Graphene-ZnO nanocomposites were synthesized successfully through a one-step solvothermal approach. The mor-phology, structure, and composition of the prepared nanocomposites were investigated by scanning electron microscopy （SEM）, transmission electron microscope （TEM）, laser micro Raman spectroscopy, and Fourier transform infra-red spec-troscopy （FT-IR）. The outcomes confirmed that this approach is comparatively steady, practicable, and operable compared with other reported methods. The electrochemical performance of the graphene-ZnO electrodes was analyzed through cyclic voltammetry, altering-current （AC） impedance, and chronopotentiometry tests. The graphene-ZnO electrodes exhib-ited an improved electrode performance with higher specific capacitance （115 F·g^-1 ）, higher electrochemical stability, and higher energy density than the graphene electrodes and most reported graphene-ZnO electrodes. Graphene-ZnO nanocom-posites have a steady reversible charge/discharge behavior, which makes them promising candidates for electrochemical capacitors （ECs）.
A series of K3Gd1-x-y（PO4）2：xCe^3＋, yTb^3＋ phosphors are synthesized by the solid-sate reaction method. X-ray diffraction and photoluminescence spectra are utilized to characterize the structures and luminescence properties of the as-synthesized phosphors. Co-doping of Ce^3＋ enhances the emission intensity of Tb^3＋ greatly through an efficient energy transfer process from Ce^3＋ to Tb^3＋. The energy transfer is confirmed by photoluminescence spectra and decay time curves analysis. The efficiency and mechanism of energy transfer are investigated carefully. Moreover, due to the non- concentration quenching property of K3Tb（PO4）2, the photoluminescence spectra of K3Tb1-x（PO4）2：xCe^3＋ are studied and the results show that when x = 0.11 the strongest Tb^3＋ green emission can be realized.
The upconversion（UC） of the rare earth doped glass-ceramics has been extensively investigated due to their potential applications in many fields, such as color display, high density memories, optical data storage, sensor and energy solar cell, etc. Many series of them, especially the oxyfluorides glasses containing Ba2 LaF 7 nanocrystals were studied in this review work, due to the thermal and mechanical toughness, high optical transmittance from the ultraviolet to the infrared regions, and a low nonlinear refractive index compared to the other commercial laser glasses. Moreover, the energy transfer（ET） between the rare earth ions and transition metals plays an important role in the upconversion process. The cooperative ET has been researched very activly in UC glasses due to applications in the fields of solar cells, such as in the Er/Yb, Tm/Yb, Tb/Yb, Tb/Er/Yb and Tm/Er/Yb couples. The present article reviews on the recent progress made on：（i） upconversion materials with fluoride microcrystals in glasses and the mechanisms involved, including the UC in double and tri-dopant RE ions activated fluoride microcrystal, energy transfer process; and（ii） the effect of the metal Mn and nanoparticles of Au, Ag, Cu on the enhancement of UC emissions. Discussions have also been made on materials, material synthesis, the structural and emission properties of glass-ceramics. Additionally, the conversion efficiency is still a challenge for the spectra conversion materials and application; challenge and future advances have also been demonstrated.
Eu3+-activated red-emitting Ba2Gd2Si4O13 phosphors are prepared via microwave(MW) synthesis and solid-state(SS) method. The structural and luminescent properties of phosphors are investigated by X-ray diffraction(XRD), photoluminescence(PL) spectra and scanning electron microscopy(SEM). Upon 393 nm excitation, compared with the sample sintered by SS method, luminescence enhancement is observed in the sample synthesized by MW method. The mechanism of MW synthesis process is discussed in detail. Results indicate that the PL enhancement is probably related to the concave-convex phosphor surfaces and uniform grains, which may reinforce scattering of excitation light. Our research may further promote the understanding of MW synthesis and extend the application of Eu3+-activated Ba2Gd2Si4O13 in white light-emitting diodes.
KaGd（PO4）2：Tb3＋ phosphors are synthesized by the solid reaction method, and the phases and lu- minescence properties of the obtained phosphors are well characterized. The emission spectra of KaGd（PO4）2：Tb3＋ exhibit the typical emissions of Tb3＋. Concentration quenching of Tb3＋ is not observed in KaGd（PO4）2：Tb3＋, likely because the shortest average distance of Tb3＋-Tb3＋ in KaGd（POn）2：Tb3＋ is adequately long such that energy transfer between Tb3＋-Tb3＋ ions cannot take place effectively. This re- sult indicates that KaTb（P04）2 phosphors have potential application in near ultraviolet （n-UV）-convertible phosphors for white light-emitting diodes.
The Er^3＋/yb^3＋ co-doped transparent oxyfluoride glass-ceramics containing CaF2 nano-crystals were successfully prepared. After heat treatments, transmission electron microscopy （TEM） images showed that CaF2 nano-crystals of 20-30 nm in diameter precipitated uniformly in the glass matrix. luminescence of Er^3＋ at 540 nm and 658 nm was observed in Comparing with the host glass, high efficiency upconversion the glass ceramics under the excitation of 980 nm. Moreover, the size of the precipitated nano-crystals can be controlled by heat-treatment temperature and time. With the increase of the nano-crystal size, the intensity of the red emission increased more rapidly than that of the green emission. The energy transfer process of Er^3＋ and Yb^3＋ was convinced and the possible mechanism of Er^3＋ up-conversion was discussed.
A series of Ba5Si8O（21）：0.02Eu^2＋,0.09RE^3＋ persistent phosphors were synthesized by the solid-state reaction method.The measurement results of photoluminescence（PL）,phosphorescence and thermoluminescence（TL）were analysed and discussed.The XRD results showed that samples codoped with different RE^3＋ were Ba5Si8O（21） single pure phase.Under the excitation,all samples exhibited a broad Eu^2＋ characteristic emission,and the La^3＋ co-doped sample emitted the brightest photoluminescence even though its persistent luminescence property was the worst because of the weakest electronegativity.However,Nd^3＋ electronegativity was suitable,thus after activation,the Ba5Si8O（21）：Eu^2＋,Nd^3＋ sample had the best persistent luminescence performance with the highest phosphorescence intensity and the persistent luminescence decay time beyond 8 h.The Nd^3＋ co-doped sample also had the largest thermoluminescence integral area which proved effectively it had longer persistent luminescence time.The luminescence mechanism was also proposed to study the photoluminescence and persistent luminescence process.These results showed that RE^3＋ electronegativities were distinctly important for persistent phosphors and choosing suitable electronegativity codopant was conducive to enhancing the phosphorescent performance.
The effect of glass network modifier R2O （R=Li, Na, K） on upconversion luminescence in Er3＋/yb3＋ co-doped NaYF4 oxyfluoride glass-ceramics was investigated. NaYF4 nanocrystals with different sizes were studied under glass network modifier alkali mental oxide. The nanocrystals size in NaYF4 of Li2O modified samples was 11 nm, whereas in the Na20 and K2O modified sample, the crystal size was 25 and 43 nm, respectively. It was found that red, yellow and green upconversions were observed in SAL, SAN, SAK glass ceramics. The reported results would deepen the understanding of size effects on the lanthanide upcon- version in nanocrystals.
A novel red-emitting phosphor, CaYA1307： Eu^3＋, Sm^3＋, is synthesized by a combustion method at a low temperature （850 ℃）, and the single phase of CaYA1307 is confirmed by powder X-ray diffraction measurements. The photoluminescence property results reveal that the red emission intensity of Eu^3＋ is strongly dependent on the Sm^3＋ concentration. Only the Eu^3＋ luminescence is detected in the Eu^3＋-Sm^3＋ co-doped CaYA1307 phosphor with 393 nm excitation. However, under the characteristic excitation （402 nm） of Sm^3＋, not only the Sm^3＋ emission but also the Eu^3＋ emission are observed. A possible mechanism of the energy transfer between Sm^3＋ and Eu3＋ is investigated in detail.
A novel white-emitting Ca_2Ga_2GeO_7：Dy^（3＋） phosphor was synthesized via a high-temperature solid-state reaction.The crystal phase was analyzed by X-ray diffraction（XRD）,and the photoluminescence（PL） properties were studied by luminescence spectra and fluorescence decay curves.Under the excitation of 347 nm,the obtained phosphor exhibited strong emission in the blue region peaked at 478 nm,yellow at 574 nm and a weak red emission band at 665 nm,corresponding to the characteristic transitions of ~4F_（9/2）to ~6H_（15/2）,~6H_（13/2） and ~6H_（11/2） of Dy^（3＋）,respectively.By varying the doping concentration of Dy^（3＋）,tunable colors from blue-white to yellow-white were obtained in the phosphors.Besides,by codoping charge compensators（Li~＋,Na~＋,K~＋ and Ga^（3＋）） in Ca_2Ga_2GeO_7：Dy^（3＋）,the optimum CE color coordinate and PL intensity were obtained in Ca_2Ga_2GeO_7：Dy^（3＋）,K~＋.Accordingly,the PL mechanism of Ca_2Ga_2GeO_7：Dy^（3＋） was discussed briefly.
