LaMnO_(3)(La_(0.8)Sr_(0.2)MnO_(3))Perovskites for Lean Methane Combustion:Effect of Synthesis Method

The effect of the preparation method on the properties of LaMnO3 and La0.8Sr0.2MnO3 perovskite was studied. Materials were prepared by four methods: sol-gel, chemical combustion, solvothermal and spray pyrolysis and characterized. The effect of the synthesis method on the texture, acid-base character of the surface, reducibility with hydrogen, oxygen desorption, surface composition and catalytic activity for combustion of lean methane was studied. It was found that synthesis method affects physicochemical properties of obtained materials-solvothermally produced materials exhibit well-developed surface area, presence of reactive oxygen species on surface and high catalytic activity for CH4 combustion. Generally, LaMnO3 and La0.8Sr0.2MnO3 perovskites show catalytic activity for lean CH4 combustion comparable or higher than the activity of 0.5 wt.% Pt/Al2O3 but lower than 1 wt.% Pd/Al2O3.

Synthesis,structure and NIR luminescence properties of Yb^3+ and Bi^3+-activated vanadate GdVO4

Near-infrared emission of Yb3＋ and Bi3＋-co-doped GdVO4 vanadate phosphors obtained via the modified Pechini＇s method was reported. The phase purity and structure of samples were characterized by X-ray powder diN＇action （XRD）, X-ray energy disper- sion spectroscopy （EDS）, scanning electron microscopy （SEM）, Raman and infrared （IR） spectroscopy. Photoluminescence emission （PL） and excitation （PLE） spectra were recorded and investigated in details. Results indicated that upon near-UV excitation （340 nm） in the （Bi3＋-V5＋） charge transfer state this phosphor had a strong broad band yellow-green emission （3Pi--ISo） of Bi3＋ ions and also NIR emission （2Fs/2-2Fv/2） of Yb3＋ ions in the range of 950-1050 nm, which matched well with the spectral response of the sili- con-based solar cells. The decreasing Bi3＋ emission with increasing Yb3＋ concentration proved the occurrence of energy transfer from Bi3＋ to Yb3＋ ions. Results demonstrated that Yb3＋ and Bi3＋-co-doped GdVO4 vanadate phosphors might act as a NIR down-conversion （DC） solar spectral converter to enhance the efficiency of the silicon-based solar cells.

Laser-induced white-light emission from graphene ceramics–opening a band gap in graphene

Recent theoretical and experimental studies have indicated the existence of a new stable phase of carbon with mixed sp^(2) and sp^(3) hybridized bonds—diaphite.Such a two-layered structure with sp^(2)/sp^(3) bonds may be observed after the photostimulation of highly oriented pyrolytic graphene with femtosecond laser pulses.This hidden multistability of graphene may be used to create a semiconducting phase immersed in the semimetallic continuum,resulting in bandgap opening.We demonstrate that bandgap opening and light emission from graphene is possible using continuous-wave laser beams with wavelengths from the visible(405 nm)to the near-infrared range(975 nm).We demonstrate that without the application of cooling,the effective temperature of the emitting sample remains lower than 900 K,which is far below the value predicted by the theory of black-body radiation.Moreover,light emission from a graphene sample may be observed at temperatures as low as 10 K.

Zirconium metal organic framework for design of tetragonal rare earth-doped zirconia nanoparticles

Zirconium metal-organic frameworks ZrOBDC(where BDC=C6H4(COOH)2,terephthalic acid)doped and co-doped with rare earth ions Ln(ZrOBDC:Ln^3+,where Ln^3+=Eu3+and Tb^3+as well as Er^3+and Yb^3+)were used as precursors for the design of tetragonal rare earth doped zirconia nanoparticles(t-ZrO2:Ln^3+NPs)through annealing process.Preparation,characterization and luminescence properties of ZrOBDC:Ln^3+and ZrO2:Ln^3+NPs were investigated.The as-obtained t-ZrO2:Ln^3+NPs have high purity with an average size of 20-30 nm.The luminescence spectra of ZrOBDC:Tb^3+and ZrOBDC:Eu3+display strong green and red emission at around 544 and 611 nm which correspond to 5D4→7F5 and 5D0→7F2 transitions of Tb^3+and Eu3+ions,respectively.The green and red up-conversion emissions of ZrO2:Er^3+,Yb^3+NPs due to 2H11/2,4S3/2→4I15/2 and 4F9/2→4I15/2 transitions of the Er^3+ions are observed under 976 nm laser excitation.