A series of（90–x）Li2B4O7-10Nb2O5-xNd2O3 glass samples（x=0, 5 mol.%, 10 mol.%, 15 mol.%, 20 mol.% and 25 mol.%） were synthesized using melt quenching technique. X-ray diffraction（XRD）, differential thermal analy...A series of（90–x）Li2B4O7-10Nb2O5-xNd2O3 glass samples（x=0, 5 mol.%, 10 mol.%, 15 mol.%, 20 mol.% and 25 mol.%） were synthesized using melt quenching technique. X-ray diffraction（XRD）, differential thermal analyzer（DTA）, Fourier transformed infrared（FTIR）, ultraviolet-visible-near-infrared（UV-Vis-NIR） spectrometer and photoluminescence（PL） spectroscopic characterizations were made to examine the influence of Nd3＋ concentration on the physical, structural and optical properties. Various physical properties such as glasses density, molar volume, thermal stability, ion concentration, polar on radius, inter-nuclear distance, field strength, cut-off wavelength, energy band gap and Urbach energy were calculated. The samples were amorphous in nature and confirmed from XRD pattern. The FTIR spectra revealed the presence of BO3 and BO4 functional groups. UV-Vis-NIR spectra exhibited nine prominent bands centered at 353, 430, 475, 524, 583, 681, 745, 803, 875 nm corresponding to the transitions from the ground state to ^4D（3/2）, ^2P（1/2）, ^2G（9/2）, ^4G（7/2）, ^4G（5/2）, ^4F（9/2）, ^4F（7/2）, ^4F（5/2）, ^4F（3/2） excited states, respectively. Moreover, the emission spectra at 355 nm excitation displayed three peaks centered at 903 nm（^4F（3/2）→^4I（9/2））, 1059 nm（^4F（3/2）→^4I（11/2）） and 1333 nm（^4F（3/2）→^4I（13/2））, respectively. Fluorescence lifetime was recorded between 53.69 to 28.43 μs. It was found that varying concentration of Nd^（3＋） ions strongly affected the physical, structural and optical properties of the glass samples.展开更多
Electronic and optical properties of small silicon quantum dots having 3 to 44 atoms per dot with and without surface passivation are investigated by computer simulation using the pseudo-potential approach.An empirica...Electronic and optical properties of small silicon quantum dots having 3 to 44 atoms per dot with and without surface passivation are investigated by computer simulation using the pseudo-potential approach.An empirical pseudo-potential Hamiltonian,a plane-wave basis expansion and a basic tetrahedral structure with undistorted local bonding configurations are used.The structures of the quantum dots are relaxed and optimized before and after hydrogen passivation.It is found that the gap increases more for a hydrogenated surface than the unpassivated one.Thus,both quantum confinement and surface passivation determine the optical and electronic properties of Si quantum dots.Visible luminescence is probably due to the radiative recombination of electrons and holes in the quantum-confined nanostructures.The effect of passivation of the surface dangling bonds by hydrogen atoms and the role of surface states on the gap energy is also examined.The results for the density of states,the dielectric function,the frequency dependent optical absorption cross section,the extinction coefficient and the static dielectric constants of the size are presented.The importance of the confinement and the role of surface passivation on the optical effects are discussed.展开更多
基金Project supported by the Ministry of Higher Education(Malaysia)(4F412)Postgraduate Fellowship Universiti Teknologi Malaysia(UTM)
文摘A series of（90–x）Li2B4O7-10Nb2O5-xNd2O3 glass samples（x=0, 5 mol.%, 10 mol.%, 15 mol.%, 20 mol.% and 25 mol.%） were synthesized using melt quenching technique. X-ray diffraction（XRD）, differential thermal analyzer（DTA）, Fourier transformed infrared（FTIR）, ultraviolet-visible-near-infrared（UV-Vis-NIR） spectrometer and photoluminescence（PL） spectroscopic characterizations were made to examine the influence of Nd3＋ concentration on the physical, structural and optical properties. Various physical properties such as glasses density, molar volume, thermal stability, ion concentration, polar on radius, inter-nuclear distance, field strength, cut-off wavelength, energy band gap and Urbach energy were calculated. The samples were amorphous in nature and confirmed from XRD pattern. The FTIR spectra revealed the presence of BO3 and BO4 functional groups. UV-Vis-NIR spectra exhibited nine prominent bands centered at 353, 430, 475, 524, 583, 681, 745, 803, 875 nm corresponding to the transitions from the ground state to ^4D（3/2）, ^2P（1/2）, ^2G（9/2）, ^4G（7/2）, ^4G（5/2）, ^4F（9/2）, ^4F（7/2）, ^4F（5/2）, ^4F（3/2） excited states, respectively. Moreover, the emission spectra at 355 nm excitation displayed three peaks centered at 903 nm（^4F（3/2）→^4I（9/2））, 1059 nm（^4F（3/2）→^4I（11/2）） and 1333 nm（^4F（3/2）→^4I（13/2））, respectively. Fluorescence lifetime was recorded between 53.69 to 28.43 μs. It was found that varying concentration of Nd^（3＋） ions strongly affected the physical, structural and optical properties of the glass samples.
基金by the RMC,UTM under Grant Nos 4D005/RMC and Q.J130000.7126.00J39/GUP.
文摘Electronic and optical properties of small silicon quantum dots having 3 to 44 atoms per dot with and without surface passivation are investigated by computer simulation using the pseudo-potential approach.An empirical pseudo-potential Hamiltonian,a plane-wave basis expansion and a basic tetrahedral structure with undistorted local bonding configurations are used.The structures of the quantum dots are relaxed and optimized before and after hydrogen passivation.It is found that the gap increases more for a hydrogenated surface than the unpassivated one.Thus,both quantum confinement and surface passivation determine the optical and electronic properties of Si quantum dots.Visible luminescence is probably due to the radiative recombination of electrons and holes in the quantum-confined nanostructures.The effect of passivation of the surface dangling bonds by hydrogen atoms and the role of surface states on the gap energy is also examined.The results for the density of states,the dielectric function,the frequency dependent optical absorption cross section,the extinction coefficient and the static dielectric constants of the size are presented.The importance of the confinement and the role of surface passivation on the optical effects are discussed.
