Guo Chang-Xin

The synthesis of one-dimensional controllable ZnO microrods

Various morphology ZnO submicrorods and microrods have been fabricated onto glass substrates through chemical solution growth by the source of zinc acetate (Zn(CH3COO)2.2H2O) and hexamethylene tetraamine ((CH2)6N4). We discuss the influence of PH and the concentration of the solution on the shapes of the as-synthesized ZnO samples. And analyse the growth mechanism. The regular hexagonal ZnO rods align has been made by control of a certain concentration and proper PH. The hexagonal ZnO columns mainly grew in the [002] direction. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) are used to characterize the structure, the morphology and optical property of the samples. The photoluminescence spectrum of hexagonal ZnO columns shows that there are a broad strong red band (650nm) and a broad band in short wavelength which are two overlapped emission bands with the peaks at about 380nm and 430nm.The UV emission (~387nm) comes from recombination of free excitons. The blue emission with peak at 430nm is assigned for the recombination from an electron at interstitial Zn to a hole in VB. The red emission at 650nm is ascribed to the recombination from an electron at Vo2+ to a hole in VB.

Photoluminescence of Eu(III)-Doped ZnO Nanopowder and Energy Transfer from ZnO to Eu(III) Ions

An europium(III)-doped ZnO (ZnO:Eu3+) nanopowder has been directly synthesized by a high-temperature calcination method. Under the typical UV ZnO excitation, Eu3+-doped samples exhibit strong red luminescence from Eu3+ ions with complete quenching broad emission. An energy transfer from ZnO host to Eu3+ ions can be observed.

A high-resolution electron microscopy study of microstructure of ZnS powder phosphors with different dopants

Abstract The microstructures of ZnS phosphors with different dopants and different luminescence mechanisms have been investigated by transmission electron microscopy (TEM). Our observations show that there are evident differences in the microstructures of ZnS: Fe, ZnS: Cu and ZnS: Mn. It is reasonable to infer from the TEM experiments that the photoluminescence probably relates mainly to the various stacking faults and dislocations, whereas the a.c. electroluminescence may have a relationship with the microtwin structure, and the coherent growth state of α- and β-phases may be the reason for the d.c. electroluminescence.

Fabrication and photoelectrical characteristics of ZnO nanowire field-effect transistors

The fabrication and photoelectrical characteristics of suspended ZnO nanowire (NW) field-effect transistors (FETs) are presented. Single-crystal ZnO NWs are synthesized by a hydrothermal method. The fabricated FETs exhibit excellent performance. When Vds = 2.5 V, the peak transconductance of the FETs is 0.396 μS, the average electron mobility is 50.17 cm2/(V s), the resistivity is 0.96 × 102 Ω.cm at Vgs = 0 V, and the current on/off ratio (Ion/Ioff) is approximately 105. ZnO NW-FET devices exposed to ultraviolet radiation (2.5 μW/cm2) exhibit punch-through and threshold voltage (Vth) shift (from −0.6 V to +0.7 V) and a decrease by almost half of the source-drain current (Ids, from 560 nA to 320 nA) due to drain-induced barrier lowering. Continued work is underway to reveal the intrinsic properties of suspended ZnO nanowires and to explore their device applications.

High pressure effect on the luminescence spectra of Eu3+ in stoichiometric host microcrystals

Abstract Na 5 Eu(MoO 4 ) 4 and Na 5 Eu(WO 4 ) 4 are two good stoichiometric host luminescent materials having high concentrations of Eu 3+ . The effect of hydrostatic high pressure on their luminescent spectra has been investigated. The emission spectra of Na 5 Eu(MoO 4 ) 4 and Na 5 Eu(WO 4 ) 4 were measured at pressures up to 40 kbar and 80 kbar, respectively, using a high pressure microspectroscopic system in conjunction with a gasketed diamond anvil cell at room temperature. The red shift of the emission lines and energy levels under high pressure have been measured. According to crystal field theory, the pressure dependence of the crystal field parameters have been deduced from the experimental data.

Enhancement mechanism of luminescence of RE3+ (Eu3+, Sm3+, Dy3+) in Y2O2S phosphor by a trace of Tb3+

The enhancement effects of cathodluminescence (CL) and photoluminescence (PL) of Eu3+, Sm3+ and Dy3+ in Y2O2S by a trace of Tb3+ have been investigated. The reasons for the enhancement are (1) decreasing of charge accumulation on sample surface by addition of Tb3+, (2) existing energy transfer from Tb3+ to RE3+. The mechanism of energy transfer are discussed and a model of energy transfer of free excitons is proposed.

Characterization of ZnO nanowire field-effect transistors exposed to ultraviolet radiation

A ZnO nanowire (NW) field-effect transistor (FET) is fabricated and characterized, and its characterization of ultraviolet radiation is also investigated. On the one hand, when the radiation time is 5 min, the radiation intensity increases to 5.1 μW/cm2, while the saturation drain current (Idss) of the nanowire FET decreases sharply from 560 to 320 nA. The field effect mobility (μ) of the ZnO nanowire FET drops from 50.17 to 23.82 cm2/(V·s) at VDS = 2.5 V, and the channel resistivity of the FET increases by a factor of 2. On the other hand, when the radiation intensity is 2.5 μW/cm2, the DC performance of the FET does not change significantly with irradiation time (its performances at irradiation times of 5 and 20 min are almost the same); in particular, the Idss of NW FET only reduces by about 50 nA. Research is underway to reveal the intrinsic properties of suspended ZnO nanowires and to explore their device applications.

Density of states and energy levels of BaF2:Sm2+ using nonrelativistic and relativistic cluster models

Abstract Density of states and energy levels for BaF2:Sm2+ are calculated self-consistently, using both one-electron local density discrete variational non-relativistic Hartree-Fock-Slater (HFS) and relativistic Dirac-Slater (DS) cluster models. The finite clusters calculated include SmF8 and SmF8Ba12 for BaF2:Sm2+, which are embedded in a crystal environment. The spin-orbit coupling parameter ζ4f derived from the DS model is equal to 1247 cm−1. The energy gap derived from the HFS model with SmF8Ba12 clusters embedded in the crystal is 9.56 eV, which is near the experimental results.