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1.
D. Cavouras I. Kandarakis T. Maris G.S. Panayiotakis C.D. Nomicos 《Applied Physics A: Materials Science & Processing》2001,72(1):67-72
In information theory, entropy expresses the information gain obtained after detection of a signal concerning the state of
a parameter of interest. In this study, entropy has been expressed in terms of physical quantities (emitted optical fluence
and MTF) related to the imaging performance of phosphor materials, which are employed in medical imaging radiation detectors.
Four phosphor materials, used in the form of laboratory-prepared fluorescent layers (screens), were compared on the basis
of their entropy performance. Measurements were performed using 30- and 80-kVp X-ray beams often employed in X-ray imaging.
Results showed that phosphor materials with high density and effective atomic number exhibit high entropy performance, especially
at the higher X-ray tube voltage of 80 kVp. Entropy values are also affected by the type of activator, which determines the
intrinsic X-ray-to-light conversion efficiency, and the spectrum of emitted light. The proximity of the incident X-ray quanta
energy to the energy of the K-shell threshold for photoelectric absorption is an additional important factor which increases
entropy. This effect was more apparent in the performance of yttrium-based phosphors at the lower voltage of 30 kVp.
Received: 7 January 2000 / Accepted: 28 March 2000 / Published online: 23 August 2000 相似文献
2.
N. Kalivas L. Costaridou I. Kandarakis D. Cavouras C.D. Nomicos G. Panayiotakis 《Applied Physics A: Materials Science & Processing》1999,69(3):337-341
The quality of a medical image depends, among other parameters, on quantum noise. Quantum noise is affected by the fluctuations
in the number of optical quanta produced within the phosphor, per absorbed X-ray (i.e. phosphor intrinsic-gain fluctuations).
This effect is considered by means of a factor, called in this study intrinsic-gain noise factor, IGNF(E). In existing theoretical
models of quantum noise, the corresponding factor is taken to be equal to one. In this paper, an expression that accounts
for the coefficient of variation of the phosphor intrinsic gain is introduced. This expression takes into account the process
of electron–hole pair conversion to optical photons and the frequency distribution function of the emitted optical photon
energy. Subsequently IGNF(E) is expressed in terms of this coefficient of variation. IGNF(E) has been calculated for several
phosphors and for various energies. For all medical X-ray energies studied, phosphors that exhibit a high relative fluctuation
of emitted optical photon energy, IGNF(E) exceeds by 2% to over 17% the corresponding factor of the existing theoretical models
of quantum noise.
Received: 25 March 1999 / Accepted: 29 March 1999 / Published online: 14 July 1999 相似文献
3.
I. Kandarakis D. Cavouras C.D. Nomicos G.S. Panayiotakis 《Applied physics. B, Lasers and optics》1999,68(6):1121-1124
This study presents a method to evaluate the imaging performance of phosphor materials used in medical imaging systems. The
advantage of the method is that phosphor evaluation is performed independently of the optical detectors (films, photocathodes,
photodiodes) used in radiation detectors to capture phosphor light. The method is based on the noise-equivalent-quanta (NEQ)
concept, which provides an index of the signal-to-noise ratio (SNR) associated with the diagnostic value of a medical image.
NEQ was expressed as a function of the phosphor’s emitted light wavelength, light energy flux, and modulation transfer function
(MTF). All these parameters are related to intrinsic phosphor properties such as effective atomic number, density, activator
ion. The method was tested on three yttrium-based phosphors, two of them activated with europium (Eu3+) and one with terbium (Tb3+). Results showed that europium-activated phosphors (Y2O2S:Eu, Y2O3:Eu) exhibited improved SNR, whereas the terbium phosphor (Y2O2S:Tb) had better MTF.
Received: 11 August 1998 / Revised version: 4 January 1999 / Published online: 10 March 1999 相似文献
4.
G. Panayiotakis D. Cavouras I. Kandarakis C. Nomicos 《Applied Physics A: Materials Science & Processing》1996,62(5):483-486
The X-ray luminescence efficiency of laboratory-prepared YVO4: Eu screens and their spectral compatibility to common optical detectors were studied under medical fluoroscopy conditions. YVO4: Eu screens were prepared by sedimentation and with different coating thickness. Luminescence efficiency of the YVO4: Eu screens was measured at various X-ray tube voltages (50–250 kVp) and for screens of different coating thicknesses (20–180 mg/cm2). Spectral response was also measured and spectral matching factors between the YVO4: Eu screens and some common optical detectors (photocathodes, photodiodes, photographic emulsion) were calculated. Experimental results on efficiency were fitted by formulas of the theoretical model developed by Hamaker and Ludwig in order to determine phosphor intrinsic X-ray-to-light conversion efficiency and intrinsic optical characteristics, such as coefficients related to light scattering and absorption. Although the luminescence efficiency of YVO4: Eu screens was found to be relatively low (3–11 M s/mR m2), the matching factor of YVO4 : Eu screens with some red sensitive optical detectors was excellent, of the order of 0.96. High spectral compatibility may indicate that YVO4: Eu scintillators could be used in medical image detectors. 相似文献
5.
A study of some optical properties of hafnium dioxide (HfO2) thin films and their applications 总被引:1,自引:0,他引:1
M. Fadel O.A. Azim M. O.A. Omer R.R. Basily 《Applied Physics A: Materials Science & Processing》1998,66(3):335-343
2 ), a series of films ranging in thickness from 50 to 10000 nm was prepared by using an electron beam gun inside an evacuated
coating chamber of pressure 1×10-5 mbar. The films were obtained on optical glass substrate by using oxygen with a backfill pressure of 2.4×10-4 mbar during the deposition processes. The optical constants of the films were computed in the spectral wavelength region
(350–2000 nm) from the transmission, reflection and thickness measurements. A computer program was created to determine two
optical parameters n and k of the films, and this was achieved by entering the practical results into the computer program,
which solved a series of equations for each wavelength. The effects created by changing various evaporation conditions (thickness,
substrate temperature and evaporation rate) were studied in the spectral wavelength range, and the optimum values of the various
conditions were obtained while achieving the best optical performance. According to the investigations of the HfO2 material, two applications of the anti-reflection (AR) multi-layer coatings were achieved in two different spectral wavelength
ranges. The first application was measured in the visible and near infra-red (VIS/NIR) range from 500 nm to 850 nm deposited
on the glass substrate. The second application was measured in the infrared (IR) range from 7500 nm to 11500 nm deposited
on germanium substrate. Computer modelling for designing the optical multi-layer system has been presented. The theoretical
formulation and experimental results with the same specification were achieved. The correlation between the theoretical and
the experimental results reveals a close agreement that offers a convenient method for predicting and controlling the multi-layer
coating. By continuous measurement of the optical and mechanical (durability) performances of the coating process, high-quality
films were produced in the manufacture of various optical devices.
Received: 16 April 1997/Accepted: 5 August 1997 相似文献
6.
D. Kip B. Kemper I. Nee R. Pankrath P. Moretti 《Applied physics. B, Lasers and optics》1997,65(4-5):511-516
0.61 Ba0.39Nb2O6, SBN61), either by proton or helium ion implantation. Proton-implanted samples show a large increase of dark conductivity
that reduces or even prevents the recording of refractive index gratings. For waveguides formed by helium implantation this
effect is absent, and they can be used for efficient holographic recording. Photorefractive properties of the waveguides are
investigated by two-beam coupling. After implantation with 2.0 MeV He+ and doses of (0.5-5)×1015 cm-2, the samples have to be polarized again, because heating or charge effects at the crystals surface during the implantation
process decreases or even reverses the effective electrooptic coefficients in the waveguiding layer. For repoled samples,
we find logarithmic gain coefficients of up to 45 cm-1 with time constants for the build-up of the purely π/2-shifted refractive index grating of the order of 1 ms for the blue
lines of an Ar+ laser. Photoconductivity depends nonlinearly on light intensity with an exponent x≈0.55. With increasing implanted helium
dose, both electronic and nuclear damage of the waveguiding layer grows, and the photorefractive properties of the waveguides
are considerably degraded.
Received: 20 February 1997/Revised version: 1 May 1997 相似文献
7.
V. Sivakumar Arunachalam Lakshmanan S. Kalpana R. Sangeetha Rani R. Satheesh Kumar M.T. Jose 《Journal of luminescence》2012,132(8):1917-1920
Zn2SiO4:Mn green phosphor having comparable photoluminescence (PL) efficiency with commercial phosphor has been synthesized at 1000 °C using solid state reactions involving ZnO, silicic acid and manganese acetate. The water of crystallization attached to SiO2 in silicic acid whose dissociation at 1000 °C seem to promote the sintering efficiency of Zn2SiO4:Mn. Incremental ZnO addition and re-firing at 1000 °C promote the diffusion rate of ZnO and SiO2. The formation of a single crystalline phase of willemite structure in the samples was confirmed by powder XRD measurements. The phosphor exhibit an intense excitation band centered around 275 nm and a relatively weak excitation centered around 380 nm while the broad band green emission peaks at 524 nm. Other parameters studied include PL spectra, grain morphology, ZnO/SiO2 molar ratio, Mn concentration, co-dopant/flux and the effect of chemical forms of Mn dopant as well as silica on the PL efficiency. 相似文献
8.
9.
采用溶胶-凝胶法在Zn2SiO4基质中掺杂Eu3+,合成了红色荧光粉Zn2SiO4:Eu3+.通过样品的X射线衍射光谱、红外光谱、扫描电镜以及光致发光光谱的测试和表征,研究了Zn2SiO4:Eu3+的内部结构和发光特性.扣描电镜结果显示样品为球状荧光粉,颗粒直径为1~3μm.在395 nm激发下,样品在613 nm处发射出很强的红光.结合荧光光谱,分析了样品的退火温度,Eu3+的浓度,电荷补偿剂Li+的浓度对样品发光强度的影响.研究发现,红色荧光粉Zn2SiO4:Eu3+的发光强度随退火温度的升高而增加,发光强度随Eu3+和Li+浓度的增加先增大后减小. 相似文献
10.
jet =18600). Here, PLIF images reveal a CH layer of thickness typically <1 mm from flame base to tip. Furthermore, in these permanently
blue flames, we observe instantaneous flamefront strain rates – derived from the PIV data – in excess of ±104 s-1 without flame extinction.
Received: 16 October 1997/Revised version: 30 October 1997 相似文献
11.
采用溶胶-凝胶法制备了Zn2SiO4:Mn薄膜并结合毛细管微模板技术实现了薄膜的图案化,利用X射线衍射(XRD),原子力显微镜,光学显微镜,发光光谱等手段对Zn2SiO4:Mn的结晶过程、发光性质进行了研究.XRD结果表明,溶胶-凝胶法合成的样品在800℃时已开始结晶,在1000℃时可得到纯相的Zn2SiO4:Mn,这比传统的固相法的烧结温度低150℃.Zn2SiO4:Mn薄膜的激发光谱在220nm和280nm之间有一个强的吸收峰,峰值位于248nm,发射光谱的最大值位于522nm,为绿光发射.从原子力显微镜照片可知组成薄膜的粒子比较均匀,其平均直径为220nm.我们获得了四种图案化宽度,分别是5,10,20,50μm.光学显微镜的结果表明,图案薄膜烧结后相对于烧结前有10%~20%的收缩. 相似文献
12.
Green-light-emitting Zn2SiO4:Mn phosphor particles were synthesized by modified large-scale spray pyrolysis using a colloidal solution containing fumed silica particles. The particles had a fine size, filled morphology, spherical shape and non-aggregation characteristics even after post-treatment at 1150 °C. The luminescence characteristics of Zn2SiO4:Mn phosphor particles having spherical shape, such as brightness and decay time under VUV excitation light, were investigated as a function of Mn content. The luminescence intensity exhibits a maximum at 5 mol% Mn-doped powder. The decay time increases consistently with decreasing Mn content and more saturated color coordinates are obtained with the composition having 12 mol% Mn. As a consequence, the 10 mol% Mn-doped powder proved to provide a good combination of favorable luminance and acceptable decay time. The influence of post-treatment temperature on the decay time and photoluminescence characteristics of Zn2SiO4:Mn particles was also investigated. Particles post-treated at 1155 °C had the maximum photoluminescence intensity, which was identical to 113% that of the commercial product, and a comparable decay time of 5.8 ms. PACS 81.20.Rg; 78. 55.Hx; 78.40.Ha; 81.05.Hd; 81.40.Tv 相似文献
13.
Zn2 SiO4:Mn,Cd磷光体的长余辉特性 总被引:1,自引:0,他引:1
高温固相法合成Zn2SiO4:1.2%Mn,5%Cd长余辉磷光体,对样品进行了X射线衍射分析、光谱分析以及余辉衰减特性测量。分析结果表明,在1050℃下烧结3h的硅酸锌产物为单相。Zn2SiO4:1.2%Mn,5%CdK余辉磷光体在243nm或260nm激发下,发射光谱最大峰值位于521nm处,其色坐标x=0.2301,Y=0.69150在254nm紫外光激发5min后样品的余辉发光在暗室里可持续观察的时间约为1h,与Zn2SiO4:1.2%Mn磷光体比较,显示了更好的余辉特性。 相似文献
14.
采用水热合成方法添加KOH在SiO2颗粒表面包覆Mn2+掺杂纳米Zn2SiO4,通过X射线衍射(XRD)仪、扫描电子显微镜(SEM)、能谱、光致发光(PL)光谱仪对产物的晶体结构、形貌及光学性能进行表征,并对Zn2SiO4晶体在水热反应过程中的反应机制进行了讨论。XRD测试结果表明:220℃水热条件下,添加少量KOH,反应不同时间后,可在石英砂表面生成一层Zn2SiO4;SEM照片显示所生成的Zn2SiO4为六棱柱形,并且不同反应条件下Zn2SiO4的包覆程度不同。反应产物经光致发光性能研究表明:Mn2+掺杂纳米Zn2SiO4包覆SiO2样品中显示两套光致发光谱,一套为250nm左右激发产生的522nm绿色发光带,另一套为340~410nm宽带激发的440nm蓝色发光带,前者为典型的Mn2+离子发光,后者440nm发光带则有可能来源于基体SiO2的氧空位缺陷。 相似文献
15.
16.
Onufrieva T. A. Krasnenko T. I. Zaitseva N. A. Baklanova I. V. Rotermel’ M. V. Ivanova I. V. Popov I. D. Samigullina R. F. 《Physics of the Solid State》2019,61(5):806-810
Physics of the Solid State - The analysis of the unified series of single-phase Zn2 – 2xMn2xSiO4 samples (x ≤ 0.2) has provided the possibility to determine the... 相似文献
17.
H. Strausky J.R. Krenn A. Leitner F.R. Aussenegg 《Applied physics. B, Lasers and optics》1998,66(5):599-602
Received: 28 July 1997/Revised version: 20 October 1997 相似文献
18.
Zn2SiO4:Mn2+荧光粉的燃烧法合成及其发光特性 总被引:2,自引:2,他引:2
用燃烧法成功合成了Zn2-xsiO4:xMn(0≤x≤0.10)粉末样品并表征了其发光特性.XRD测量结果表明,在600℃下燃烧数分钟、900℃以上进行热处理4 h后,所得样品为单相Zn2-xSiO4:xMn(0≤χ≤0.10,Willemite).监控525 nm发射,测得Zn2-xSiO4:xMn(0<χ≤0.10)的最强激发峰为Mn2+的6A1→4T1跃迁(约254 nm).254 nm激发下,Zn2-xSiO4:xMn(0<χ≤0.10)的最强发射峰为Mn2+的3d电子组态内自旋禁戒的4Ti→6AJ跃迁(约525 nm).结果表明,发光强度、最强峰位、最佳激活剂浓度等与初始原料、燃烧温度、燃烧剂的用量、粉末粒度等有关. 相似文献
19.
Mufei Xiao 《Applied Physics A: Materials Science & Processing》1996,64(1):91-99
Within the framework of electric dipole approximation, the focused light spot produced by a tiny optical fiber tip in front
of a phase conjugate mirror is investigated numerically. The fiber tip is the probe of a reflection scanning near field optical
microscope and the incident light is guided through the fiber. Intensity distribution of local field is calculated in the
half space where the fiber tip locates. Both homogeneous (q
‖≤ω/c
0) and part of inhomogeneous (ω/c
0<q
‖≤ωn/c
0) fields are included in establishing a field propagator (Green’s function) which is employed to calculate the local field
distribution. The local field forms at the tip position a diffraction light spot with a finite central value and a finite
size, and when the tip-surface distance is sufficient small, the strength and the shape of the light spot become a function
of the distance, which is due to the contribution of evanescent field. Fairly good agreements are found with the existing
experimental reports.
Received: 30 April 1996/Accepted: 19 August 1996 相似文献