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The adsorption of Au (n = 1-4) clusters on perfect and defective MoS monolayers is studied using density functional theory. For the pristine MoS monolayer, our results show that the electrons are transferred from the support to the adsorbed Au clusters, thus a p-doping effect is achieved in the pristine MoS monolayer by the Au cluster adsorption, which is in good agreement with the experimental findings. The adsorption of Au clusters can introduce mid-gap states, which modify the electronic and magnetic properties of the systems. The adsorbates containing an odd number of Au atoms can introduce a spin magnetic moment of 1 μ into the perfect MoS monolayer, while those systems containing an even number of Au atoms are spin-unpolarized. Two categories of defects, i.e., a single S vacancy and Mo antisite defect with one Mo atom replacing one S atom, are considered for the defective monolayer MoS. Compared with the pristine MoS monolayer, the adsorption energies for Au clusters are significantly increased for the MoS monolayer with a single S vacancy, and there are more electrons transferred from the MoS monolayer with an S vacancy to the Au clusters. The mid-gap states and odd-even oscillation magnetic behavior can also be observed when Au clusters are adsorbed on the MoS monolayer with an S vacancy. For those systems of Au clusters on MoS monolayers with Mo antisite defects, the adsorption energies as well as the magnitude and the direction of transferred charge are similar to those for the MoS monolayer with an S vacancy. The spin-polarizations appear in all systems with Mo antisite defects. Our investigations suggest that the electronic and magnetic properties of MoS nanosheets can be effectively modulated by the adsorption of Au clusters.

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aMotivated by the recent realization of two-dimensional (2D) nanomaterials as gas sensors, we have investigated the adsorption of gas molecules (SO 2 , NO 2 , HCN, NH 3 , H 2 S, CO, NO, O 2 , H 2 , CO 2 , and H 2 O) on the graphitic GaN sheet (PL-GaN) using density functional theory calculations. It is found that among these gases, only SO 2 and NH 3 gas molecules are chemisorbed on the PL-GaN sheet with apparent charge transfer and reasonable adsorption energies. The electronic properties (especially the electric conductivity) of the PL-GaN sheet showed dramatic changes after the adsorption of NH 3 and SO 2 molecules. However, the strong adsorption of SO 2 on the PL-GaN sheet makes desorption difficult, which precludes its application to SO 2 sensors. Therefore, the PL-GaN sheet should be a highly sensitive and selective NH 3 sensor with short recovery time. Furthermore, the adsorption of NO (or NO 2 ) molecules introduces spin polarization in the PL-GaN sheet with a magnetic moment of about 1 m B , indicating that magnetic properties of the PL-GaN sheet are changed obviously. Based on the change of magnetic properties of the PL-GaN sheet before and after molecule adsorption, the PL-GaN sheet could be used as a highly selective magnetic gas sensor for NO and NO 2 detection.

Ce 3+ -doped Ba 2 Ln(BO 3 ) 2 Cl (Ln ¼ Gd, Y) phosphors were synthesized through a conventional hightemperature solid state method in CO atmosphere. Structural and spectroscopic characterizations of the samples have been performed by X-ray diffraction and photoluminescence spectra measurements. The phosphors can be efficiently excited by near ultraviolet (n-UV) light resulting in blue emission. The optimal Ce 3+ dopant concentrations in both compounds were determined, and the concentration quenching mechanisms were also discussed. The photoluminescence excitation (PLE) and emission (PL) spectra, and decay curves at liquid helium temperature were measured to analyze the crystallographic occupancy sites of Ce 3+ in the Ba 2 Ln(BO 3 ) 2 Cl (Ln ¼ Gd, Y) hosts. The thermal stabilities of the phosphors Ba 2 Ln(BO 3 ) 2 Cl:Ce 3+ (Ln ¼ Gd, Y) were studied using the dependence of the luminescence intensities on temperature (300-500 K), and their luminescence quenching temperatures and thermal activation energies were also determined. The results indicate that the phosphor Ba 2 Gd(BO 3 ) 2 Cl:Ce 3+ offers excellent optical properties as a potential blue-emitting phosphor candidate for n-UV LEDs, such as a higher thermal stability and a stronger luminescence intensity, than those of the phosphor Ba 2 Y(BO 3 ) 2 Cl:Ce 3+ .

Eu3+-activated layered perovskite ionic conductor KGdTiO4 red emitting phosphors to be used for ultraviolet based light emitting diodes (LEDs) and field emission displays (FEDs) were successfully synthesized by a modified sol–gel method.

Properties of gas molecules (NO, NH 3 , and NO 2 ) adsorbed on two-dimensional GaN with a tetragonal structure (T-GaN) are studied using first-principles methods. Adsorption energy, adsorption distance, Hirshfeld charge, electronic properties, electric conductivity, and recovery time are calculated. It is found that these three molecules are all chemisorbed on the T-GaN with reasonable adsorption energies and apparent charge transfer. The electronic properties of the T-GaN present dramatic changes after the adsorption of NO 2 and NO molecules, especially its electric conductivity, but NH 3 molecule hardly changes the electronic properties of the T-GaN. Furthermore, the recovery time of the T-GaN sensor at T = 300 K is estimated to be quite short for NO 2 and NO but very long for NH 3 . Moreover, the magnetic properties of the T-GaN are changed obviously due to the adsorption of NO (or NO 2 ) molecule. Therefore, we suggest that the T-GaN can be a prominent candidate for application as NO 2 and NO molecule sensors.

Among MoS2/MX2 heterobilayers only the MoS2/WSe2 system exhibits a direct bandgap, and strain can be used to tune the direct bandgap character of the MoS2/MoSe2 and MoS2/WSe2 heterobilayers.