Wei CHEN
,
Zhaojun LIN
,
Zhanguo WANG
,
Yan XU and Lanying LIN (Lab. of Semicond. Mater. Sci.
,
Institute of Semiconductors
,
Chinese Academy of Sciences
,
Beijing 100083
,
China )
材料科学技术（英文）
CdS nanoparticles were prepared in air and their stability by air annealing was studied. A small change in crystal structure and particle size was observed by air annealing, but a rapid reduction in fluorescence was found. Through investigation, it is revealed that it is the surface change or reconstruction rather than the variation of the size or structure that decreases the fluorescence.The emission of the particles consists with two peaks which are dependent on the excitation energy. The two peaks are considered to be arisen from "two" different sizes of nanoparticles and may be explained in terms of selectively excited photoluminescence. Finally we discuss why the discrete state of nanoparticles are able to be resolved in the photoluminescence excitation spectrum, but could not be differentiated in the absorption spectrum.
关键词:
We CHEN
,
Zhanguo WANG
,
Zhaojun LIN
,
Yan XU and Lanying LIN(Lab. of Semiconductor Materials Sciences
,
Institute of Semiconductors
,
Chinese Academy of Sciences
,
Beijing 100083
,
China)
材料科学技术（英文）
Two obvious emissions are observed from the ZnS clusters encapsulated in zeolite-Y. The emissionaround 355 nm is sharp and weak, locating at the onset of the absorption edge. The bandaround 535 nm is broad. Strong and Stokes-shifted. Both the two emissions shift to blue andtheir intensities firstly increase then decrease as the loading of ZnS in zeolite-Y or clusters sizedecreases. Through investigation, the former is attributed to the excitonic fluorescence, andthe latter to the trapped luminescence from surface States. The cluster size-dependence of theluminescence may be explained qualitatively by considering both the carrier recombination andthe nonradiative recombination rates. Four peaks appearing in the excitation spectra are assignedto the transitions of 1S-1S, 1S-1P, 1S-1D and sudsce state, respectively. The excitation spectraof the clusters do not coincide with their absorption spectra. The states splitted by quantum-sizeconfinement are detected in the excitation spectra, but could not be differentiated in the opticalabsorption spectra due to inhomogeneous broadening. The size-dependence of the excitationspectra is similar to that of the absorption spectra. Both the excitation spectra of excitonicand of trapped emissions are similar, but change in relative intensity and shift in position areobserved.
关键词:
Zhaojun LIN
,
Zhanguo WANG
,
Wei CHEN and Lanying LIN(Lab. of Sendconductor Materials Science
,
Institute of Semiconductors
,
Chinese Academy of Sciences
,
Beijing 100083
,
China)
材料科学技术（英文）
Samples have been prepared at different temperatures by loading I2 molecules into the cages of zeolite 5A, and the measurements of the absorption spectra have been carried out for the prepared samples. It is shown that I2 molecular clusters are formed in the cages of zeolite 5A,and it is also found that moIecuIar clusters which are bonded with intermoIecuIar forces have an important feature, namely, the intermolecular distance in molecular clusters can be changed on different preparing conditions and the blue shift of absorption edges can not be as the criterion of forming molecular clusters.
关键词:
Journal of Applied Physics
High-order perturbation formulas for the electron paramagnetic resonance g factor for a 3d(7) ion in cubic tetrahedral MX4 clusters are established from a cluster approach. In the formulas, not only the conventional contribution from the crystal-field (CF) mechanism, but also the contribution from charge-transfer (CT) (which is often omitted) are considered. Based on the formulas, the g-shifts Deltag (=g-g(s), where g(s)=2.0023) of Co2+ ions in III-V semiconductors GaP, InP, and GaAs are reasonably explained. It is found that the relative importance of the CT mechanism (characterized by Deltag(CT)/Deltag(CF)) increases with increasing covalency and hence with increasing atomic number of the ligand. Therefore, for 3d(n) ions in a strongly covalent crystal, the contributions to the g factor from both CF and CT mechanisms should be taken into account. (C) 2004 American Institute of Physics.
关键词:
atomic screening constants;scf functions;transition;crystal;impurities;spectra;states;epr
Physica B-Condensed Matter
The band structures of the filled tetrahedral semiconductors LiMgN and LiZnN, viewed as the zinc-blende (MgN)(-) and (ZnN)(-) lattices partially filled with He-like Li+ ion interstitials, were studied using the full-potential linearized augmented plane wave method (FP-LAPW) within density functional theory. The conduction band distortions of LiMgN and LiZnN, compared to their "parent" zinc-blende analog AlN and GaN, are discussed. It was found that the insertion of Li+ ions at the interstitial sites near the cation or anion pushes the conduction band minimum of the X point in the Brillouin zone upward, relative to that of the Gamma point, for both (MgN)- and (ZnN)- lattices (the valence band maximum is at Gamma for AlN, GaN, LiMgN, and LiZnN), which provides a method to convert a zinc-blende indirect gap semiconductor into a direct gap material, but the conduction band distortion of the beta phase (Li+ near the cation) is quite stronger than that of the alpha phase (Li+ near the anion). The total energy calculations show the alpha phase to be more stable than the beta phase for both LiMgN and LiZnN. The Li-N and Mg-N bonds exhibit a strong ionic character, whereas the Zn-N bond has a strong covalent character in LiMgN and LiZnN. (C) 2004 Elsevier B.V. All rights reserved.
关键词:
FP-LAPW method;semiconductor;conduction band;direct and indirect band;gap;zinc-blende;thin-films;gap;growth
Journal of Physics-Condensed Matter
The results of a plane-wave pseudopotential study on the mechanical and electronic properties of twelve III-V zinc-blende (ZB) and wurtzite (WZ) semiconductors under pressure are presented. The lattice parameters, bulk moduli B-0, energy band types, band-gaps E-g(Gamma) at the Gamma point, and pressure dependences of E-g(Gamma) are investigated in detail. Our results show that the E-g(Gamma)-P relations can be classified into two distinct types for these ZB and WZ phases. A transformation from one type of E-g(Gamma)-P-relation to the other type is found to occur in some WZ phases. Linear relationships between the bulk moduli and the inverse of unit-cell volumes at P = 0 are also found for the ZB and WZ phases.
关键词:
direct energy-gap;hydrostatic-pressure;electronic-structure;gallium;nitride;dependence;temperature;state;inp;photoluminescence;transitions
