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1.
In the hexaaluminate laser material La0.9Nd0.1MgAl11O19 also known as LMA:Nd the Nd3+ fluorescence can be enhanced by codoping the matrix with rare-earth (REn+) or transition metal (TMm+) ions. A large number of potential donor ions D (D = Mn2+, Dy3+, Tb3+, Eu2+, Eu3+ and Ti3+) are studied in the hexaaluminate host. The D→Nd3+ energy transfer, t he, luminescent efficiency as well as the back-transfer strongly depend on the overlap of the D emission and Nd3+ absorption, the concentration of the two ions and their localization in the crystal host. In this paper the optical properties — absorption and emission — of the D and Nd3+ ions as well as the D→Nd3+ interactions are considered using a Forster-Dexter's approach, to compare the capabilities of the different donors in the Nd3+-doped hexaaluminate host. The CDNd and R0 parameters are estimated in each case, and the results discussed in terms of the localization of the donor ions, their absorption and emission as well as their lifetime properties. 相似文献
2.
Guocong Liu Xuechen Duan Haibin Li Dawen Liang 《Materials Chemistry and Physics》2008,110(2-3):206-211
GaOOH:Eu3+ nanorods with different aspect ratios were prepared by hydrothermal method at 140 °C. - and β-Ga2O3:Eu3+ were converted from as-prepared GaOOH:Eu3+ particles by calcination at 500 and 850 °C, respectively. The products were characterized with X-ray diffraction (XRD), transmission electron microscope (TEM) and photoluminescence (PL). Results show that solution pH values play a key role in the formation of the GaOOH:Eu3+ powders with different morphologies and - and β-Ga2:Eu3+ inherit the morphology of GaOOH:Eu3+ exactly. The photoluminescence characteristics of β-Ga2O3:Eu3+ were also investigated. Experimental results reveal that the color purity of β-Ga2O3:Eu3+ nanorods with high aspect ratio is enhanced in comparison with β-Ga2O3:Eu3+ nanorods with low aspect ratio. 相似文献
3.
采用高温固相反应法合成Sr2-x-yB5O9Cl:xEu2+,yTb3+蓝色荧光粉。用X射线衍射表征材料的晶体结构、用荧光光谱仪测定Eu2+和Tb3+的掺杂浓度,研究了助溶剂H3BO3过量浓度和反应温度对荧光粉发光性质的影响。结果表明,单掺杂Eu2+时,其浓度猝灭机理为电偶极-电偶极交互作用机制,浓度猝灭临界距离为RC=1.71 nm。在紫外(230-410 nm)波段有强而宽的吸收带,表明此粉是一种近紫外白光LED用的蓝色荧光粉。 相似文献
4.
Glasses of various compositions in the system (100 − x)(Li2B4O7) − x(SrO–Bi2O3–0.7Nb2O5–0.3V2O5) (10 x 60, in molar ratio) were prepared by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Glass composites comprising strontium bismuth niobate doped with vanadium (SrBi2(Nb0.7V0.3)2O9−δ (SBVN)) nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat-treated at 783 K/6 h) confirm the presence of rod shaped crystallites of SBVN embedded in Li2B4O7 glass matrix. The optical transmission spectra of these glasses and glass nanocrystal composites of various compositions were recorded in the wavelength range 190–900 nm. Various optical parameters such as optical band gap (Eopt), Urbach energy (ΔE), refractive index (n), optical dielectric constant and ratio of carrier concentration to the effective mass (N/m*) were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied. 相似文献
5.
Lithium has been inserted into, and extracted from, the spinel Li1.0V2O4 both electrochemically and chemically. Electrochemical and structural data show that in the system Li1+xV2O4, for 0 < x ≤ 0.5, Li+ ions are inserted into the interstitial octahedral sites of the Atet[B2]octX4 spinel structure. At x ≈ 0.5, Li+ ions in the tetrahedral A-sites are displaced into the remaining octahedral sites to yield, at x = 1, a rocksalt phase Li2V2O4; the [B2]X4 framework is unperturbed by the lithiation process. This framework also remains intact when Li+ ions are removed from Li1.0V2O4 to a composition Li0.67V2O4. Further extraction of lithium from the structure is accompanied by migration of some vanadium ions from the B-sites to the interstitial octahedral sites of the spinel structure. This process reduces the crystal symmetry from cubic to trigonal symmetry. In Li0.27V2O4 the structure resembles that of Li0.22VO2, obtained by delithiation of layered LiVO2, in which the vanadium cations are distributed in a 2:1 ratio between alternate cubic-close-packed oxygen layers; in the LiV2O4 spinel this ratio is 3:1. 相似文献
6.
This paper reports the preparation process and the long lasting phosphorescence of the Sr4Al14O25:Eu2+,Dy3+ thin films obtained by magnetron sputtering. Phosphorescence was achieved by annealing the films in reducing atmosphere. Sr4Al14O25 thin film was obtained when the films were treated at 1200 °C, while SrAl2O4 was generated as the intermediate phase during the annealing process. Sr4Al14O25:Eu2+,Dy3+ film generated an emission at 485 nm, and SrAl2O4:Eu2+,Dy3+ film showed an emission peaking at 515 nm. Afterglow characteristics were observed for both films, and Sr4Al14O25:Eu2+,Dy3+ film showed a better afterglow property than the SrAl2O4:Eu2+,Dy3+ film due to a deeper trap level and a higher trap concentration formed in the thin films. 相似文献
7.
Rate equations formalism is used to predict the population ratio of the Er3+ 4I13/2 levels involved in the 1.55 μm laser transition in the Yb:Er:CAS laser materials. An effective Yb → Er energy transfer, favourable to the Er3+ 1.55 μm laser emission, is demonstrated in this laser host. Indeed, the Yb → Er transfer and the Er → Yb back transfer rates are calculated to be 6 x 10−16 and 0.45 x 10−16 cm3 s−1, respectively. Attempts of codoping the system with Nd3+, Eu3+ and Ce3+ have been realised in order to increase the population of the Er3+ 4I13/2 laser emitting level. Best results are obtained with Ce3+ ion since in the sample containing 6 x 1020 Ce3+/cm3, the Er3+ 4I11/2 level lifetime is divided by a factor of 3 while the Er3+ 4I13/2 fluorescence lifetime remains unaffected. On the contrary, codoping with Nd3+ or Eu3+ ions simultaneously decreases the Er3+ 4I11/2 and 4I13/2 kinetics parameters. The role of the other parameters such as Yb/Er concentrations ratios is also discussed. 相似文献
8.
Transparent glasses in the system (100−x)Li2B4O7–x(SrO---Bi2O3---Nb2O5) (10≤x≤60) (in molar ratio) were fabricated by a conventional melt-quenching technique. Amorphous and glassy characteristics of the as-quenched samples were established via X-ray powder diffraction (XRD) and differential thermal analyses (DTA) respectively. Glass–ceramics embedded with strontium bismuth niobate, SrBi2Nb2O9 (SBN) nanocrystals were produced by heat-treating the as-quenched glasses at temperatures higher than 500 °C. Perovskite SBN phase formation through an intermediate fluorite phase in the glass matrix was confirmed by XRD and transmission electron microscopy (TEM). Infrared and Raman spectroscopic studies corroborate the observation of fluorite phase formation. The dielectric constant (r) and the loss factor (D) for the lithium borate, Li2B4O7 (LBO) glass comprising randomly oriented SBN nanocrystals were determined and compared with those predicted based on the various dielectric mixture rule formalism. The dielectric constant was found to increase with increasing SBN content in LBO glass matrix. 相似文献
9.
Hongyan Wang Guohua Jia Yan Wang Zhenyu You Jianfu Li Zhaojie Zhu Fugui Yang Yanping Wei Chaoyang Tu 《Optical Materials》2007,29(12):1635-1639
Novel pure and cobalt-doped magnesium borate crystals (Mg3B2O6) have been grown successfully by the Czochralski technique for the first time. Crystal growth, X-ray powder diffraction (XRD) analysis, absorption spectrum, fluorescence spectrum as well as fluorescence decay curve of Co2+:Mg3B2O6 (MBO) were described. From the absorption peaks for the octahedral Co2+ ions, the crystal-field parameter Dq and the Racah parameter B were estimated to be 943.3 cm−1 and 821.6 cm−1, respectively. The fluorescence lifetime of the transition 4T1(4P) → 4T2 centered at 717 nm was measured to be 9.68 ms. 相似文献
10.
采用高温固相法制备得到Sr2MgSi2O7: Eu2+和Sr2MgSi2O7: Eu2+, Dy3+发光粉, 并详细研究了Eu2+和Dy3+的掺杂浓度对Sr2MgSi2O7材料的荧光和长余辉性能的影响。所有样品都在470 nm附近呈现较宽的发光峰, 这可归因于Eu2+离子的4f65d→4f7电子能级跃迁。当Eu2+掺杂浓度超过淬灭浓度, 其浓度淬灭效应导致发光粉的荧光强度下降和余辉时间减短。同时, 发射峰的峰位随Eu2+浓度的增加而发生红移, 这主要由于晶体场分裂能和斯托克斯位移变化造成的, 而电子云扩大效应变化所产生的影响相对较弱。Dy3+离子会抑制荧光, 但有助于延长余辉时间。当其掺杂浓度超过10mol%时, Eu2+\Dy3+离子通过隧道复合机制发生浓度淬灭, 从而使材料的长余辉寿命减少。 相似文献
11.
以Y2O3、Eu2O3、Bi(NO3)3·H2O、浓HNO3、偏钒酸铵、氨水、无水乙醇和一缩二乙二醇为原料,采用聚乙烯吡咯烷酮(PVP)辅助水热法合成YVO4: Eu3+, Bi3+纳米颗粒。使用X射线衍射(XRD)、扫描电镜(SEM)、红外光谱(IR)和荧光光谱(FL)等手段对产品进行了表征和分析。结果表明:合成的样品为YVO4: Eu3+, Bi3+纳米颗粒,均具有四方晶相结构,其微结构随反应溶液的的pH值变化。YVO4: Eu3+, Bi3+纳米颗粒在619 nm处有较强的红光发射(电偶极跃迁5D0→7F2),在594 nm有较弱的橙光发射(磁偶极跃迁5D0→7F1)。随着Eu/Bi比值的增大材料的荧光先增强后减弱,在Eu/Bi比值为5时样品的红光发射最强。溶液的pH值影响YVO4: Eu3+, Bi3+纳米晶的发光强度,其中pH值为10时的样品其红光发射最强。并探讨了YVO4: Eu3+, Bi3+纳米晶的发光机理。 相似文献
12.
T. Nakamura M. Katagiri M. Ukibe T. Ikeuchi M. Ohkubo 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2004,520(1-3):67-69
We succeeded in detecting neutrons using superconducting tunnel junctions (STJs) fabricated on a single crystal of Li2B4O7. Neutrons are captured in the crystal by the nuclear reactions 6Li+n→T+alpha+4.78 MeV and 10B+n→7Li+alpha+2.3 MeV, which excite a large number of phonons in the substrate. The phonons propagate in the absorber and are measured by the STJs. We selected a single crystal of Li2B4O7 as the absorber material because of properties such as the large neutron cross-section of 6Li and 10B, low γ-ray sensitivity, short particle range in the substrate, and fast phonon velocity. Series-connected or multiple STJs on the crystal would enable two-dimensional neutron imaging with high detection efficiency, low γ-ray background, and a high spatial resolution of a few microns. In this paper, we demonstrate neutron detection by STJs and report the basic characteristics of the fabricated STJs, including their X-ray response and neutron detection. The correlation in pulse heights between two junctions located 1.3 mm apart clearly indicates the possibility of neutron imaging. 相似文献
13.
The effect of radiation trapping on the emission properties of Er3+-doped tellurite and phosphate glasses has been investigated as the function of sample thickness and doping concentration. It was found that radiation trapping exists generally in two glass matrices, even at low doping concentration (0.1 mol% Er2O3). The larger effect of radiation trapping in tellurite glasses compared with phosphate glasses is due to its larger emission cross-section at 1.5 μm band and the spectral overlap between the emission and absorption spectra of Er3+: 4I13/2 ↔ 4I15/2transition. Due to radiation trapping, the measured lifetime of the Er3+: 4I13/2 level in tellurite glasses increases by about 11–37% with increasing the sample thickness at the different erbium doping concentration, while 6–17% for phosphate glasses. And the full-width at half maximum of fluorescence (FWHM) of Er3+: 4I13/2 → 4I15/2 transition in tellurite glasses increased by about 15–64% with increasing the sample thickness, while 11–55% for phosphate glasses. It caused a high overestimation on the figure of merits (FOM) for amplifier bandwidth (σe × FWHM). 相似文献
14.
Nanocrystalline Gd2O3:A (A=Eu3+, Dy3+, Sm3+, Er3+) phosphor films and their patterning were fabricated by a Pechini sol–gel process combined with a soft lithography. X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and optical microscopy, UV/vis transmission and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the films began to crystallize at 500 °C and that the crystallinity increased with the elevation of annealing temperatures. Uniform and crack free non-patterned phosphor films were obtained by optimizing the composition of the coating sol, which mainly consisted of grains with an average size of 70 nm and a thickness of 550 nm. Using micro-molding in capillaries technique, we obtained homogeneous and defects-free patterned gel and crystalline phosphor films with different stripe widths (5, 10, 20 and 50 μm). Significant shrinkage (50%) was observed in the patterned films during the heat treatment process. The doped rare earth ions (A) showed their characteristic emission in crystalline Gd2O3 phosphor films due to an efficient energy transfer from Gd2O3 host to them. Both the lifetimes and PL intensity of the rare earth ions increased with increasing the annealing temperature from 500 to 900 °C, and the optimum concentrations for Eu3+, Dy3+, Sm3+, Er3+ were determined to be 5, 0.25, 1 and 1.5 mol% of Gd3+ in Gd2O3 films, respectively. 相似文献
15.
Bi2O3·B2O3 glasses doped with rare-earth oxides (RE2O3) (RE3+ = La3+, Pr3+, Sm3+, Gd3+, Er3+ and Yb3+) were prepared by the melting–quenching method. The relationships between composition and properties were demonstrated by IR, DSC, XRD and SEM analysis. The results show that the network structure resembles that of undoped Bi2O3·B2O3 glass, composing of [BO3], [BO4] and [BiO6] units. RE2O3 stabilizes the glass structure as a modifier. Transition temperature (Tg) increases linearly with cationic field strength (CFS) of RE3+. La2O3, Pr2O3, Sm2O3 and Gd2O3 are benefit to promote the formation of BiBO3 crystal. When Er2O3 and Yb2O3 are introduced, respectively, the main crystal phase changes to Bi6B10O24. Transparent surface crystallized samples are obtained by reheating at 460–540 °C for 5 h. In this case, needle like BiBO3 crystal or rare-earth-doped BiBO3 crystal (PrxBi1−xBO3 and GdxBi1−xBO3) are observed, which is promising for non-linear optical application. 相似文献
16.
Kwang-Bok Kim Kyung-Wan Koo Tong-Yul Cho Hui-Gon Chun 《Materials Chemistry and Physics》2003,80(3):682-689
The blue phosphor of BaMgAl10O17:Eu2+ (BAM) powders were prepared by solid-state reaction. The thermal degradation of BAM phosphor significantly reduces the intensity of the blue emission. BAM is reduced by an amount of 50% after heating at around 800 °C for 1 h. Photoluminescence (PL) excitation and emission spectra showed that the blue emission of 450 nm peak decreased with increasing annealing temperature. The 5D0→7F1 and 5D0→7F2 transition of Eu3+ were observed at 590 and 615 nm emission lines over 1100 °C. Electron paramagnetic resonance (EPR) spectrum also detected two signals of Eu2+, corresponding to g=3.7156(9) for 88 mT, and g=2.9507(9) for 133 mT. X-ray absorption near edge structure (XANES) spectrum decreased the intensity of Eu2+ for 6977 eV with increasing annealing temperature, while high-energy peak of Eu3+ for 6984 eV was increased. The combined use of X-ray and neutron data by the Rietveld refinement appears to support that the secondary phase of EuMgAl11O19 magnetoplumbite structure in BAM may be formed by heat treatment. 相似文献
17.
18.
It has been found that charge compensated CaMoO4:Eu3+ phosphors show greatly enhanced red emission under 393 and 467 nm-excitation, compared with CaMoO4:Eu3+ without charge compensation. Two approaches to charge compensation, (a) 2Ca2+ → Eu3+ + M+, where M+ is a monovalent cation like Li+, Na+ and K+ acting as a charge compensator; (b) 3Ca2+ → 2Eu3+ + vacancy, are investigated. The influence of sintering temperature and Eu3+ concentration on the luminescent property of phosphor samples is also discussed. 相似文献
19.
In La2O3-MO-B2O3 ternary system, various glasses/ glass ceramics with M=Ca, Sr and Ba have been prepared. In this ternary system, homogeneous nucleation occuring in the B2O3 melt appears to be the cause for the formation of nanocrystallites, hence glass ceramics. The nucleation process is very much dependent on the alkaline earth used viz., with smaller alkaline earths like Ca, boron prefers (BO4)5− tetrahedral coordination with oxygen, while in the case of bigger alkaline earths like Ba and Sr, (BO3)3− triangular coordination seems to be predominant. Eu3+ in this glass system yields intense 5D0→7Fj emission. A cursory view on the dependence of the various Judd-Ofelt parameters (Ωk) indicates that Ω2 parameter is very much dependent on the immediate vicinity of the luminescent ion (Eu3+) while Ω4 is not. Various results based on these are discussed. 相似文献
20.
Hailian Liang Hiromasa Hanzawa Takashi Horikawa Ken-ichi Machida 《Optical Materials》2007,29(12):1789-1792
High temperature persistent spectral hole burning up to room temperature has been observed in Eu3+ ions doped oxy-fluoride glasses with a composition of 30CaF2–10Al2O3–60B2O3 (mol%) melted in a reducing atmosphere. The hole stability was studied through light-induced hole refilling and temperature cycling experiments. The burned holes survive thermal cycling to 300 K due to a high barrier height of 0.69 eV in the sample. 相似文献