Recent Developments in Functional Crystals in China

Functional crystals are the basic materials for the development of modern science and technology and are playing key roles in the modern information era. In this paper, we review functional crystals in China, including research history, significant achievements, and important applications by highlighting the most recent progress in research. Challenges for the development of functional materials are discussed and possible directions for development are proposed by focusing on potential strengths of these materials.

Spectroscopic Properties of Ce:YAP Scintillation Crystal Grown by Temperature Gradient Technique

Spectroscopic properties of Ce-doped yttrium orthoaluminate （Ce：YA1O3 or Ce：YAP） crystals gown by temperature gradient technique （TGT） were investigated, and the effects of the growth conditions on the properties were analyzed. Methods of optical absorption （OA）, photoluminescence （PL）, photoluminescence decay （PLD）, X-my excited luminescence （XL） and cathodeluminescence （CL） were used in these investigations. The results showed that the absorption band peak at 202,394 and 532 nm originated from F and F^＋ color center induced by the weak reducing growth atmosphere, green emission band near 500 nm derived from Ce3^＋ -Ce^3＋ pairs and band at 650 - 850 nm from some unintentional impurity in crystals.

闪烁晶体——辐射探测用单晶

Phosphor converts excitation energy into light,resulting in lumminescence.The luminescence caused by radiation is called scintillation.Since the discovery of the scintillation in NaI∶Tl crystal in 1948,a series of materials with profound scintillating characteristics have been developed and have found wide applications for radiation detection in different fields such as nuclear physics,high energy physics,medical diagnostic imaging,geophysics exploration,clandestine explosive finding and many industrial measuring systems. Inorganic scintillating crystals have superior characteristics over their organic counterparts and some kinds of ceramics,glasses and powders that do have their scintillation effects.We will confine ourselves mainly to inorganic scintillating crystals in this presentation..

Color center and radiation center in Lu_2SiO_5:Ce crystal

Radiation damage of Lu2SiO5：Ce （LSO：Ce） crystals was investigated through intense UV light. An absorption band at 435 nm was observed in the transmission spectrum of the damaged LSO：Ce crystal, similar to that of absorption band caused by gamma ray irradiation. GDMS analysis for LSO：Ce crystals revealed the existence of impurities, such as Yb in the crystals. The impurities might be responsible for the optical absorption of the color center and the radiation center.

Photoluminescence, scintillation and thermally-stimulated luminescence properties of Tb-doped 12CaO·7Al2O3 single crystals grown by FZ method

Tb-doped 12CaO·7Al_2O_3（Tb：C12A7） crystals were synthesized by the floating zone（FZ） method and the photoluminescence（PL）, scintillation and thermally-stimulated luminescence（TSL） properties were investigated. The photoluminescence（PL） emission spectra and PL decay time profiles were investigated by using Quantaurus-tau（Hamamatsu）. The scintillation spectra and decay time profiles were measured by using our laboratory-constructed set-up under X-ray irradiation. Finally, TSL glow curve was measured by using Nanogray TL-2000 with the heating rate of 1 °C/s. In PL and scintillation, emission peaks were observed at 493, 543, 587 and 620 nm due to the 4f-4f transitions of Tb3~＋. Decay time constants of the emission by PL and scintillation appeared to be different, and the measured values were approximately 2.4 and 1.9 ms, respectively. After X-ray irradiations, the 0.5%（all Tb contents in this paper are in mole fraction） and 1.0% Tb-doped samples showed a single intense and broad glow peak around 100 oC while 1.2%–1.5% Tb-doped samples showed notable additional peak around 250 oC.

高能物理研究用钨酸铅闪烁晶体的辐照损伤机理研究

In high energy physics experiments,large arrays of scintillation crystals have b een used in electromagnetic calorimeters for precision measurements of photons a nd electrons.The large crystal calorimeters and their use has been a key factor in the high energy physics programs.Table 1 lists parameters of crystal calorime ter projects of the past (Crystal Ball),present(L3) and future (CMS) in high ene rgy physics.In future high energy collider,however,scintillating crysta ls face a new challenge:the radiation damage caused by the increased background radiation level.It would reach about 1000 rad/day for lead tungstate (PbWO 4) crystal at LHC.Lead tungstate is a new fast and dense scintillating crystal and has been s elected as scintillator for the construction of calorimeter in CMS experiment of Large Hadron Collider (LHC) at CERN(European Organization for Nuclear Research ) next century.82000 large sized PWO scintillating crystals will be assembled in the calorimeter of the CMS experiment,and they will be produced both in China a nd in Russia from now until to 2004.

Comparison of two position sensitive gamma-ray detectors based on continuous YAP and pixellated NaI(TI) for nuclear medical imaging applications

Dedicated position sensitive gamma-ray detectors based on position sensitive photomultiplier tubes （PSPMTs） coupled to scintillation crystals, have been used for the construction of compact gamma-ray imaging systems, suitable for nuclear medical imaging applications such as small animal imaging and single organ imaging and scintimammography. In this work, the performance of two gamma-ray detectors： a continuous YAP scintillation crystal coupled to a Harnamastu R2486 PSPMT and a pixellated NaI（TI） scintillation array crystal coupled to the same PSPMT, is compared. The results show that the gamma-ray detector based on a pixellated NaI（TI） scintillation array crystal is a promising candidate for nuclear medical imaging applications, since their performance in terms of position linearity, spatial resolution and effective field of view （FOV） is superior than that of the gamma-ray detector based on a continuous YAP scintillation crystal. However, a better photodetector （Hamamatau H8500 Flat Panel PMT, for example） coupled to the continuous crystal is also likely a good selection for nuclear medicine imaging applications.