Ultra-violet emission in Ho:ZBLAN fiber

We report on the short wavelength (green, blue, and ultra-violet (UV)) emission in trivalent holmium doped fluoro-zirconate fiber (Ho³⁺:ZBLAN) under direct and upconversion pumping. Efficient red to UV upconversion has been observed using 647 nm cw pumping by krypton ion laser. A close to cubic UV signal intensity dependence on incident red pump power was determined, confirming the three-photon character of the observed process. The responsible upconversion mechanisms were investigated and shown to be excited state absorption (ESA) via low-lying ⁵I₇ and ⁵I₆ sates. Dynamics of the involved excited states have been studied under pulsed laser excitation.     

Spectroscopic properties of LaAlO3 doped with Ho

Absorption and emission as well as emission decay times of Ho³⁺ ions embedded in LaAlO₃ single crystal were measured. The experimental results were analysed in the frame of the Judd–Ofelt theory. Energy levels, oscillator strengths and probabilities of radiative transitions were determined. The results indicate on nonradiative transitions due to cross-relaxation down and up-conversions processes.     

Spectral properties of Ho:GdVO4 single crystal

Absorption and emission spectral properties of GdVO₄ single crystal doped with Ho³⁺ ions were investigated at room temperature. Polarized absorption cross section is calculated in the range of 400–2200 nm. Results were analyzed and parameters were calculated based on Judd-Ofelt theory, the emission spectrum shows that the emission intensity around the wavelength of 546 nm associated with transition ⁵S₂ → ⁵I₈ is much stronger than other bands in the observed range and potentially enable the green light output around this emission band in this crystal.     

Optical absorption and spectroscopic characteristics of Tm ions doped NaY(MoO4)2 crystal

The polarized absorption and emission spectra have been measured for the Tm³⁺ doped NaY(MoO₄)₂ crystal and spectral parameters have been estimated from the absorption data based on the Judd–Ofelt theory. The effective intensity parameters (t = 2, 4, 6) are 11.67 ×10⁻²⁰, 2.21 × 10⁻²⁰, 1.74 × 10⁻²⁰ cm², respectively. From the intensity parameters, the radiative transition probabilities, radiative lifetimes, branching ratios and the emission cross-section have been calculated. In comparison with other Tm³⁺ doped laser crystals, Tm³⁺:NaY(MoO₄)₂ crystal has potential as a promising laser crystal.     

MgAl2O4:Eu3+荧光粉的制备及其光谱特性

采用水热辅助固相法合成一系列Eu³⁺掺杂MgAl₂O₄:Eu³⁺荧光粉。主要考察粉体的物相结构、形貌、颗粒尺寸及电/磁偶极跃迁强度随Eu³⁺摩尔分数的变化规律。结果表明:当Eu³⁺不等价取代Mg²⁺后并未影响基质材料的晶体结构,产物全部为立方相MgAl₂O₄,但间隙O^2?的存在会影响被取代离子Mg²⁺的配位关。当Eu³⁺掺入时,其会与溶液中的NH₄⁺共同参与调控样品的形貌和尺寸,以致片状颗粒的厚度减小、不规则程度加剧。基于J-O理论认为,在248 nm紫外和395 nm近紫外光激发下,Eu³⁺在MgAl₂O₄中所处格位的对称性差异是引起电偶极(⁵D₀→⁷F₂)和磁偶极(⁵D₀→⁷F₁)跃迁相对强度不同的主要原因。     

以Mn3O4为前驱体制备尖晶石型LiMn2O4及其性能

采用改进的固相反应法合成了高性能的锂离子电池正极材料LiMn2O4。首先,以廉价的MnSO4为原料,通过水解氧化法制备纳米级Mn3O4前驱体;然后,将Mn3O4和Li2CO3混合均匀,在750℃固相反应20 h,得到尖晶石型LiMn2O4。用X射线衍射(XRD)和扫描电镜(SEM)对Mn3O4前驱体和LiMn2O4样品进行表征,用充放电测试和循环伏安技术对LiMn2O4样品进行电化学性能研究。结果表明:所制备的LiMn2O4具有完整的尖晶石型结构,且晶体粒子分布均匀。所制备的LiMn2O4材料在3.0~4.4 V之间,室温(25℃)下,在0.2C倍率下首次放电比容量为130.6 mA.h/g;在0.5C倍率下首次放电比容量为127.1 mA.h/g,30次循环后,容量仍有109.5 mA.h/g,且样品具有较好的高温性能。     

Luminescence properties of Ca10K(PO4)7:RE (RE = Ce, Tb, Dy, Tm and Sm) under vacuum ultraviolet excitation

A series of RE³⁺ (RE = Ce, Tb, Dy, Tm and Sm) activated Ca₁₀K(PO₄)₇ were synthesized by conventional state reaction and their photoluminescence properties under vacuum ultraviolet excitation were investigated. The PO₄³⁻ absorption lies within the range from 125 to 180 nm in all the excitation spectra of Ca₁₀K(PO₄)₇:RE³⁺. The first f-d transition of Ce³⁺ is observed at 316 nm, and the Ce³⁺ emission is located at about 350 nm. Both the first spin-allowed and spin-forbidden f-d transitions of Tb³⁺ are situated at 232 and 263 nm, respectively. The emission spectrum of Ca₁₀K(PO₄)₇:Tb³⁺ exhibits typical Tb³⁺ emissions with the predominant peak at 544 nm. The O²⁻-Dy³⁺ charge transition band was calculated and identified around 173 nm, the CIE chromaticity coordinates of Dy³⁺ were calculated to be 0.364 and 0.392. The Ca₁₀K(PO₄)₇:Tm³⁺ demonstrates the strongest excitation at about 182 nm assigned to O²⁻-Tm³⁺, and gives the predominant emission at 453 nm. The ⁴G_5/2-⁶H_7/2 transition of Sm³⁺ at 601 nm is the most intensive in the emission spectrum.     

Correlation between the surface state and optical properties of S6 site and C2 site in nanocrystalline Eu:Y2O3

Eu³⁺ doped Y₂O₃ nanocrystals are synthesized via precipitation and hydrothermal methods. With the increase of hydrothermal temperature, the number of surface states decreases when nanorods are formed. The decrease of surface states induces the increase in the ratio of S₆ site to C₂ site, and meanwhile results in the spectral red-shift of charge transfer band as well as the enhancement of red emission. The results indicate that the surface states and optical properties have close correlations.     

Effects of Bi doping on the optical properties of Er:Y2O3

The influences of Bi³⁺ doping on the optical properties of Er³⁺:Y₂O₃ are investigated under UV and IR excitations. The emission intensity of Er³⁺ is remarkably enhanced by the introduction of Bi³⁺ under both two excitations. The emission enhancement under UV excitation originates from the energy transfer from Bi³⁺ to Er³⁺, while under IR excitation it can be attributed to the modification of the local crystal field around the Er³⁺.     

Infrared spectroscopic properties of Tm, Ho:NaY(WO4)2 single crystals

Singly doped and Tm³⁺/Ho³⁺ co-doped NaY(WO₄)₂ single crystals were grown successfully by Czochralski method. The room temperature polarized absorption and fluorescence spectra as well as the decay curves were measured. Spectroscopic parameters related to the laser operation around 2.0 μm via the ³F₄ → ³H₆ (Tm³⁺) and ⁵I₇ → ⁵I₈ (Ho³⁺) transitions have been evaluated. The energy level scheme and energy transfer processes of Tm³⁺ and Ho³⁺ were analyzed.     

Co掺杂ZnAl2O4纳米颗粒的制备与光学性质研究

以CTAB为表面活性剂,采用水热法成功制备了不同掺杂比例的Zn1-xCoxAl2O4（x=0,0.20,0.40和0.60）纳米晶。并对样品的晶体结构、形貌、化学成分、价态和光学性能进行表征。实验结果表明,本方法所制备的不同掺杂浓度的Zn1-xCoxAl2O4纳米颗粒为尖晶石结构,晶化程度良好。根据XRD数据计算了晶胞参数a、晶格间距dhkl、晶粒尺寸D,随着掺杂Co离子浓度的增加,均表现为减小趋势。XPS能谱显示大多数Co离子占据四面体中心位置,但有少量的Co离子占据八面体中心位置。随着掺杂Co离子浓度的增加,紫外吸收光的强度逐渐增加。     

孔道Al2O3/SiO2对NaAlH4-Tm2O3体系储氢性能的影响

以机械球磨法制备具有可逆吸放氢性能的NaAlH4-Tm2O3储氢材料体系。利用相同制备方法进一步研究两种不同孔道材料(大孔Al2O3与介孔SiO2)对NaAlH4-Tm2O3体系储氢性能的影响,测试样品的循环吸放氢性能,并对样品吸放氢前后的结构进行表征。结果表明:大孔Al2O3材料的添加并不能明显改善NaAlH4-Tm2O3体系的放氢速率和放氢量,而介孔SiO2的加入使NaAlH4-Tm2O3体系在150℃条件下5 h内的首次放氢量(质量分数)达到4.61%,高于NaAlH4-Tm2O3体系的4.27%,增加了约8.0%。此外,添加介孔SiO2的NaAlH4-Tm2O3体系放氢速率也有所提高。     

Effect of Zn and Li codoping ions on nanosized Gd2O3:Eu phosphor

Nanosized Gd_1.92−x−yZn_xLi_yEu_0.08O_3−δ phosphor was fabricated by combustion synthesis. The effect of Zn²⁺ and Li⁺ ions on the crystallization behavior, morphology, and luminescence property of Gd₂O₃:Eu³⁺ was investigated. The results indicated that incorporation of Zn²⁺ and Li⁺ ions into Gd₂O₃:Eu³⁺ nanoparticles (NPs) could lead to a remarkable increase of photoluminescence or X-ray excited luminescence, and the intensity at 612 nm was increased by a factor of 7.1 or 21.5 in comparison with that of undoped sample. The enhanced luminescence was regarded as the results of the creation of oxygen vacancies due to the Gd³⁺ sites occupied by Li⁺ ions, the alteration of the crystal field surrounding the activator Eu³⁺ ions owing to the incorporation Zn²⁺ ions into interstitial sites, and the flux effect of Zn²⁺ and Li⁺ ions. The Zn- and Li-codoped Gd₂O₃:Eu³⁺ phosphor with highly enhanced luminescence is very encouraging for applications in high-resolution display devices.     

Synthesis, characterization and microwave dielectric properties of nanocrystalline CaZrO3 ceramics

The energy-transfer mechanisms and frequency upconversion emissions in 0.5Er³⁺/xHo³⁺ co-doped tellurite glasses by exciting at 980 nm have been investigated. Three intense upconversion luminescence emissions are observed at around 525, 548, and 660 nm, which correspond to Er³⁺:²H_11/2 → ⁴I_15/2, Er³⁺:⁴S_3/2 → ⁴I_15/2 + Ho³⁺:⁵S₂(⁵F₄) → ⁵I₈, and Er³⁺:⁴F_9/2 → ⁴I_15/2 + Ho³⁺:⁵F₅ → ⁵I₈ transitions, respectively. The upconversion emissions reach the maximum values when Ho₂O₃ is 0.5 mol%, and the intensities of the green and red light emissions were about 4.5 and 6 times stronger than those un-doped Ho₂O₃, respectively. The possible upconversion mechanisms and energy transfer between Er³⁺ and Ho³⁺ were also estimated and evaluated. All the three emissions are based on two photon absorption processes.     

Solvothermal synthesis and characterization of size-controlled Fe3O4 nanoparticles

Size-controlled Fe₃O₄ nanoparticles were prepared via a facile solvothermal method by using the mixed surfactants of SDS and PEG as protective reagents. The sizes of the nanoparticles can be varied from 15 to 190 nm by adjusting the experimental conditions. The influences of the protective reagents, reaction time, the initial concentration of the reactant, molar ratio of FeCl₃ and protective reagents on the size of the produced nanoparticles were studied. The size and morphology of the products were investigated in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and scanning electron microscopy (SEM).     

Upconversion luminescence in Er/Yb codoped Y2CaGe4O12

Calcium yttrium tetrametagermanates Y₂CaGe₄O₁₂ doped with Er³⁺ and Er³⁺/Yb³⁺ reveal upconversion emission in visible spectral range under near-infrared excitation, λ_ex = 980 nm. For the solid solution Er_xY_2−xCaGe₄O₁₂ concentration dependencies for the green and red lines of the visible emission around 526 nm (²H_11/2 → ⁴I_15/2), 545 nm (⁴S_3/2 → ⁴I_15/2) and 670 nm (⁴F_9/2 → ⁴I_15/2) show the optimal value for the sample x = 0.2. The power dependence of the visible luminescence measured at room temperature in the low-power limit indicates two-photon upconversion process. Direct intensification of the upconversion emission signals has been achieved by ytterbium sensitizing. The other upconversion excitation mechanism in Y₂CaGe₄O₁₂:Er³⁺ is discussed for an 808 nm incident laser irradiation. A scheme of excitation and emission routes involving ground/excited state absorption, energy transfer upconversion, nonradiative multiphonon relaxation processes in trivalent lanthanide ions in Y₂CaGe₄O₁₂:Er³⁺ and Y₂CaGe₄O₁₂:Er³⁺, Yb³⁺ has been proposed. Conditions for visible emission occurrence under quasi-resonance λ_ex = 1064 nm excitation depending on pump power values are considered. In the low-power regime only near-infrared emission caused by the transition ⁴I_13/2 → ⁴I_15/2 in erbium ions has been detected.     

Hydrothermal synthesis and photoluminescence of Ce and Tb doped La2Sn2O7 nanocrystals

Phase-pure Ce-/Tb-doped and co-doped lanthanum stannates (La₂Sn₂O₇) nanocrystals were synthesized by a co-precipitation process combined with hydrothermal techniques without any further heat treatment. The crystal structure, particle size, morphologies, and photoluminescence properties of the as-synthesized products were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The as-prepared samples were single-phase cubic pyrochlore-type nanocrystals with a typical size of 10-20 nm. PL spectra showed a dominating green-emitting line around 544 nm attributing to ⁵D₄-⁷F₅ magnetic dipole transition for Tb³⁺ doped and Ce³⁺/Tb³⁺ co-doped La₂Sn₂O₇ nanocrystals. Meanwhile, the concentration quenching phenomenon was observed in both La_2−xTb_xSn₂O₇ and La_1.82−xCe_xTb_0.18Sn₂O₇ nanocrystals. Furthermore, an interesting enhancement of the energy transfer induced green emission was observed in the as-synthesized La_1.82−xCe_xTb_0.18Sn₂O₇ nanocrystals.     

Characterization of crystal field and nuclear quadrupole interactions in the D1 state of Am in LaCl3 and CaWO4

The crystal field splitting and hyperfine energy level structure in the first ⁵D₁ excited state of ²⁴³Am³⁺ in LaCl₃ and CaWO₄ have been studied using selective laser excitation, Zeeman and spectral hole burning experiments. Two crystal field levels and associated vibronic structures were observed in the electric dipole forbidden ⁷F₀↔⁵D₁ transition, that has a very weak magnetic dipole moment. The hyperfine energy level structure, including nuclear quadrupole splitting, was resolved in spectral hole burning studies. The existing free ion and crystal field interaction model provides a consistent interpretation of the observed ordering of crystal field levels and the magnitude of the nuclear quadrupole splitting of ²⁴³Am³⁺ in CaWO₄, whereas a discrepancy between the model and experimental results is encountered for ²⁴³Am³⁺ in LaCl₃. A discussion on the relationship between nuclear quadrupole interaction and free ion modeling is given.     

Preparation and luminescent properties of Eu doped Sr3La(PO4)3 phosphor

Eu²⁺-doped Sr₃La(PO₄)₃ phosphors were synthesized by solid-state reaction method. Their luminescent properties were investigated. The phosphor could be excited by ultraviolet light effectively. The emission spectra exhibit two emission peaks located at 418 nm and 500 nm, respectively. These two peaks originated from two different luminescent centers, respectively. One is nine-coordinated Eu(I) center, other is six-coordinated Eu(II) center. It was found that the doping concentration of Eu²⁺ ions affected the shape of emission spectra. As the doping concentration increasing, Eu²⁺ ions are more likely to form Eu(I) luminescent centers and emit purple light.     

Lu_2O_3:Yb~(3+),Tm~(3+)纳米晶的制备和上转换发光性能(英文)

采用碳酸氢铵(NH4HCO3)为沉淀剂,用共沉淀法制备Yb3+和Tm3+共掺杂的Lu2O3:Yb3+,Tm3+纳米晶。研究Tm3+摩尔分数、Yb3+摩尔分数和煅烧温度对Lu2O3:Yb3+,Tm3+纳米晶的结构和上转换发光性能的影响。结果表明:所制备的纳米晶具有纯的Lu2O3相,结晶性较好。当掺杂的Tm3+浓度超过0.2%(摩尔分数)时,出现浓度淬灭效应。Tm3+和Yb3+的最佳掺杂比分别为0.2%和2%(摩尔分数)。在980nm半导体激光器的激发下,样品发射出蓝光(490nm)和红光(653nm),分别对应Tm3+的1G4→3H6和1G4→3F4跃迁。发射强度与激发功率的关系表明,Tm3+的1G4能级布居是三光子能量传递过程。随着煅烧温度的升高,上转换发光强度增强,这主要是因为随着温度的升高纳米晶表面的OH?减少和纳米晶尺寸增大。