Structure and photoluminescence properties of Er^(3+)-doped TiO_2-SiO_2 powders prepared by sol-gel method

Er3＋-doped TiO2-SiO2 powders are prepared by the sol-gel method, and they are characterized by high resolution transmission electron microscopy （HR-TEM）, X-ray diffraction （XRD） spectra, and Raman spectra of the samples. It is shown that the TiO2 nanocrystals are surrounded by an SiO2 glass matrix. The photoluminescence （PL） spectra are recorded at room temperature. A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm. The intensity of the emission, which is related to the defect states, is strongest at the annealing temperature of 800℃. The PL intensity of Er3＋ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO2 particles and Er3＋ ions.

Theoretical Calculations for Structural, Elastic and Thermodynamic Properties of γTiAl Under High Pressure

We investigate the structural and elastic properties of γ TiAl under high pressures using the norm-conservingpseudopotentials within the local density approximation(LDA)in the frame of density functional theory.The calculatedpressure dependence of the elastic constants is in excellent agreement with the experimental results.The elastic constantsand anisotropy as a function of applied pressure are presented.Through the quasi-harmonic Debye model,we alsoinvestigate the thermodynamic properties of γ TiAl.

First-principles study of mechanical stability and thermal properties of MNNi_3 (M=Zn,Mg,Al) under pressure

The mechanical stability,elastic,and thermodynamic properties of the anti-perovskite superconductors MNNi 3（M=Zn,Mg,Al） are investigated by means of the first-principles calculations.The calculated structural parameters and elastic properties of MNNi 3 are in good agreement with the experimental and the other theoretical results.From the elastic constants under high pressure,we predict that ZnNNi 3,MgNNi 3,and AlNNi 3 are not stable at the pressures above 61.2 GPa,113.3 GPa,and 122.4 GPa,respectively.By employing the Debye model,the thermodynamic properties,such as the heat capacity and the thermal expansion coefficient,under pressures and at finite temperatures are also obtained successfully.

First-Principles Calculations of Elastic and Thermal Properties of Molybdenum Disilicide

The first-principles plane-wave pseudopotential method using the generalized gradient approximation within the framework of density functional theory is applied to anaylse the equilibrium lattice parameters, six independent elastic constants, bulk moduli, thermal expansions and heat capacities of MoSi2. The quasi-harmonic Debye model, using a set of total energy versus cell volume obtained with the plane-wave pseudopotential method, is applied to the study of the elastic properties, thermodynamic properties and vibrational effects. The calculated zero pressure elastic constants are in overall good agreement with the experimental data. The calculated heat capacities and the thermal expansions agree well with the observed values under ambient conditions and those calculated by others. The results show that the temperature has hardly any effect under high pressure.

Physical properties of hexagonal WN_2 under pressure

A first-principles study on the mechanical stability, elastic and thermodynamic properties of WN2 with P63/mmc and P-6m2 phases are reported using the pseudo potential plane wave method within the generalized gradient approx- imation. The calculated equilibrium parameters are in good agreement with the available theoretical data. A complete elastic tensor and crystal anisotropies of the ultra-incompressible WN2 are determined in the wide pressure range. By the elastic stability criteria, it is predicted that P63/mmc and P-6m2 phases in WN2 are not stable above 175.1 GPa and 170.1 GPa, respectively. Finally, by using the quasiharmonic Debye model, the isothermal and adiabatic bulk modulus, and the heat capacity of WN2 are also successfully obtained.

Phase Transition and Physical Properties of InS

Using the crystal structure prediction method based on particle swarm optimization algorithm, three phases （Pnnm, C2/m and Pm-3m） for InS are predicted. The new phase Pm-3m of InS under high pressure is firstly reported in the work. The structural features and electronic structure under high pressure of InS are fully investigated. We predicted the stable ground-state structure of InS was the Pnnm phase and phase transformation of InS from Pnnm phase to Pm-3m phase is firstly found at the pressure of about 29.5 GPa. According to the calculated enthalpies of InS with four structures in the pressure range from 20 GPa to 45 GPa, we find the C2/m phase is a metastable phase. The calculated band gap value of about 2.08 eV for fnS with Pnnm structure at 0 GPa agrees well with the experimental value. Moreover, the electronic structure suggests that the C2/m and Pm-3m phase are metallic phases.

Effect of the Time-Dependent Atom-Field Couplings on Entanglement

A model containing two two-level atoms and a single-mode cavity is considered, and the effect of the time-dependent atom-field couplings on entanglement between the two atoms is studied. The results indicate that both for one-photon processes and for two-photon processes, the disappearance of the initial entanglement is delayed due to the linear modulation of the atom-field coupling coefficients as compared to the constant coupling model. The delayed time of the disappearance of the initial entanglement for the two-photon processes is much longer than that for the one-photon processes in the case of adiabatic variation.