Shuangyu Xin

Recent development in rare earth doped phosphors for white light emitting diodes

As new light sources for next-generation illumination, white light-emitting diodes (WLEDs) have been extensively developed and are commercially available due to their excellent advantages, such as high efficiency, energy-saving, compactness, long operational lifetime and environmental friendliness. Currently, WLEDs with high color rendering are mainly based on wavelength conversion by one or more phosphor materials. In this review, the recent developments of phosphors for WLEDs were introduced combined with the relative work of our group. The common methods for generating white light for blue/ultraviolet (UV) WLEDs were summarized, including: (1) optimizing the commercially used phosphors; (2) developing some new phosphors based on UV LEDs chips; (3) realizing white light emission based on single host. Moreover, some typical new developed phosphors and their luminescence properties were introduced.

Facile synthesis and optical properties of nitrogen-doped carbon dots

Among the chemical doping elements, nitrogen atoms play a critical role in tuning the intrinsic properties or exploiting new phenomena of carbonaceous materials. Herein, we report a facile strategy to synthesize nitrogen-doped carbon dots (NCDs) using glutamic acid as the precursor via a one-step thermal conversion process. The as-produced NCDs exhibit bright blue photoluminescence (the quantum yield of ca. 23.2%), and the emission wavelength could be slightly tuned through changing the parameters of the synthesizing process. Interestingly, apart from their superior luminescence characters, unexpected cathodoluminescence (CL) and frequency upconverted emission properties were both observed in the NCDs.

Preparation and drug-delivery properties of hollow YVO4:Ln3+ and mesoporous YVO4:Ln3+@nSiO2@mSiO2 (Ln = Eu, Yb, Er, and Ho)

In this paper, size-controlled morphologies of (Y, Gd)VO4 and (Y, Gd)VO4:Ln3+ (Ln = Eu, Yb, Er, and Ho) were obtained via a facile hydrothermal route, and their properties for drug delivery and photoluminescence were investigated. Monodisperse ellipsoid-like hollow (Y, Gd)VO4 were designed by employing (Y, Gd)(OH)CO3 colloidal spheres as a sacrificial template and NH4VO3 as a vanadium source, and the formation mechanism could be interpreted by the Kirkendall effect. The control of particle size for hollow (Y, Gd)VO4 was realized, facilitating their practical application. Mesoporous core-shell structured (Y, Gd)VO4:Ln3+@nSiO2@mSiO2 were designed to improve the properties for drug release. Typically, red emission of YVO4:Eu3+ predominated under 465 nm excitation; the upconversion spectra of YVO4:Yb3+, Er3+ and YVO4:Yb3+, Ho3+ revealed green and red color upon 980 nm excitation, respectively. The biocompatibility and drug release evaluations indicate the potential biological applications of the samples.

A new type of color tunable composite phosphor Y2SiO5:Ce/Y3Al5O12:Ce for field emission displays

A simple but effective strategy was introduced to realize color tunability of a composite phosphor Y2SiO5:Ce/Y3Al5O12:Ce (YSO:Ce/YAG:Ce). The main idea was to use the cathodoluminescence of the YSO:Ce phosphor to additionally pump the photoluminescence of the YAG:Ce phosphor based on radiative energy transfer. Morphology as well as the cathodoluminescence properties of the YSO:Ce/YAG:Ce phosphors were investigated in detail. According to radiative energy transfer, an intense yellow emission with excellent cathodoluminescence properties can be obtained from YSO:Ce/YAG:Ce phosphors under low voltage electron beam excitation. Moreover, the emission color of the composite phosphors can be tuned from yellow to blue through adjusting the YSO:Ce content. The mechanism for the enhanced yellow emission and the color tunability were also discussed. It was experimentally proved that the color gamut and display hue could be greatly enriched and enhanced when employing the YSO:Ce/YAG:Ce composite phosphor as an additional phosphor for the typical tricolor FED phosphors.

Crystal structure and luminescence properties of a cyan emitting Ca10(SiO4)3(SO4)3F2:Eu2+ phosphor

Europium-doped apatite Ca10(SiO4)3(SO4)3F2 (CSSF) has been successfully synthesized by solid state reaction. The crystal structure of CSSF:0.006Eu2+ is refined by the Maud refinement method. Optical properties of the prepared samples are found to depend on the rare-earth metal–oxygen distances and lattice iconicity. The excitation spectra of the CSSF:Eu2+ phosphors centered at 350 nm and covered the range from 250 to 450 nm. Under 350 nm excitation, the emission spectra of CSSF:Eu2+ phosphors show a blue (centered at 420 nm) and a green (centered at 525 nm) emission band, respectively. Meanwhile, the concentration quenching and energy transfer mechanism have been investigated via the configuration coordinate diagram. The key parameters, such as the temperature-dependent photoluminescence and CIE values of the CSSF:Eu2+ phosphor have also been studied.

Multicolor bright Ln 3+ (Ln = Eu, Dy, Sm) activated tungstate phosphor for multifunctional applications

A series of multifunctional phosphors Y2WO6: Ln3+ (Ln = Eu, Sm, Dy) were prepared by solid state reaction. The phase purity, luminescent properties and energy transfer from WO66- to Ln3+ are investigated by the X-ray diffractometer, photoluminescence and cathodoluminescence spectra, as well as decay lifetimes, respectively. The band gap of Y2WO6 is calculated to be about 3.139 eV, in agreement with the value of 3.184 eV obtained from the reflection spectrum. When excited by vacuum ultra violet light at 147 nm, the emission intensity of Y2WO6: Eu3+ can reach 66% of that of commercial (Y,Gd)BO3: Eu3+ (KX-504A), and Y2WO6: Dy3+ and Y2WO6: Sm3+ show white light emission. The white light emission can also be obtained under ultraviolet excitation at 319 nm. Under the electron beam excitation, the Y2WO6: Sm3+, Y2WO6: Dy3+ and Y2WO6: Eu3+ show tunable white, blue and red emissions with excellent degradation properties, respectively. These results reveal that the Y2WO6: Eu3+, Y2WO6: Sm3+ and Y2WO6: Dy3+ may have potential applications in three-dimensional plasma display panels, light-emitting diodes and field emission displays.

Synthesis and up-conversion luminescence of Yb3+/Er3+/Tm3+ doped Ca9Y(PO4)7

Samples of Ca9Y(PO4)7 co-doped with Yb3+/Er3+, Yb3+/Tm3+, or Yb3+/Er3+/Tm3+ have been synthesized through two different routes, i.e. a modified hydrothermal method, followed by annealing in air at 850 °C and a solid-state reaction. The results of SEM and TEM show that the particle size of the samples synthesized by the solid state reaction method is about several micrometers, while that of the sample synthesized by the modified hydrothermal method is around 180 nm. The up-conversion luminescence of samples is studied as a function of different Yb3+, Er3+, Tm3+ ion concentrations and laser powers. Under 980 nm laser excitation, samples of Yb3+/Er3+ co-doped Ca9Y(PO4)7 generate green and red emissions, while samples co-doped by Yb3+/Tm3+ generate blue and red emissions. The red emission is most intense in Yb3+/Er3+ co-doped samples, while blue emission is predominant in Yb3+/Tm3+ co-doped samples. The main mechanism that allows for the up-conversion observed in Yb3+/Er3+, Yb3+/Tm3+ or Yb3+/Er3+/Tm3+ doped Ca9Y(PO4)7 is attributed to the energy transfer among Yb3+ and the various Er3+/Tm3+ ions in excited states.

The pure-phase Ba3−xCaxSi6O12N2:Eu2+ green phosphor: synthesis, photoluminescence and thermal properties

The promising green oxynitride phosphor, Ba3−xCaxSi6O12N2:Eu2+, was synthesized at 1350 °C for 5 hours under a reducing N2/H2 (5%) atmosphere via the solid-state reaction method. The XRD patterns confirm the formation of the pure phase of Ba3−xCaxSi6O12N2:Eu2+. With an increase in x, the emission spectra shift from 525 nm to 536 nm under near-UV (n-UV) excitation. Accordingly, we propose the underlying mechanisms for the red-shift of the emission spectra by adjusting the cation composition in the host. The influence of the size mismatch on the thermal quenching is also observed. The as-prepared green phosphor exhibits great thermal quenching property, with the remaining 83% of the initial emission intensity measured at 150 °C. The quantum efficiency is measured to be 35.2%. All the results indicate that the Ba3−xCaxSi6O12N2:Eu2+ can be a good candidate phosphor applicable to n-UV light-emitting diodes for solid-state lighting.

Preparation, characterization, and luminescent properties of CaAl2O4:Eu2+, Nd3+ nanofibers using core–sheath CaAl2O4:Eu2+, Nd3+/carbon nanofibers as templates

CaAl2O4:Eu2+, Nd3+ nanofibers were prepared via the electrospinning process by using core–sheath CaAl2O4:Eu2+, Nd3+/carbon nanofibers as templates, combined with a subsequent annealing treatment. The obtained nanofibers are smooth with tunable diameters ranging from 50 to 120 nm by simply changing the ratio of inorganic precursors to solvent. The intermediate state is composed of hollow CaAl2O4:Eu2+, Nd3+@carbon nanofibers. The formation process, luminescent properties and long lasting performance are investigated. This facile method for synthesizing nanofibers may have potential applications in the field of in vivo imaging and coatings for long lasting phosphors.

A simple way to synthesize well-dispersed Gd{sub 2}O{sub 3} nanoparticles onto reduced graphene oxide sheets

Graphical abstract: Display Omitted Highlights: ► A simple approach to obtain Gd{sub 2}O{sub 3} nanoparticles onto RGO sheets. ► Gd{sub 2}O{sub 3} nanoparticles could be bonded with RGO by the residual C-OH or COOH groups. ► The as-prepared Gd{sub 2}O{sub 3} nanoparticles are well-dispersed and in the size of 10–50 nm. -- Abstract: High quality and dispersible rare-earth oxides (RE{sub 2}O{sub 3}) nanocrystals have drawn great attention because of their potential applications in the optical, electrical and biological fields. Here, we demonstrated a simple approach for the production of gadolinium oxide (Gd{sub 2}O{sub 3}) nanoparticles onto the surface of reduced graphene oxide (RGO) sheets by the chemical and the subsequent thermal reduction reactions. The residual oxygen functionalities derived from the reduction of graphene oxide (GO) played an important role to complex Gd{sub 2}O{sub 3} nanoparticles with RGO sheets. And the as-synthesized Gd{sub 2}O{sub 3} nanoparticles are uniform and well-dispersed with their particle size in the range of 10–50 nm. The approach would open up a new window for simple and effective synthesis of high quality RE{sub 2}O{sub 3} in nano scale.