Dingzhong Shen

A study on yttrium doping in lead tungstate crystals

In this paper we present results of a study on the yttrium doping in lead tungstate crystals. The crystal growth by modified Bridgman method is described. Results of trace analysis on raw materials and crystals are presented. The segregation coefficient of yttrium ions in lead tungstate crystals was determined. The scintillation emission and longitudinal transmittance spectra, light output, decay kinetics, light response uniformity and radiation damage were measured. It is found that yttrium doping suppresses slow scintillation component and improves radiation hardness of lead tungstate crystals.

Growth of NaBi(WO4)2 crystal by modified-Bridgman method

Abstract NaBi(WO4)2 (NBW) crystals have been grown for the first time by modified-Bridgman method. Influences of some factors on the crystal growth process are discussed. X-ray powder diffraction experiments show that the unit cell parameters of NBW crystal are a=b=0.5284xa0nm, c=1.1517xa0nm, and V=0.3215xa0nm3. The differential thermal analysis shows that the NBW crystal melts at 923°C.

Suppression of yellow luminescence in As-doped GaN epilayers grown by metalorganic chemical vapor deposition

The excitonic emissions near band edge, the donor-to-acceptor pair (DAP) emissions and the yellow luminescence (YL) in undoped GaN and As-doped GaN at a low doping level have been investigated. At 4.2 K, the intensity of the DAP emissions around 3.28 eV were observed to increase when the As concentration is increased. This enhancement has been correlated with an increase of the As-related isoelectronic centers. On the other hand, a remarkable reduction of the yellow luminescence due to the incorporation of As into GaN is found at 4.2 K, and it persists up to room temperature where the DAP signal has got quenched due to thermal ionization. These results suggest that the suppression of the YL is due to the passivation of the YL deep centers by the As-incorporation.

A high-density inorganic scintillator: lead fluoride chloride

Lead fluoride chloride (PbFCl) crystal, whose density is about 7.11 g cm−3, was grown by the modified Bridgman method. PbFCl can emit violet-blue light with the peaks at 392 and 420 nm when excited by ultraviolet light or x-rays. The light yield of PbFCl under irradiation of 137Cs is about 20% as that of bismuth germanate. A fast and a slow decay time with 4 ns and 35 ns, respectively, were obtained when PbFCl was studied with a pulsed x-ray facility. The irradiation resistivity of PbFCl was studied by applying 60Co. The results of the experiments indicate that PbFCl is a new inorganic scintillator.

New types of lead tungstate crystals with high light yield

Abstract Because of their high stopping power and fast scintillation, lead tungstate crystals have attracted much attention in the high energy physics and nuclear physics communities. The use of lead tungstate, however, is limited by its low light output. An effort has been made at the Shanghai Institute of Ceramics to improve this. The results indicate that a factor of ten increase of the light output, mainly in the microsecond decay component, may be achieved. The photo luminescence spectrum, light output and decay kinetics of new samples are presented. Longitudinal uniformity of a sample of 22xa0radiation lengths is studied. Possible applications for calorimetry in high energy and nuclear physics experiments are discussed.

Crystal growth of PbFCl by modified Bridgman method

Abstract Lead fluoride chloride (PbFCl) crystal was grown by modified Bridgman method. The result of X-ray powder diffraction pattern (XRD) was well accordant with the data of JCPDS card. The transmittance spectrum was first reported without absorption band from 270 to 800xa0nm. Three emission bands were first observed at room temperature when excited by ultraviolet light.

Crystal growth and optical anisotropy of Y:PbWO4 by modified Bridgman method

Abstract Large-size yttrium-doped lead tungstate single crystals (Y:PbWO 4 ) of good quality were grown by modified Bridgman method. The growth conditions, such as purity of raw materials, growth orientation and rate, temperature gradient, seed selection and cooling rate of after-growth, were discussed in this paper. Data of crystals along different growth orientations were obtained on the transmittance spectra, and the radio- and photoluminescence emission spectra. Optical anisotropy effects of Y:PbWO 4 were observed and studied.

Yttrium-doped lead tungstate crystals

In this paper we present results of a study on the yttrium doping in lead tungstate crystals. The crystal growth by modified Bridgman method is described. Results of trace analysis on raw materials and crystals are presented. The segregation coefficient of yttrium ions in lead tungstate crystals was determined. The scintillation emission and longitudinal transmittance spectra, light output, decay kinetics, light response uniformity and radiation damage were measured. It is found that yttrium doping suppresses slow scintillation component and improves radiation hardness of lead tungstate crystals.

Structural defects and characteristics of lead fluoride (PbF2) crystals grown by non-vacuum Bridgman method

A non-vacuum growth technique for pure cubic PbF2 crystal was reported in this paper. It used a chemical as a scavenger to deprive the oxygen impurities in the raw materials and growth system and realized the growth of PbF2 crystals under non-vacuum conditions. The needle-like defect existing in lead fluoride crystals was identified to be an orthorhombic phase of PbF2 crystal. It can be eliminated effectively when annealed within a reduction atmosphere and at a temperature higher than 3651C. PbF2 crystals grown with this method are characterized with a wide transparent region from 240 nm to 16.7mm, a good energy resolution of 3:2%=OE; and a very high radiation hardness. r 2002 Elsevier Science B.V. All rights reserved.

Transmission loss of lead fluoride crystals induced by oxygen contamination

Cubic PbF2 crystals were grown by non-vacuum modified Bridgman method. Their optical transmission may easily be deteriorated by oxygen contamination during their growth process, annealing and afterwards machining, storing and carrying. It was found that the role of oxygen is to promote the transformation of b-a phase in the initial cubic structured monocrystals, which results in the formation of cryptocrystalline or microlithic texture composed of crystalline a-PbF2 grains. This texture is suggested to be responsible for the transmission loss of lead fluoride (PbF2) crystals. And the oxygen does not appear in the form of oxide, but in a dissociated form in PbF2 crystals. r 2002 Elsevier Science B.V. All rights reserved.