A new YVO4-Nd∶YVO4 composite crystal was grown by a modified Cz method, a 0.10%~0.25%(atomic ratio) concentration gradient doping of Nd3+ in the middle part of the crystal was achieved. In the crystal, the weak absorption coefficient of the Nd3+ doped region is larger than that of the un-doped region, indicating the interface absorption phenomenon. By observing the absorption of the pump light by the composite crystal and temperature distribution in the crystal, it is found that the pumping absorption of the crystal along the axial direction is relatively uniform, and the temperature gradient in the crystal is relatively small. The uncoated composite crystal samples achieve well performance of CW laser at 1 064 nm, with a light-to-light conversion efficiency of 37.0% and a slope efficiency of 40.9%.

With the help of CASTEP first-principles calculations, the different doping structures and thermal properties of the semiconductor AlxGa1-xN were carefully studied for better understanding the influence of the microstructure on the thermodynamic properties in group Ⅲ nitrides, and then provide data support during the design processes of ultra-high power devices. After the optimization of AlxGa1-xN structures, with the increase of Al composition (atomic fraction), the lattice constant, average bond length and lattice heat capacity linearly decreases. The calculation of properties results indicate that the introduction of Al component in GaN will introduce an impurity mode in the frequency band gap. As the concentration of Al component increases, the impurity mode widens and enters the low frequency range. The top frequency of the low frequency band increases with the increase of Al composition, and the top frequency of the low frequency band above 12.5% is larger than (1/2)A1(LO). From 300 K to 700 K, at the fixed temperature, with the increase of Al composition, the heat capacity of AlxGa1-xN alloy linearly decreases. The result in this paper provides a useful reference for the design of Ⅲ-nitride semiconductor high-power devices, such as AlxGa1-xN.

In this paper, β-Ga2O3 films grown preferentially along (403) were prepared on p-type 4H-SiC substrate by pulsed laser deposition (PLD). The results show that the growth temperature has an important influence on the morphology, structure, composition and growth mechanism of β-Ga2O3 film. When the growth temperature increases from 300 ℃ to 500 ℃, the crystalline quality of the β-Ga2O3 film raises with the increasing temperature, but when the temperature further increases to 600 ℃, the crystalline quality of the thin film becomes worse. It was tried to explain that the kinetic energy of atoms deposited on the substrate increases with the increase of growth temperature below 500 ℃, leading to easier migration of atoms, finally, the film is grown in two-dimensional mode and has smaller roughness as measured by AFM. However, when the temperature further increases to 600 ℃, the two-dimensional growth mode is changed to three-dimensional island shape, because of the difference in thermal expansion coefficient between 4H-SiC substrate and β-Ga2O3 thin film, resulted in the larger roughness. The photovoltaic conversion efficiency of heterojunction solar cell based on p-4H-SiC/n-β-Ga2O3 reaches 3.43% under standard test conditions.

The indium and aluminum droplets were simultaneously grown on GaAs (001) substrate by droplet epitaxy method. The morphology of the samples with different indium and aluminum components was characterized by atomic force microscopy (AFM), and the distribution of elements on the surface was observed by XPS and scanning electron microscope (SEM). Results show that the density of InAlAs nanostructures on the surface of mixed deposition decreases with the decreases of indium composition, while the size of individual nanostructures increases. The experimental results show that the density of surface InAlAs nanostructures after hybrid deposition decreases with indium component decreasing, while the size of individual nanostructures becomes larger. SEM and XPS test results prove that the indium on the surface is not all segregated due to the high substrate temperature. It is speculated from the experimental results that when indium & aluminum droplets are deposited on the surface, a mixed indium & aluminum droplet is formed. The formation of dips in the center of the nanostructures formed after complete crystallization of the droplets is mainly due to the downward etching of droplets.

For the growth of AlN crystal by PVT method in nitrogen environment, the growth rate is different due to the different surface chemical properties between Al-polar and N-polar. And differentiated growth behaviors were observed within these surfaces due to the disparate migration behaviors of atoms. AlN growth on Al and N surfaces were carried out under the same conditions, i.e., growth temperature, thermal gradients, pressure, seeds and in the same apparatus. With the purpose of evidently exhibiting the discrepancy of Al and N surfaces, an Al-N growth within one growth cycle was realized by turning half of the seed crystal. For the Al-polar growth, domain boundaries merely within the well-grown planes were found. While for the growth on N surface, morphologies with well-aligned steps were observed, and grain boundaries are covered by these steps at the secondary growth.The growth step of Al surface is smooth but obstructed by defects, and the domain development is obviously independent of each domain growth which were further observed by AFM. The growth step of N surface is not regular but more continuous than that of Al surface, and the continuous growth step (or step cluster) also appears at the original boundary of crystal domain. Consisted with the XRD results, it can be figured out that, N growth is an effective approach to obtain an improved crystalline quality for AlN seeds with lower crystallinity.

The Ce3+ doped CsPbBr3 nanocrystals were prepared by hot-injection method, the crystal phase structure, micro-morphology, chemical composition, light absorption performance, luminescence performance, fluorescence lifetime and optical efficiency of luminescent solar concentrators (LSC) devices were characterized by XRD, TEM, XPS, UV-Vis, PL, Time-resolved fluorescence spectroscopy and J-V curve test. The experimental results show that the cubic phase Ce3+-doped CsPbBr3 nanocrystals with good dispersion and average grain size of 12.26 nm are successfully prepared by hot-injection method. The optical band gap and fluorescence emission peak intensity of Ce3+ doped CsPbBr3 nanocrystals shows a trend of increasing and then decreasing with the increase of Ce/Pb molar ratio. When n(Ce)/n(Pb)=0.25, the optical band gap reaches a maximum of 2.416 eV, the luminescence intensity is the strongest, and the fluorescence emission peak blue-shifts from 515 nm to 510 nm for pure CsPbBr3 nanocrystals. The luminescence performance and stability of Ce3+ doped CsPbBr3 nanocrystals are enhanced. The optical efficiency ηopt of Ce3+ doped CsPbBr3 nanocrystals with polystyrene solution for the preparation of composite thin-film LSC is up to 6.81%.

The structural characteristic and elastic property of ReB2 in P63/mmc structure (hP6-ReB2) were computed using the pseudopotential plane-wave methods based on the density functional theory. The equilibrium structural parameters of hP6-ReB2 were calculated and its stability was verified thermodynamically, dynamically, and mechanically. It is found that the elastic constants, aggregate moduli increase as the pressure increases, and the Poisson ratio σ of hP6-ReB2structure shows its brittleness, and the elastic waves reveals its elastic anisotropy. In addition, the obtained Vickers hardness of hP6-ReB2 is 38.2 GPa. The density of electronic states reveals that there is a strong covalent bond between Re-B and B-B of hP6-ReB2, and the covalent bond increases gradually with the increase of pressure.

In order to study the effect of Na+ doping on the luminescence of Ca2GdNbO6∶0.03Sm3+ phosphors, a series of Ca2GdNbO6∶0.03Sm3+, xNa+ (x=0.01, 0.03, 0.05, 0.07, 0.10; x is mole fraction) phosphors were successfully synthesized by high-temperature solid-state reaction. XRD patterns and the corresponding refinement results show that Na+ were successfully doped into Ca2GdNbO6∶0.03Sm3+ lattices. The luminescent properties of Ca2GdNbO6∶0.03Sm3+, xNa+ phosphors illustrate that the introduction of Na+ effectively improves the luminous intensity of Ca2GdNbO6∶0.03Sm3+ phosphors. Under the 406 nm excitation, the optimum doped concentration of Na+ is 5%, as well as the phosphors emit orange-red light with the strongest emission peak at 602 nm (4G5/2→6H7/2). The calculation of the concentration quenching and the thermal stability of Ca2GdNbO6∶0.03Sm3+, 0.05 Na+ host show that the energy transfer in the matrix occurs mainly among the nearest neighbor ions, and the thermal activation energy is 0.119 eV. The calculated color coordinate (0.593 5, 0.404 7) of the phosphors is located in the orange-red region, which is close to the standard (0.666, 0.333) specified by the international commission on illumination, indicating Ca2GdNbO6∶0.03Sm3+, xNa+ phosphors have potential application prospects in the field of white LEDs.

A series of Eu3+ doped and Li+, Eu3+ co-doped Gd2ZnTiO6 (GZT) red-emitting phosphors were successfully prepared by sol-gel method. The effects of Li+ and Eu3+ ions doping on the crystal structure, microstructure and luminescent properties of the samples were studied. Results show that the obtained double perovskite Gd2ZnTiO 6∶Li+,Eu3+(GZT∶Li+,Eu3+) phosphors crystallized in the monoclinic space group P21/n and are composed of irregular particles with the size of 10 μm. Under the excitation of 395 nm near ultraviolet light, the emission spectrum of GZT∶Eu3+ shows a typical linear characteristic spectrum of Eu3+ ions. The center position of the emission peak is located at 615 nm, which belongs to the 5D0→7F2 transition of Eu3+. The optimum doping concentration of Eu3+ is 0.07 (mole fraction). The obtained samples show obvious concentration quenching effect, and its mechanism can be identified as the electric dipole-dipole interactions(d-d). In addition, it is also found that Li+ doping has no effect on the crystal structure and micro morphology of the samples, but a certain amount of Li+ doping can significantly enhance the fluorescence intensity of the samples. When the concentration of Li+ is 0.05, the intensity of the main emission peak of the phosphor is the largest, which is 4.3 times of the original, indicating that high brightness GZT red-emitting phosphor can be obtained by co-doping Li+ and Eu3+. The CIE color coordinates of GZT∶0.14Eu3+,0.05Li+ phosphor is located at (0.631 1,0.375 3) close to the standard red color coordinates (0.670, 0.330), which is a potential red-emitting phosphor for LED.