Liu Shu-Man

Optical properties of strongly luminescing mercaptoacetic-acid-capped ZnS nanoparticles

We synthesized zinc sulfide nanoparticles with mercaptoacetic acid as capping agent and obtained nanoparticles of different sizes. The optical properties of ZnS nanoclusters were studied by optical absorption and photoluminescence. High sample quality is reflected in sharp absorption features and strong band edge emission, which is tunable with particle size. The selectively excited luminescence properties and the coupling between electronic and vibrational excitation in ZnS nanoparticles are discussed.

Effect of aging on CdSe nanocrystals

Abstract The effect of aging on surface stabilized CdSe nanocrystals samples has been studied through UV-vis absorption and PL measurements. The UV-vis absorption showed that the absorption maximum shifted to lower energy and the optical density became stronger with aging time. The PL measurements showed that the luminescence intensity increases with aging. The emissions associated with the band edge and shallower trap shifted to lower energy with aging time, whereas that associated with deep traps does not.

Photoluminescence of Eu2+ doped ZnS nanocrystals

Eu2+ doped ZnS nanocrystals exhibit new luminescence properties because of the enlarged energy gap of nanocrystalline ZnS host due to quantum confinement effects. Photoluminescence emission at about 520 nm from Eu2+ doped ZnS nanocrystals at room temperature is investigated by using photoluminescence emission and excitation spectroscopy. Such green emission with long lifetime (ms) is proposed to be a result of excitation, ionization, carriers recapture and recombination via Eu2+ centers in nanocrystalline ZnS host.

High-Power and High-Efficiency Operation of Terahertz Quantum Cascade Lasers at 3.3 THz

A high-power and high-efficiency GaAs/AlGaAs-based terahertz (THz) quantum cascade laser structure emitting at 3.3 THz is presented. The structure is based on a hybrid bound-to-continuum transition and resonant-phonon extraction active region combined with a semi-insulating surface-plasmon waveguide. By optimizing material structure and device processing, the peak optical output power of 758 mW with a threshold current density of 120 A/cm2 and a wall-plug efficiency of 0.92% at 10K and 404mW at 77K are obtained in pulsed operation. The maximum operating temperature is as high as 115 K. In the cw mode, a record optical output power of 160 mW with a threshold current density of 178 A/cm2 and a wall-plug efficiency of 1.32% is achieved at 10 K.

Metalorganic Chemical Vapor Deposition Growth of InAs/GaSb Superlattices on GaAs Substrates and Doping Studies of P-GaSb and N-InAs

InAs/GaSb type-II superlattices (SLs), Zn-doped GaSb and Si-doped InAs were grown on semi-insulating (001) GaAs substrates by metalorganic chemical vapor deposition. X-ray diffraction reveals that complete strain compensation between the SLs and the GaSb buffer layer is achieved in our SL samples. The relationship between the hole concentration p in GaSb and the diethylzinc (DEZn) flow rate is p ∝ [DEZn]0.57. The electron concentration in InAs does not show good linearity with the SiH4 flow rate. The growth rate of the p-GaSb epilayer is decreased as the DEZn mole fraction increases, while the growth rate of the n-InAs epilayer is weakly dependent on the SiH4 flow rate.

Carrier transport behaviour of molecular doped poly (N-vinylcarbozole) in polymer light-emitting diodes

Single-layer polymer light-emitting diodes are prepared from blends of poly(N-vinylcarbozole) (PVK) doped with tris(8-hydroxy-quinoline) aluminium (Alq3) of 2 wt% (sample a) and 0.2 wt% (sample b). The onset of PVK transient electroluminescence (EL) is delayed with respect to that of Alq3 in sample a under pulsed excitation, while the EL onsets of Alq3 and PVK in sample b are simultaneous. The total carrier mobility of the Alq3-rich regions in sample a is larger than that of the PVK-rich regions. However, the total carrier mobility is homogeneous in sample b. The phase image of atomic force microscopy and photoluminescence spectra of samples a and b indicate that the separated phase of samples a and b exists in the PVK-rich and Alq3-rich regions. The variance of the doping concentration and separated phase in blends results in the different carrier transport mobility of Alq3-rich and PVK-rich regions.

Fabrication of Low-Density Long-Wavelength InAs Quantum Dots using a Formation-Dissolution-Regrowth Method

Low-density (~109 cm−2), long-wavelength (more than 1300 nm at room temperature) InAs/GaAs quantum dots (QDs) with only 1.75-mono-layer (ML) InAs deposition were achieved by using a formation-dissolution-regrowth method. Firstly, small high-density InAs QDs were formed at 490°C, then the substrate temperature was ramped up to 530°C, and another 0.2 ML InAs was added. After this process, the density of the InAs QDs became much lower, and their size became much larger. The full width at half maximum of the photoluminescence peak of the low density, long-wavelength InAs QDs was as small as 27.5 meV.