Huanying Li

Temperature dependence of luminescence characteristics of Lu2(1−x)Y2xSiO5:Ce3+ scintillator grown by the Czochralski method

In this paper, we investigate the temperature dependence of luminescence characteristics of highly efficient cerium-doped scintillator, lutetium-yttrium orthosilicate Lu2(1−x)Y2xSiO5:Ce3+. The photoluminescence excitation and emission spectra have been measured in a broad temperature range. The temperature dependence of the Ce1 and Ce2 decay times shows the onset of decay time decrease at about 300 K. This observation demonstrates that unlike so far reported, the Ce2 center is not substantially quenched until room temperature. The 5d1 excited-state ionization of both Ce1 and Ce2 centers is studied by purely optical methods.

Annealing effects on Czochralski grown Lu2Si2O7:Ce3+ crystals under different atmospheres

Cerium-doped lutetium pyrosilicate Lu2Si2O7:Ce3+ (LPS:Ce) single crystal samples grown via Czochralski method were annealed under air and H2 atmospheres from 350to1600°C. The x-ray excited luminescence spectra and UV as well as thermal stimulated luminescence spectra were measured. It was found that the luminescence efficiency after annealing in air at 1400°C was significantly enhanced compared to the unannealed samples. This phenomenon was suggested to be caused by the existence of some oxygen vacancies in the LPS:Ce crystals, and these oxygen vacancies can be effectively eliminated by means of annealing in air. Although the annealing will lead to the oxidization of cerium ions from Ce3+ ions to Ce4+, which is harmful to the luminescent efficiency, the annealing treatment does enhance the luminescent efficiency of LPS:Ce, without changing its luminescence mechanics.

Analysis of atomic force microscopic results of InAs islands formed by molecular beam epitaxy

Atomic force microscopy (AFM) measurements of nanometer-sized islands formed by 2 monolayers of InAs by molecular beam epitaxy have been carried out and the scan line of individual islands was extracted from raw AFM data for investigation. It is found that the base widths of nanometer-sized islands obtained by AFM are not reliable due to the finite size and shape of the contacting probe. A simple model is proposed to analyze the deviation of the measured value From the real value of the base width of InAs islands

Structural characterization of InGaAs/GaAs quantum dots superlattice infrared photodetector structures

InGaAs/GaAs quantum dots (QDs) superlattice grown by molecular beam epitaxy (MBE) at different substrate temperatures for fabricating 8–12 μm infrared photodetector were characterized by transmission electron microscopy (TEM), double-crystal X-ray diffraction (DCXRD) and photoluminescence (PL). High-quality QDs superlattice can be achieved by higher growth temperature. Cross-sectional TEM shows the QDs in the successive layers are vertically aligned along growth direction. Interaction of partial vertically aligned columns leads to a perfect vertical ordering. With increasing number of bilayers, the average QDs size becomes larger in height and rapidly saturates at a certain value, while average lateral length nearly preserves initial size. This change leads to the formation of QDs homogeneous in size and of a particular shape. The observed self-organizations are attributed to the effect of strain distribution at QDs on the kinetic growth process. DCXRD measurement shows two sets of satellite peaks which corresponds to QDs superlattice and multi quantum wells formed by the wetting layers. Kinematical simulations of the wetting layers indicate that the formation of QDs is associated with a decrease of the effective indium content in the wetting layers.

Influence of RE Doping on the Scintillation Properties of LSO Crystals

Rare Earth (RE) such as Y, La, Sc and Gd ions doped Ce:Lu2SiO5 (LSO) crystals, were grown by Czochralski method. The concentrations of these RE ions in LSO crystals were measured, and their segregation coefficients were calculated according to the concentrations. La3+ was found to be helpful to increase the segregation coefficients of Ce3+ in LSO crystals. Transmission, UV and X-ray excited emission spectra, and UV light emission decay curves of RE-doped LSO crystals were tested at room temperature. No significant difference in emission spectra and decay time can be identified among these RE-doped LSO crystals. Doping with La3+ may improve the energy resolution and photoelectron yield of LSO crystals.

InAs quantum dots in InAlAs matrix on (0 0 1)InP substrates grown by molecular beam epitaxy

InAs quantum dots grown on InAlAs lattice-matched to (0 0 1) InP substrates by molecular beam epitaxy are investigated by double-crystal X-ray diffraction, photoluminescence and transmission electron microscopy. The growth process is found to follow the Stranski-Krastanow growth mode. The islands formation is confirmed by the TEM measurements. Strong radiative recombination from the quantum dots and the wetting layer is observed, with room temperature PL emission in the 1.2-1.7 mu m region, demonstrating the potential of the InAs/InAlAs QDs for optoelectronic device applications

Luminescence Properties and Their Temperature Dependence of

Cerium-doped lutetium pyrosilicate (LPS:Ce) crystal with dimension of Φ 10 × 40 mm was grown successfully by Czochralski method. Its crystal structure was determined to be monoclinic with space group of C2/m. The optical transmission, UV and X-ray excited emission spectra, as well as decay curves were measured from 77 K to 500 K. Two emission peaks, 380 nm and 403 nm result from the transition of electrons from 5d1 to two ground levels (2F5/2 and 2F7/2) of Cerium ions (Ce3+) in the LPS:Ce crystals. The decay time of the fluorescence is weakly increasing from 77 K to 400 K and then decreases sharply. The light output of LPS:Ce can be improved greatly by annealing at 1400°C in air. TSL peak at 543 K in LPS:Ce is suggested to be related to oxygen vacancies which are one of the reasons of the poor light output.

{\rm Lu}_{2}{\rm Si}_{2}{\rm O}_{7}:{\rm Ce}

Good UV transmittance and some scintillation light are two requirements for materials to be used to construct a homogeneous hadron calorimeter (HHCAL) capable to measure both Cherenkov and Scintillation light. In this paper we report an investigation on lead based halide crystals for the HHCAL detector concept, including lead fluoride chloride (PbFCI) and gadolinium doped lead fluoride (PbF2:Gd) crystals grown at Shanghai Institute of Ceramics. The optical and scintillation properties of PbFCI and PbF2:Gd crystal samples, such as transmittance and photo-/x- luminescence spectra, light output and corresponding decay time, were measured at room temperature. Excellent UV cutoff edge and short decay time were found in PbFCI crystals. Further development work to improve PbFCI quality for the HHCAL project is discussed.

Scintillation Crystals

We report room temperature low current density of InP-based AlInAs/InGaAs quantum cascade laser (QCL). For a 7.66-mum QCL, the threshold current density of 1.7 kA/cm2 at 300 K, pulsed output power of 800 mW at 80 K, and continuous-wave (CW) output power of 13 mW at 135 K are achieved. An 8.91-mum QCL comprised 100 stage active region operating up to 320 K in pulsed mode also presented.