Colour centres and thermally stimulated luminescence of Na2ZnCl4

Thermally stimulated luminescence (TSL) of Na₂ZnCl₄ single crystals showed three glow peaks having their peak maxima at 343, 425 and 475 K. Optical absorption (OA) data of unirradiated samples revealed an absorption band at 272 nm while X-irradiation caused additional bands at 462 and 723 nm. Growth and room temperature annealing studies of TSL and OA supported the idea of attribution of 425 K glow peak and 462 nm absorption band to F-centres. The 272 nm OA band is due to Zn²⁺ centres whereas the 723 nm absorption band and 475 K glow peak have been assigned to Zn⁺ centres.     

A new effective thermoluminescent material: LiCaAlF6:Ce

Absorption, emission and thermostimulated luminescence (TSL) of as-grown and X ray irradiated pure and Ce-doped LiCaAlF6 crystals were investigated. Ce-containing samples demonstrate intensive TSL in the UV region (280-310 nm) with a main peak at 350 degrees C. It is found that the well known UV laser crystal LiCaAlF6:Ce is a promising thermoluminescent dosemetric material.     

Thermoluminescence of MgSO4 doped with Eu and P impurities

CaSO4:Eu, MgSO4:Eu and MgSO4:Eu,P phosphors have been prepared and their thermoluminescence (TL) characteristics were studied. A main glow peak due to Eu2+ ions is seen at approximately 146 degrees C and 440 nm and glow peaks at approximately 145 degrees C, approximately 190 degrees C, approximately 260 degrees C and approximately 360 degrees C for 590 nm and 625 nm wavelengths are identified as Eu3+ ion emissions in MgSO4:Eu. Emission spectra in MgSO4:Eu and the MgSO4:Eu,P show that the MgSO4:Eu3+ glow peak at 260 degrees C for 590 nm and 625 nm shifts to 280 degrees C with enhanced intensity while the Eu2+ ion glow peak at 146 degrees C remains but with reduced intensity. The main glow peak at approximately 146 degrees C and 440 nm from Eu2+ ions shows significant difference from the characteristic glow peaks of Eu3+ ions. It is observed that the wavelength of the Eu2+ ion glow peak is inversely proportional to the radius of the cation of the host sulphate in alkaline-earth sulphate phosphors. By contrast the wavelengths of the Eu3+ ion glow peaks remain unchanged in different sulphates. Besides, the glow curve at approximately 146 degrees C obtained using a conventional blue sensitive reader shows simply the first order kinetics. It is concluded that the luminescence centres and distribution of traps related to Eu2+ ions are different from that of Eu3+ ions in MgSO4:Eu and MgSO4:Eu,P phosphors.     

Dosimeter properties of CaO transparent ceramic prepared by the SPS method

We have studied photoluminescence (PL), scintillation and thermally-stimulated luminescence (TSL) dosimeter properties of CaO transparent ceramic, in comparison with those of MgO transparent ceramic as a reference. Both samples were made by a Spark Plasma Sintering method. In the PL spectra, both samples showed emission peaks due to F and F⁺ centers. Moreover, in addition to these peaks, a scintillation emission peak was detected at 330 nm for both CaO and MgO, which was caused by surface defects. The TSL glow curves showed a main peak around 55 °C for CaO and 140 °C for MgO. The TSL response was confirmed to monotonically increase with irradiation dose over the dose range from 0.1 to 1000 mGy.     

Fluorescence spectrum of 2-trifluoromethyl-1,1,1,2,4,4,5,5,5-nonafluoro-3-pentanone

A perfluorinated ketone, 2-trifluoromethyl-1,1,1,2,4,4,5,5,5-nonafluoro-3-pentanone, has been investigated to determine several physical and spectroscopic properties. It was found to exhibit fluorescence similar to that of acetone, emitting over the 360-550 nm range with a peak near 420 nm when excited at 355 nm. This compound's emission is nearly unaffected over a wide range of temperature and pressure in an argon bath gas. Its fluorescence efficiency was found to be three times higher than that of acetone. Combined with low reactivity and thermal stability up to 500 degrees C, this makes the material an excellent tracer for spectroscopic measurement techniques.     

ZnO nanoparticles embedded in sapphire fabricated by ion implantation and annealing

ZnO nanoparticles were fabricated in sapphire (α-Al(2)O(3) single crystal) by Zn ion implantation (48?keV) at an ion fluence of 1 × 10(17)?cm(-2) and subsequent thermal annealing in a flowing oxygen atmosphere. Transmission electron microscopy (TEM) analysis revealed that metallic Zn nanoparticles of 3-10?nm in dimensions formed in the as-implanted sample and that ZnO nanoparticles of 10-12?nm in dimensions formed after annealing at 600?°C. A broad absorption band, peaked at 280?nm, appeared in the as-implanted crystal, due to surface plasma resonance (SPR) absorption of metallic Zn nanoparticles. After annealing at 600?°C, ZnO nanoparticles resulted in an exciton absorption peak at 360?nm. The photoluminescence (PL) of the as-implanted sample was very weak when using a He-Cd 325?nm line as the excitation source. However, two emission peaks appeared in the PL spectrum of ZnO nanopraticles, i.e., one ultraviolet (UV) peak at 370?nm and the other a green peak at 500?nm. The emission at 500?nm is stronger and has potential applications in green/blue light-emitting devices.     

High coercivity of ordered macroporous FePt films synthesized via colloidal templates

The preparation of a three-dimensionally (3D) ordered macroporous iron-platinum (FePt) film derived from monodisperse FePt nanoparticles (approximately 3 nm in diameter) and polystyrene latex particles (254 nm in diameter) is described. The prepared film has a hexagonally ordered porous structure and coercivity up to 10 kOe after annealing at a temperature of 600 degrees C. We also found that size of FePt particles was maintained at around 3 nm, even after annealing at a temperature of 600 degrees C.     

Defect centres and thermoluminescence in CaSO4:Dy,Ag phosphor

The defect centres formed in the TL phosphor CaSO4:Dy,Ag are studied using the technique of Electron Spin Resonance. The Ag co-doped phosphor exhibits three glow peaks around 130, 220 and 375 degrees C in contrast with the two glow peaks observed in the CaSO4:Dy phosphor at 130 and 220 degrees C at a gamma ray dose of 1Gy. ESR studies show that the additional peak at 375 degrees C correlates with a Ag2+ centre formed due to gamma irradiation and observable only below -170 degrees C. The Ag2+ centre is characterised by an axial g-tensor with principal values g(parallel) = 2.38 and g(perpendicular) = 2.41. ESR studies further indicate that the precursor to a centre observable at low temperature (-170 degrees C) appears to act as the recombination centre for the TL peak at 375 degrees C; this radical is characterised by the g-values g(parallel) = 2.0023 and g(perpendicular) = 2.0038 and is assigned to SO3- radical. It is observed that there is more incorporation of Ag in the CaSO4:Dy system as compared with that in pure CaSO4 system.     

Solution grown nanocrystalline ZnO thin films for UV emission and LPG sensing

Nanocrystalline ZnO thin films were successfully deposited by a simple and inexpensive solution growth technique. Photoluminescence (PL) and liquefied petroleum gas (LPG) sensing properties were investigated. Films were found to be uniform, pinhole free, and well adherent. As deposited and heat treated (at 673 K for 2 h) films were characterized by XRD, SEM, and EDAX. The dc electrical resistivity and LPG sensing property were measured. The change in morphology, from spherical particle to rod-like, was observed after air annealing. XRD results revealed that the obtained films were nanocrystalline and had a hexagonal wurtzite structure. The absorption edge was found to be at around 366 nm for the as-deposited film and 374 nm for the annealed film. The band gaps were found to be 3.29 and 2.9 eV for the as-deposited and annealed films, respectively. PL spectra of ZnO thin films showed strong peak at 384 nm, which corresponds to near band edge emission (UV emission) and a relatively weak peak at 471 nm. Further, the annealed film was used for detection of LPG in air. Maximum response was observed at 673 K. The maximum sensitivity of sensor was found to be 4.5 for 0.6 vol.% LPG. Sensing response got saturated after 0.6 vol.% of gas concentration. A possible mechanism of LPG sensing has been explained.     

Nanostructure of pure iron anodically oxidized in borate buffer solution and annealed by infrared radiation

The behavior of oxide film on pure iron passivated in a borate buffer solution and subsequently radiated by infrared light (IR) was investigated in comparing to that by just IR annealing without passivation, and was evaluated by film structure, etc. The effect of thermal annealing over 250 degrees C was observed with gamma-Fe2O3 grain growth and sharp increase in surface roughness, film thickness and oxygen content. An ellipsometric parameter of tan psi was sensitively reflected by annealing effect, and tan psi curve had a shoulder at 150 degrees C for 5 min and a peak of tan psi was shifted from 350 nm to 450 nm in wavelength. This shift was also caused by the formation of gamma-Fe2O3, because the peak was also observed in tan psi of the bulk Fe2O3 family. Passivation effects at 800 mV prior to IR annealing on thickness and oxygen content changed at 150 degrees C, and decreased tan psi at 350 nm and excessive film growth over 250 degrees C, and increased oxygen content under 100 degrees C and surface roughness at 50-250 degrees C. The terrace width with atomic scale flatness was slightly increase by passivation prior to IR annealing at 50-250 degrees C, and the maximum terrace width reached larger than 10 nm by passivation and IR annealing at 100 degrees C for 30 min.     

Band analysis of temperature-dependent near-infrared spectra of oleic acid in the pure liquid state by the analytic geometric approach

The applicability of the band-stripping and complementary matching method has been demonstrated by the analysis of temperature-dependent near-infrared (NIR) absorption spectra in the 7500-6500 cm(-1) region of oleic acid (cis-9-octadecenoic acid) in the pure liquid state. This method is based on first derivative-second derivative pair (D1-D2) plots and a new concept called the complementary band, cBDi, created by subtracting all the rest of the bands, exclusive of the ith estimated band, eBDi, from an experimental spectrum. The degree of coincidence of both band shapes provides a suitable measure for the quality of fit for each individual component band. It has been confirmed from the present analysis of the NIR spectra of oleic acid measured over a temperature range of 16-79 degrees C that the change of the peak intensity of the component band at around 6915 cm(-1) due to the first overtone of an O-H stretching vibration of the monomer has two transition points around 35 and 55 degrees C. Moreover, the present study has provided new insight into the analysis of temperature-dependent spectral variations of oleic acid. Among the three temperature ranges, 16-35 degrees C, 35-55 degrees C, and 55-79 degrees C, in the first range the band near 6915 cm(-1) shows a slight increase and in the second range it has a linear intensity change with a slope of 0.002 a.u./degree C. In the third range, a rapid increase of the peak intensity is observed. This band exists even at 15 degrees C (just below the melting point) and shows a shift from 6910 to 6915 cm(-1) and a band narrowing from 85 to 80 cm(-1) (full width at half-height) over a temperature range of 16 to 79 degrees C. Furthermore, it has been found that there are two broad bands at around 6835 and 6778.     

The influence of post-exposure heating on the stability of MCP-N (LiF:Mg,Cu,P) TL detectors

Post-exposure annealing of highly sensitive LiF:Mg,Cu,P (MCP-N) detectors, at 100 degrees C over 10 or 20 min prior to readout, is usually recommended for routine dosimetry. The purpose of this anneal is to eliminate low-temperature peaks, especially peak 3, which fades at room temperature in about 3 months. However, as this annealing procedure does not entirely eliminate peak 3, 10% of its thermoluminescent (TL) signal still being readable, a fading correction must be applied. The aim of this work was to optimise the conditions of post-exposure treatment, i.e. its temperature and duration, in order to facilitate the use of MCP-N detectors in routine dosimetry. MCP-N detectors were annealed in standard conditions, i.e. at 240 degrees C over 10 min and exposed to a dose of 5 mGy (137Cs). For post-exposure annealing, six different temperatures between 100 degrees C and 150 degrees C and two time periods (10 and 20 min) were tested. TL glow curves were deconvoluted with the GCA code. A post-exposure anneal at 120 degrees C over 10 min was found to be optimal. Heating at this temperature eliminates 100% of the TL signal of peak 3, while maintaining the area and maximum intensity of the main peak 4 unchanged. In this case, no fading correction needs to be applied. Annealing at higher temperatures, up to 150 degrees C, results in a loss of peak 4 signal, and is therefore not recommended.     

Design of low cost gas sensor based on SrTiO3 and BaTiO3 films

We have prepared SrTiO3/BaTiO3 multilayer film on alumina substrates by a sol-gel technique and investigated their response for sensing ethanol vapor. The surface morphology of the films were characterized by atomic force microscope (AFM) showing that the grain size of the films increase up to 40 nm as the annealing temperature increased to 1000 degrees C. The ethanol sensors based on SrTiO3/BaTiO3 thin films were fabricated by applying interdigitated gold electrodes by sputtering technique. The ethanol sensing characteristics of SrTiO3/BaTiO3 thin films were quantified by the change in resistance of the sensors when they were exposed to ethanol. The optimum operating tempearature of these sensors was found to be 350 degrees C. In addition, the film annealed at 1000 degrees C exhibited p-type gas sensing behavior with the best sensitivity of 30-100 for low ethanol concentration in the range of 100-1000 ppm.     

Glow curves and the emission of flux-grown BaFCl:Na crystals

The thermoluminescence glow curves and the emission spectra of flux-grown BaFCl:Na crystals were recorded. An additional TL peak at 320 K, an optical absorption band at 570 nm and an emission peak at 490 nm have been seen in X/-irradiated crystals. Bleaching, room-temperature annealing and high-temperature emission results led us to conclude that the sodium impurity is responsible for the additional glow peak, optical absorption band and emission peak.     

甘氨酸燃烧法合成Sr2CeO4及其发光性质研究

为制备具有优良性能的蓝色荧光粉,首次采用甘氨酸-硝酸盐燃烧法合成了Sr2CeO4,利用热重-差热分析仪、X射线粉末衍射仪、扫描电镜等技术对其形成过程、物相结构、形貌粒度、发光性质进行了研究.结果表明:燃烧后的前驱物经800℃焙烧已有目标产物Sr2CeO4生成,1100℃时可得到较纯正交晶系的Sr2CeO4相.颗粒的形貌为不规则球形,平均粒径在80 nm左右.发光性质研究表明:Sr2CeO4荧光粉的激发光谱是宽带双峰结构,此宽带属于Ce4+的电荷迁移带,两个峰分别位于305 nm和348 nm,后者为主峰.用348 nm紫外光激发样品,发出明亮的蓝光,其发射光谱也是一个宽带,最大峰位于470 nm,此峰属于Ce4+的f→t1g跃迁.发光强度在800~1100℃随温度升高而增强.     

Thermally stimulated luminescence and photoluminescence investigations of Eu3+ and Eu2+ doped SrBPO5

Thermally stimulated luminescence (TSL) investigations of SrBPO₅:Eu^3?+ and SrBPO₅:Eu^2?+ phosphors were carried out in the temperature range of 300–650 K. In order to characterize the phosphors, X-ray diffraction and photoluminescence (PL) techniques were used. The emission spectrum of air heated SrBPO₅:Eu^3?+ phosphor exhibited emission bands at 590, 614, 651 and 702 nm under 248 nm excitation, assigned to transitions of Eu^3?+ ion. In phosphor prepared in reducing (Ar + 8% H₂) atmosphere, a broad emission band due to Eu^2?+ ranging from 350 to 400 nm was observed with 340 nm excitation. EPR studies have confirmed the presence of Eu^2?+ ions in the samples prepared in reducing atmosphere. TSL glow curve of SrBPO₅:Eu^3?+ had shown intense peaks around 397, 510, 547 K and a weak peak around 440 K whereas in case of SrBPO₅:Eu^2?+ system, glow peaks at 414, 478 and weak peak at 516 nm were observed. The shift in TSL glow pattern can be attributed to stabilization of different oxidation states of the dopant ion in the host lattice. Apart from this, TSL trap parameters such as trap depth and frequency factor were determined. Spectral characteristics of TSL emission have shown that Eu^3?+?/Eu^2?+ ion acts as the luminescent centre in the respective phosphors.     

Pr3+掺杂对SrAl2O4:Eu2+、Dy3+磷光体发光性能的影响

用燃烧法制备Pr~(3+)掺杂的SrAl_2O_4:Eu~(2+)、Dy~(3+)长余辉发光粉体,研究了Pr~(3+)掺杂对其发光性能的影响。结果表明,合成的单相SrAl_2O_4样品具有单斜晶系结构,荧光发射光谱是连续宽带谱,峰位于515 nm,激发光谱是峰值在320 nm和360 nm的连续宽带谱。掺杂Pr~(3+)对形成晶粒尺寸均匀的固溶体有一定的促进作用,使其余辉初始亮度为不掺杂时的3倍。     

Thermoluminescence properties of LiF:Mg,Cu,Na,Si pellets in radiation dosimetry

Sintered LiF:Mg,Cu,Na,Si thermoluminescence (TL) pellets have been developed for application in radiation dosimetry. LiF:M,Cu,Na,Si TL pellets were made from TL powders using a sintering process, that is, pressing and heat treatment. These pellets have a diameter of 4.5 mm, and a thickness of 0.8 mm are blue in colour and have a mass of 28 mg each. After 400 pellets had been produced they were irradiated with 137Cs gamma radiation and samples having a sensitivity within a +/-5% standard deviation were selected for experimental use. In the present study, the physical and dosimetric properties of LiF:Mg,Cu,Na,Si TL pellets were investigated for their emission spectrum, dose response, energy response and fading characteristics. Photon irradiation for the experiments was carried out using X ray beams and a 137Cs gamma source at the Korea Atomic Energy Research Institute (KAERI). The average energies and the dose were in the range of 20-662 keV and 10(-6) - 10(2) Gy respectively. The glow curves were measured with a manual type thermoluminescence dosimetry reader (system 310, Teledyne) at a constant nitrogen flux and a linear heating rate. For a constant heating rate of 5 degrees C.s(-1). the main dosimetric peak of the glow curve appeared at 234 degrees C, its activation energy was 2.34 eV and the frequency factor was 1.00 x 10(23). The TL emission spectrum appeared at the blue region centred at 410 nm. A linearity of photon dose response was maintained up to 100 Gy. The photon energy responses relative to the 137Cs response were within +/-20% in the overall photon energy region. No fading of the TL sensitivity of the pellets stored at room temperature was found over the course of a year. Therefore LiF:Mg,Cu,Na,Si TL pellets can be used for personal dosimetry, but more research is needed to improve the characteristics for repeated use.     

Effect of ion doping with donor and acceptor impurities on intensity and lifetime of photoluminescence from SiO2 films with silicon quantum dots

Doping with donor and acceptor impurities is an effective way to control light emission originated from quantum-size effect in Si nanocrystals. Combined measurements of photoluminescence intensity and kinetics give valuable information on mechanisms of the doping influence. Phosphorus, boron, and nitrogen were introduced by ion implantation into Si+ -implanted thermal SiO2 films either before or after synthesis of Si nanocrystals performed at Si excess of about 10 at.% and annealing temperatures of 1000 and 1100 degrees C. After the implantation of the impurity ions the samples were finally annealed at 1000 degrees C. It is found that, independently of ion kind, the ion irradiation (the first stage of the doping process) completely quenches the photoluminescence related to Si nanocrystals (peak at around 750 nm) and modifies visible luminescence of oxygen-deficient centers in the oxide matrix. The doping with phosphorus increases significantly intensity of the 750 nm photoluminescence excited by a pulse 337 nm laser for the annealing temperature of 1000 degrees C, while introduction of boron and nitrogen atoms reduces this emission for all the regimes used. In general, the effective lifetimes (ranging from 4 to 40 micros) of the 750 nm photoluminescence correlate with the photoluminescence intensity. Several factors such as radiation damage, influence of impurities on the nanocrystals formation, carrier-impurity interaction are discussed. The photoluminescence decay is dominated by the non-radiative processes due to formation or passivation of dangling bonds, whereas the intensity of photoluminescence (for excitation pulses much shorter than the photoluminescence decay) is mainly determined by the radiative lifetime. The influence of phosphorus doping on radiative recombination in Si quantum dots is analyzed theoretically.     

Sensitivity loss of Lif:Mg,Cu,P thermoluminescence dosemeters caused by oven annealing

LiF:Mg,Cu,P is a very sensitive thermoluminescence material that can be used for personal dosimetry in radiology. But if this material is heated too much during annealing or reading it quickly loses its sensitivity. This study shows that an annealing oven in wide use can cause thermal damage to the dosemeters owing to inhomogeneous temperature distribution in the annealing tray. At annealing temperatures>240 degrees C, differences of only 1 degrees C lead to significant losses of sensitivity. Therefore, it is necessary to measure the distribution of temperature in the annealing tray for correct placement of the dosemeters in the tray.