Europium-doped gallium nitride (Eu:GaN) nanocrystals with hexagonal wurtzite structures were prepared from the decomposition of the EuxGa1−x(H2NCONH2)6Cl3 precursor at a mild temperature of 350 °C. The absorption spectrum, the excitation spectra and the fluorescence emission spectra of Eu:GaN nanocrystals are measured and discussed. Eu:GaN has a strong fluorescence emission band in the visible region. Furthermore, the first-principles density functional theory has been adopted to explore the fluorescence mechanism. The results show that energy transfer should occur between the GaN host and Eu3+ ions under excitation at 370 nm, and thus the fluorescence emission efficiency of the Eu3+ ions can be improved. In order to further reduce the loss of fluorescence emission and increase the fluorescence quantum yield, Eu:GaN nanocrystals coated by biocompatible silica and dispersed in ethanol are also discussed.

•GNR network is a suitable carrier for supporting alloy nanoparticles dispersedly.•PtAu/GNR has superior catalytic activity for ethanol oxidation.•Anti-CO poisoning capability is analyzed successfully by DFT simulation.•Carbon material support and PtAu co-existence enhance anti-CO poisoning capability.The composited catalyst of graphene nanoribbons supported platinum-gold nanoalloy (PtAu/GNR) was prepared by microwave-assisted polyol method. GNRs network is a suitable carrier to support metal nanoparticles dispersedly. The effects of new GNR support and PtAu co-existence on the electrocatalytic performance of composite catalyst for ethanol oxidation are discussed. For further analyzing the anti-CO poisoning capability, the electron density difference and the electrostatic potential of catalyst surface, and the energy curve of CO oxidation reaction are calculated theoretically based on the first principle. The results show that PtAu/GNR has much superior catalytic activity and higher poisoning tolerance than the monometal composite catalyst.Graphene nanoribbon network is a suitable carrier for supporting PtAu nanoalloy particles dispersedly. PtAu/GNR composite has a high catalytic activity for ethanol oxidation. Density functional theory simulation shows carbon material support and PtAu co-existence can enhance anti-CO poisoning capability. First principle theoretical study provides a way to find and develop better electrocatalysts.

•Strongest CO tolerance results in the best catalytic effect of Pt0.46Pd0.54/GNRs.•PtPd alloy nanoparticles with different Pd concentrations were supported on GNRs.•DFT calculation is used successfully to study CO anti-poisoning ability of catalysts.•Catalyst with PtPd ratio of 0.46:0.54 is found to possess excellent catalytic effect.Graphene nanoribbons decorated with noble metal nanoparticles possess great catalytic performance for ethanol oxidation in direct ethanol fuel cells. Herein, PtPd alloy catalysts supported on graphene nanoribbons are researched, and an appropriate Pt–Pd component with the mole ratios of 0.46:0.54 is found to possess excellent catalytic activity and durability. Moreover, the density functional theory analysis shows that the composite catalyst with Pt:Pd ratio of 1:1 owns the highest negative electronic property and the high adsorption energy to restrict CO adsorption. The great CO anti-poisoning ability may be the main reason for the excellent catalytic performance of Pt0.46Pd0.54/GNRs catalyst.DFT theoretical calculation and electrochemical measurement indicate that the strong CO anti-poisoning ability results in the high catalytic activity and durability of PtPd/GNRs alloy nanocatalysts in DEFC.

•A sizeable single BTG crystal with high quality was grown by Czochraski method.•GeO2 volatilization and melt supercooling are main inducement of inclusion defect.•Accurate refractive indexes of BTG crystal were measured by self-collimating method.•With the giant nonlinear-optical effect, BTG crystal has a good application prospect.Ba2TiGe2O8 (BTG) shows excellent second-order nonlinearity and electro-optical effects. However, it is difficult to grow a perfect BTG single crystal, and the accurate refractive indexes of this crystal are unavailable at present. In this paper, a sizeable single BTG crystal with high quality was grown by Czochraski (CZ) method. SEM and EDS analyses of crystal defect indicate that the volatilization of GeO2 and the obvious supercooling feature of BTG melt were the main inducements of inclusion defects. The accurate refractive indexes were measured by the self-collimating method. The birefringence and SHG results show that the angle phase matching of SHG at 1064 nm hardly be achieved in this crystal. Nevertheless, the effective frequency-doubled laser output may be achieved by using the technique of periodic polarization reversal for quasi phase matching. In view of the high optical transmittance and the huge nonlinear optical coefficients, BTG crystal may be a good candidate material for nonlinear optical devices and electro-optical devices.A sizeable single BTG crystal with high quality was successfully grown by Czochraski method. GeO2 volatilization and melt supercooling are the main inducement of inclusion defect. Accurate refractive indexes of BTG crystal were measured by self-collimating method. With the giant nonlinear-optical effect, BTG crystal has a good application prospect in nonlinear optical devices and electro-optical devices.

•Ga:GIG crystal has a comparable magneto-optical performance with Ga:YIG crystal.•Annealing can improve optical transmittance and affect saturation magnetization.•Ga:GIG bulk single crystals with good quality were successfully grown by EFG method.•Success of growing GIG by EFG provides a new way to grow incongruent melting crystal.•Tc and Ms of Ga:GIG crystal decrease with increasing of Ga3+-doped concentration.Ga-doped Gd3Fe5O12 (GIG) single-crystals with various doping concentration were successfully grown by the edge-defined film fed growth (EFG) technique. XRD pattern and SEM micrographs confirm that the as-grown crystal is in the single GIG phase with good crystal quality. The success of growing Ga:GIG crystal by using EFG method provide a new way to grow the single crystal of the incongruent melting compound. The magnetic parameters such as the Curie temperature Tc, the saturation magnetization Ms, the magnetic coercivity Hc, the magnetic saturation field Hs, the Faraday rotation angle of as-grown crystals were measured. After as-grown crystal was annealed at 800 °C in oxygen atmosphere, the optical transmittance can be significantly enhanced. The reason for the change of the saturation magnetization Ms before and after annealing is also discussed.Graphical abstractGa:GIG crystal successfully grown by EFG method has a good magneto-optical performance.

•Reaction temperature and KOH concentration are the keys to grow BiFeO3 crystal phase.•Growth mechanism of BiFeO3 is closely related to Bi:Fe molar ratio in solution.•Large BiFeO3 crystal was grown at high KOH concentration and low supersaturation.•Increasing compactedness will reduce surface defect and improve crystal quality.Bismuth ferrite crystal is synthesized by hydrothermal method. The effect of hydrothermal temperature, KOH concentration, supersaturation, cooling rate, and compactedness on the crystal phase and the morphology of product were investigated. The results indicated that BiFeO3 microcrystalline with good quality could been synthesized at 140–240 °C with KOH concentration of 4–14 mol L−1. In addition, it is favorable for improving the crystal quality to reduce the supersaturation and decrease the cooling rate. With the increasing of the compactedness, surface holes and cracks of the as-grown crystals would be reduced. The optimization of hydrothermal condition provides guidance to grow BiFeO3 crystal with a large size and high quality for practical application.