyes. ► Chromaticity coordinate is very close to the standard equal energy white light illuminate.

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.