Pure and Smdoped NdOnanophosphors were synthesized using modified Pechini method. The phase formation with symmetry of the sample is confirmed by the Rietveld refinement of the powder Xray diffraction(PXRD) data. The ...Pure and Smdoped NdOnanophosphors were synthesized using modified Pechini method. The phase formation with symmetry of the sample is confirmed by the Rietveld refinement of the powder Xray diffraction(PXRD) data. The surface morphology and the crystallite size were examined using scanning electron microscopy(SEM) and transmission electron microscopy(TEM) and the results confirmed that the synthesized particles are in nanosize. The energy-dispersive X-ray(EDX) analysis was done to confirm the purity of the sample. The optical properties of the sample were studied using ultraviolet-visible range(UV-Vis) spectroscopic analysis and photoluminescence studies. The calculated band gap of the synthesized NdOwas found to be higher than that of bulk NdO. The photoluminescence(PL) of the prepared samples reveals that doping with Sm3+ ion has influenced the optical properties. Quantitative investigation on charge density distribution was done by analysing the 3-dimensional and 2-dimensional charge density maps drawn along the bonding directions. The maximum entropy method(MEM)/Rietveld analysis was used for the first time to analyse the charge density in the chosen system. Charge density arrangement in the unit cell is correlated to the analysed photoluminescent(PL) properties. The spectral behaviour of the samples has been explained through charge ordering which are verified using experimental data obtained. The studies on these materials have shown that these nanophosphors will provide promising application for near-ultraviolet lightemitting diodes(n-UV-LEDs).展开更多
In this paper we reported the preparation and extensive characterization of La9.83–x Sr x Si6O26＋δ（0≤x≤0.50） precursors, intermediate and final products. The sintering reactions, the phase formation, the struct...In this paper we reported the preparation and extensive characterization of La9.83–x Sr x Si6O26＋δ（0≤x≤0.50） precursors, intermediate and final products. The sintering reactions, the phase formation, the structure as well as the powders＇ morphology were studied by means of thermogravimetric analysis, X-ray diffraction（XRD）, Fourier-transform infrared spectroscopy（FTIR） and scanning electron microscopy（SEM）. Moreover, the effect of stoichiometry on precursor＇s structure and morphology as well as on intermediate and final products was reported. As was concluded pure La9.83Si6O26＋δ, La9.38Sr0.45Si6O26＋δ and La9.33Sr0.50Si6O26＋δ could be prepared after sintering at 1400 °C for 20 h while La9.68Sr0.15Si6O26＋δ and La9.53Sr0.30Si6O26＋δ compounds contained minor traces（〈3.5%） of La2Si2O7 secondary phase. Concerning the synthesis, there have been no previous reports on the preparation of pure La9.83Si6O26＋δ, La9.38Sr0.45Si6O26＋δ and La9.33Sr0.50Si6O26＋δ compounds. The final powders consisted of spherical particles and an increase of Sr content seemed to inhibit sintering phenomena. The existence of interstitial oxygen at intermediate crystallographic positions of apatite structure had great effect on Si O4 sub-structure distortion. The increase of Sr content led to a major reduction of interstitial oxygen quantity and the refutation of silicon tetrahedron distortion.展开更多
文摘Pure and Smdoped NdOnanophosphors were synthesized using modified Pechini method. The phase formation with symmetry of the sample is confirmed by the Rietveld refinement of the powder Xray diffraction(PXRD) data. The surface morphology and the crystallite size were examined using scanning electron microscopy(SEM) and transmission electron microscopy(TEM) and the results confirmed that the synthesized particles are in nanosize. The energy-dispersive X-ray(EDX) analysis was done to confirm the purity of the sample. The optical properties of the sample were studied using ultraviolet-visible range(UV-Vis) spectroscopic analysis and photoluminescence studies. The calculated band gap of the synthesized NdOwas found to be higher than that of bulk NdO. The photoluminescence(PL) of the prepared samples reveals that doping with Sm3+ ion has influenced the optical properties. Quantitative investigation on charge density distribution was done by analysing the 3-dimensional and 2-dimensional charge density maps drawn along the bonding directions. The maximum entropy method(MEM)/Rietveld analysis was used for the first time to analyse the charge density in the chosen system. Charge density arrangement in the unit cell is correlated to the analysed photoluminescent(PL) properties. The spectral behaviour of the samples has been explained through charge ordering which are verified using experimental data obtained. The studies on these materials have shown that these nanophosphors will provide promising application for near-ultraviolet lightemitting diodes(n-UV-LEDs).
基金funded by the Research Committee of National Technical University of Athens
文摘In this paper we reported the preparation and extensive characterization of La9.83–x Sr x Si6O26＋δ（0≤x≤0.50） precursors, intermediate and final products. The sintering reactions, the phase formation, the structure as well as the powders＇ morphology were studied by means of thermogravimetric analysis, X-ray diffraction（XRD）, Fourier-transform infrared spectroscopy（FTIR） and scanning electron microscopy（SEM）. Moreover, the effect of stoichiometry on precursor＇s structure and morphology as well as on intermediate and final products was reported. As was concluded pure La9.83Si6O26＋δ, La9.38Sr0.45Si6O26＋δ and La9.33Sr0.50Si6O26＋δ could be prepared after sintering at 1400 °C for 20 h while La9.68Sr0.15Si6O26＋δ and La9.53Sr0.30Si6O26＋δ compounds contained minor traces（〈3.5%） of La2Si2O7 secondary phase. Concerning the synthesis, there have been no previous reports on the preparation of pure La9.83Si6O26＋δ, La9.38Sr0.45Si6O26＋δ and La9.33Sr0.50Si6O26＋δ compounds. The final powders consisted of spherical particles and an increase of Sr content seemed to inhibit sintering phenomena. The existence of interstitial oxygen at intermediate crystallographic positions of apatite structure had great effect on Si O4 sub-structure distortion. The increase of Sr content led to a major reduction of interstitial oxygen quantity and the refutation of silicon tetrahedron distortion.
