The Preparation And Characteristics Of Organic Small Molecules Beq₂ And BeBq₂ Crystal

Organic small molecules semiconductors are mainly composed of light elements such as C, H, O, and N, which have weaker spin-orbit coupling and longer spin relaxation time than the counterparts of inorganic materials. Organic small molecules semiconductors have been allured much more attentions, because of their novel optoelectronic performances, mechanical flexibility, convenience for preparation, chemical modifying, excellent plasticity and so on. In recent years, it has been widely used in organic electronic devices.8-hydroxyquinoline metal complexes and 10-hydroxybenzo[h]quinolinato metal complexes have been widely used in organic light-emitting diodes, organic spin valves and other electronic devices in view of their good thermal stability and high fluorescence quantum efficiency (FQE).Although the organic semiconductors have weak spin-orbit coupling and hyperfine interactions, which makes them ideal for spin-polarized electron injection and transport applications, yet the experimental spin diffusion lengths and FQE in organic films are greatly lower than the theoretical expectation. It can be attributed to the disorders, defects, impurities and traps in amorphous films which were prepared by vacuum deposition or spin coating. Therefore, this problem might be, at least partially, overcome by using organic crystals. And high-quality organic semiconductor single crystals have stable structure, high mobility, thermal stability and high FQE will greatly improve the performance of the devices as well as the research of intrinsic physical properties and spin transport properties.In this dissertation, we propose a process for preparing high-quality organic semiconductor crystals, the products we obtained have single crystal structure and the size in micro/nano scale, which suit to fabricate organic spintronic devices or organic light emitting devices. For example, the crystalline Beq2 and Bebq2 were prepared by using physical vapor transport (PVT), Physical Vapor Deposition (PVD) and solution method, the structural and optical properties of the samples are also investigated.The detailed contents and main results are given below:Firstly, Beq2 and Bebq2 crystals were prepared by PVT method. The structural properties and the qualities of the samples were studied by XRD and FTIR, respectively. In addition, the photoluminescence (PL) spectra of the Beq2 and Bebq2 crystals were also performed. The PL peaks of the Beq2 crystals with rodlike shape locates at between 507 nm and 516 nm and the PL peaks of the Bebq2 bulk crystals at between 501nm and 510 nm. The PL peaks of the Bebq2 dodecahedron crystals between 508 nm and 512 nm. The PL peak wavelength belong to green light emitting materials. By CIE 1931 chromaticity coordinate diagram, a detailed study of the nature of their relatively light emission peak emission chromaticity and singleness.Secondly, Beq2 and Bebq2 crystals were prepared by using the method of PVD. The structural properties and the qualities of the prepared Beq2 and Bebq2 crystals were studied by XRD and FTIR. Subsequently, the photoluminescence (PL) spectra of the Beq2 and Bebq2 crystals were studied. The PL peaks of the Bebq2 lamellar crystals near 503 nm. The position of PL peak has relationship with the size of Bebq2 crystal, for example, the PL peak of smaller one at 513 nm, which belongs to green light emitting.Thirdly, bis(10-hydroxybenzo[h]quinolinato) beryllium crystals were prepared by solution method. Chloroform was chosen as the organic solvent, three different concentrations of Bebq2 solutions were made. The Bebq2 molecules were self-assembly with the volatilization of chloroform, and hexahedral crystals were obtained. A possible growth mechanism was proposed in this paper. The structural properties and the qualities of the prepared Bebq2 crystals were studied by XRD and FTIR, respectively.Finally, Beq2 and Bebq2 film were prepared by using vacuum thermal evaporation equipment on glass, silicon and SiO2 substrates, respectively. The photoluminescence (PL) and IR transmission spectra of the Beq2 and Bebq2 film were studied. The optical band gap of bis(8-hydroxyquinolinato) beryllium and bis(10-hydroxybenzo[h]quinolinato) beryllium is 2.75 eV and 2.75 eV, respectively. It can be seen that the PL intensity of Beq2 and Bebq2 film has close connection with the substrate. The PL intensity of the two films fabricated on Si substrates is significantly higher than that on the SiO2 substrates. Furthermore, the PL intensity of Beq2 and Bebq2 crystals were significantly better than the films of Beq2 and Bebq2, respectively.