Synthesis of stable dispersion of ZnO quantum dots in aqueous medium showing visible emission from bluish green to yellow

Aqueous dispersion of 4-8 nm size stable ZnO quantum dots (QDs) exhibiting luminescence in the visible region have been synthesized by a simple solution growth technique at room temperature. Silica has been used as capping agent to control the particle size as well as to achieve uniform dispersion of QDs in aqueous medium. X-ray diffractometer (XRD) analysis reveals formation phase pure ZnO particles having wurzite (hexagonal) structure. Atomic force microscope (AFM) images show that the particles are spherical in shape, having average crystalline sizes ∼4, 5.5 and 8 nm for samples prepared at pH values of 10, 12 and 14, respectively. From the optical absorption studies, the band gap energy of QDs is found to be blue shifted as compared to bulk ZnO (3.36 eV) due to the quantum confinement effect and is consistent with the band gap calculated by using effective-mass approximation model. The photoluminescence (PL) observed in these QDs has been attributed to the presence of defect centers.     

Luminescence enhancement of Eu-doped calcium magnesium silicate blue phosphor for UV-LED application

(Ca_1−x,Eu_x)MgSi_2yO_6+δ blue phosphor was prepared by spray pyrolysis and the photoluminescence properties were optimized by controlling concentration of Si element and the activator content. At y=1.0, the concentration quenching in the luminescent intensity appeared when the Eu²⁺ content (x) was 0.01 (1 at%). Such quenching concentration was changed with the concentration of silicon (y), which was increased with an increase in the quantity of excess Si (y>1.0). The highest luminescent intensity was achieved when the Eu²⁺ content (x) and the Si concentration (y) were 0.04 and 1.3, respectively. According to X-ray diffraction (XRD) analysis, the tetragonal SiO₂ phase was formed as a minor phase when the y value was larger than 1.3. The formation of SiO₂ phase, however, did not reduce but increased the luminescent intensity when the Eu²⁺ content was optimized again. As a result, the luminescent intensity of the phosphor particles optimized in the content of both Si and Eu²⁺ was about 150% improved compared with that of the CaMgSi₂O₆:Eu sample (x=0.01, y=1.0).     

Time-resolved optical spectroscopy of CsI(Tl) crystals by pulsed electron beam irradiation

Properties of the color and emission centers induced with an electron pulse beam at temperature within 80-300 K have been studied in CsI(Tl) crystals. It has been established by optical spectrometry with time resolution that initial color centers in this crystal are only Tl⁰ and V_k centers, which spontaneously recombine emitting visible light at 2.25 and 2.55 eV. It has been shown that the emission decay kinetics at 80 K include two fast exponential components with decay constants 3 and 14 μs as well as slow hyperbolic component with the power index depending on the wavelength of the emitting light. The temperature effect on the emission kinetics has been studied and it has been directly proved that the emission rise stage at the temperature above 170 K is caused by the recombination of electrons, which are thermally released from single Tl⁰ centers, with V_kA centers. The origin of scintillations in CsI(Tl) crystal is discussed in terms of the tunnel electron transitions from ground state of Tl⁰ centers to ground state of V_k centers at different distances from each other.     

基于邻菲咯啉的反应型三元铕配合物的合成与荧光性质

以二苯甲酰甲烷(HDBM)为第一配体,5-丙烯酰胺基-1,10-菲咯啉(Aphen)为活性第二配体,制备了新的反应型三元铕配合物Eu(DBM)₃Aphen。通过元素分析、红外光谱和热分析对配合物进行了组成确定,采用紫外光谱、荧光光谱、荧光寿命和荧光量子产量研究了配合物的光物理性能。结果表明,在紫外光激发下,配合物Eu(DBM)₃Aphen能发射Eu3+的特征荧光,其荧光发射强度、单色性、荧光寿命和荧光量子产率等均显著高于文献报道的丙烯酸配合物Eu(DBM)₂AA的相应数值,表明配合物Eu(DBM)₃Aphen不仅可作为潜在的红色发光材料,还可作为反应型的配合物,为制备具有优异发光性能的稀土聚合物提供了一条新的途径。     

一种天然正长石的释光特性

应用RGB-3B型热释光仪和BG2003释光谱仪对一种正长石矿物的热释光和选频释光发光曲线进行测定,获得正长石的释光特性。研究表明：天然正长石的三个热释光峰峰温为148,197,310 ℃,辐照一定剂量后,出现197 ℃和263 ℃两个稳定的热释光峰。正长石的峰位温度随着增温速率的减小,向左移动。选频热释光290, 300, 310, 340, 400, 480 nm存在释光响应,选频绿光释光280, 290, 300, 310, 320, 400, 460, 480 nm存在释光响应,400 nm频道的光子计数随剂量的变化具有一定的线性关系,具有辐射剂量计的特性,具备释光测年的应用潜力。     

La2Zr2O7:Eu3+纳米棒的合成、表征及其荧光性能

采用传统固相法和水热法成功地制备出棒状La₂Zr₂O₇:Eu³⁺荧光粉. 利用X射线粉末衍射仪、透射电镜和荧光光谱仪等分析了产物的结构、形貌和发光特性. 结果表明红色荧光粉La₂Zr₂O₇:Eu³⁺有良好的晶相,属于立方结构,空间点群为Fd3m; 其形貌主要为纳米棒, 平均直径约47 nm, 长度为50～700 nm. 并对纳米棒的生长机理进行了探讨. 在466 nm蓝光激发下,La₂Zr₂O₇:Eu³⁺荧光粉能发射出Eu³⁺的特征红色荧光,发射主峰位于616 nm处,归属于Eu³⁺的⁵DO_→⁷F2_{超灵敏电偶极跃迁.此外,在产物的发射光谱中能够观察到⁵D}1_→⁷FJ _{(J=0, 1, 2)跃迁和⁵D}1_→⁷FJ _{(J=1, 2, 4)跃迁的劈裂峰,这说明Eu³⁺处在低对称性的晶体场格位中.}     

Sediment dating by luminescence: a review

In the present article we review applications of luminescence methods for the determination of the age of sediments for Quaternary Earth science. “Sediment” is taken to include any mineral particles transported by wind, water and/or ice and subsequently deposited. Methodology is not discussed per se but appears in context. The emphasis is on recent work and is illustrative rather than exhaustive. Applications in archaeology are mentioned only briefly. Successful dating requires that the luminescence signal has been zeroed by sunlight at the time the sediment was laid down. Dune sands and loess transported in full daylight usually satisfy this condition and have been dated by both traditional thermoluminescence and by optical methods. Optical dating is advantageous for less well-bleached sediments, such as are found in colder climates and those laid down by fluvial and glacial processes, although the prospects for dating the latter are shown to be poor. Among less common contexts are volcanic eruptions, earthquake faults and tsunami deposits. The dating of very young sediments, less than 2 ka, is demonstrated and the factors limiting the dating of very old sediments, 500 ka to 1 Ma, are discussed. Validation of any dating method by comparison with other methods is necessary; luminescence ages have been successfully compared with ages obtained by, for example, ¹⁴C, U–Th series and δ¹⁸O isotope ratios. The most difficult problems encountered in dating quartz, feldspars and undifferentiated fine grain mixtures include: anomalous fading (which leads to underestimates of age), incomplete zeroing (which gives overestimates) and sample inhomogeneity. Methods devised to minimise these effects include preheating regimes, selection of observing wavelengths and of stimulating wavelengths for optical dating, the use of single aliquot and single grain measurements. The use of appropriate data analysis procedures is also important. Advice on current best practice on procedures for obtaining reliable ages is offered and, in all applications, there are suggestions as to where further research might be directed.     

Optical activity and damage recovery of erbium implanted strontium titanate

Single crystalline SrTiO 3 samples were implanted with Er ions of 150 v keV at room temperature with fluences of 5 ‐ 10 14 and 5 ‐ 10 15 . Annealing treatments were carried out both in reducing and oxidising atmospheres to recover the implantation damage. Infrared 1.54 v m Er 3+ luminescence between the two lowest spin-orbit levels 4 I 13/2 M 4 I 15/2 as well as emission from higher excited states 4 S 3/2 M 4 I 15/2 , 4 F 9/2 M 4 I 15/2 and 4 S 3/2 M 4 I 13/2 were observed in the implanted samples with highest fluence, annealed either in air or in vacuum. Multiple site location of Er 3+ ion is discussed and compared with RBS/C and emission channelling results that indicate that Er goes to Sr and Ti sites.     

Europium-doped nanocrystalline Y2O3−La2O3 solid solutions with bixbyite structure

Nanocrystals of Y₂O₃ and La₂O₃ solid solutions were synthesized with a cubic bixbyite structure containing La₂O₃ content of up to 50 mol%. This is comparatively higher than that in bulk materials of the same structure, where La₂O₃ content of only 20 mol% can be obtained. A set of europium-doped (Y_1−xLa_x)₂O₃ (x=0.1, 0.2, 0.3, 0.4) cubic bixbyite solid solutions with crystallites of approximately 10 nm in size was prepared using the polymer complex solution method. Structural analysis was performed using X-ray diffraction measurements, Rietveld full profile refinement, and from Eu³⁺ luminescence emission. The energy levels of the Eu³⁺ ion, second order crystal field parameters, and crystal field strength were obtained for all compositions of solid solutions. We show that the crystal field parameters linearly depend on unit cell parameter and that these dependencies may be considered as part of an overall dependence for the entire sesquioxide family.     

Optical properties of surface-modified Bi2O3 nanoparticles

Stearic acid coated Bi₂O₃ nanoparticles in the size range of 5-13 nm were synthesized by the microemulsion method. HRTEM showed that the morphology of Bi₂O₃ nanoparticles was ellipsoidal. The absorption edge of Bi₂O₃ nanoparticles showed a blue shift of ∼0.45 eV, comparing with that of the bulk Bi₂O₃. At room temperature, Bi₂O₃ nanoparticles also showed a strong luminescence at 397 and 420 nm, depending on the excitation wavelength.