The electronic and optical properties of hexagonal wurtzite AlN doped with Zn and Mg are studied based on the density functional theory. The density of states, dielectric function and absorption spectra are calculated using plane-wave ultrasoft pseudo-potential and the generalized gradient approximation (GGA). The absorption peaks are found during 0-13 eV and 43-48 eV in Mg doped AlN, while in Zn doped AlN, only during 0-15eV. The absorption peak about 43-48 eV found in Mg doped AlN is due to the transition of the deep 2p energy level in Mg to conduction band. The first peak of the dielectric imaginary part is related to the transition of the doped atoms. The peak of the dielectric imaginary part and absorption peak appears about 8 eV is due to the transition of N 2p to Al 3p state. Results show that the electronic and the optical properties of hexagonal wurtzite AlN are directly related to the electronic structure of the impurities in the crystal.

Thermal conductivity of aluminum nitride (AlN) has been calculated by density functional perturbation theory (DFPT) and quasi-harmonic approximation (QHA) combined with Debye theory in the paper. Debye temperature is evaluated respectively from sound velocity and heat capacity. From 300K up to 1000K, the predicted thermal properties in pure crystal AlN based on these two Debye temperatures are compared with each other and the latter shows excellent agreement with Slack’s experimental data. The relative difference based on Debye temperature from heat capacity is within the limits of ±5.5%. This agreement with experiment is due to the Debye temperature derived from capacity contains the temperature effect while describe the three phonon process.

The effects of grain sizes and oxygen impurities on thermal conductivity in aluminum nitride (AlN) ceramics has been calculated by density functional perturbation theory (DFPT) and quasi-harmonic approximation (QHA) combined with Debye theory in the paper. From 300K up to 1000K, the predicted thermal properties are compared with experimental data. The agreements with experiment suggest that the theoretical method used in the paper is an effective approach. From our theoretical study, the reduction of thermal conductivity is greater between grain sizes of 1μm and 5μm, while it’s smaller between 8μm and 10μm. Oxygen defects bring about greater influence on thermal conductivity at low temperature than at high temperature. The influence of the oxygen defect is not as significant as the grain sizes when the oxygen concentrations are less than 0.70 at. %, so it’s more important to increase the grain sizes than reduce the oxygen contents in the preparation process to achieve high thermal conductivity AlN ceramics.

Thermal management is one of the major challenges in the development of high powered LEDs. The effects on thermal conductivity of impurity concentration and thickness are studied in Cu doped AlN (AlN:Cu) phosphor in the paper. Density functional perturbation theory (DFPT) and quasi-harmonic approximation (QHA) combined with Debye model are used in the calculation. The results show that thermal conductivity of AlN:Cu is higher than that of Nd doped ytterbium aluminum garnet (YAG:Nd) from 300K up to 1000K thus the temperature of LEDs can be controlled efficiently. Thermal conductivity increases with the rising of thickness while it decreases with the addition of Cu concentration. The influence of Cu concentration on thermal conductivity depends on temperature. The lower the temperature is, the bigger the influence.

A novel sol-gel hybrid material was synthesized based on sol-gel method using TEOS as precursors, KH570 as modifying agent, and EGDMA as cross linking agent. The obtained hybrid material exhibited excellent affinity to clenbuterol and florfenicol, and successfully applied to the home-made miniaturized SPE device for extraction and clean-up of clenbuterol and florfenicol from milk samples. Under the optimized conditions, the consumption of the hybrid material as SPE sorbent was low to 20 mg. Satisfactory linearity ranging from 0.2-20 μg/mL were obtained with r20.9990, and the recoveries at three spiked levels were ranged from 90.7-103.7% with RSD less than 2.7%.