Enhanced mid-IR luminescence of Tm3+ ions in Ga2S3 nanocrystals embedded chalcohalide glass ceramics

Chalcohalide glass with a composition of 65GeS₂–25Ga₂S₃–10CsI (in mol%) doped with 0.6 wt% Tm³⁺ ions was prepared by conventional melt–quench method. By heat treating the precursor glass at 20 °C above its glass transition temperature T_g for different durations, IR transparent glass ceramics were obtained. X-ray diffraction (XRD) and scanning electron microscope (SEM) showed that Ga₂S₃ crystallites were precipitated after heat treatment and their grain sizes were in nano-scale and increased with the elongation of heat treated time. Mid-IR luminescence properties of the glass and transparent glass ceramic samples were investigated. The emissions at 2.3 and 3.8 μm corresponding to optical transitions of ³H₄ → ³H₅ and ³H₅ → ³F₄ of Tm³⁺ ions were significantly enhanced by the presence of Ga₂S₃ nanocrystals and reached a maximum after 8 hours treatment.     

Tb3+-impregnated,non-porous silica glass possessing intense green luminescence under UV and VUV excitation

A colorless transparent luminescence material was successfully prepared by impregnation of leached, porous glass with Tb³⁺ ions followed by reductive sintering in a CO atmosphere. Tb³⁺ emissions under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation clearly showed the most intense emission band to be situated at 543 nm, which corresponds to the ⁵D₄ → ⁷F₅ transition. Sintering of the Tb glass in a reducing atmosphere resulted in a significant enhancement of Tb³⁺ emission intensity in comparison with sintering in air. The presence of traces of cerium ions was verified in Tb glasses, and more Ce³⁺ ions were produced as a result of the reductive sintering. The increase in Ce³⁺ ions was believed to be mainly responsible for the enhancement of ⁵D₃ → ⁷F_j and ⁵D₄ → ⁷F_j transitions from Tb³⁺ ions owing to an energy transfer channel. A clearly defined difference in the spectral energy distribution of Tb³⁺ emissions was found for 231 nm UV and 160 nm VUV excitation of the Tb glass. The phenomenon of cross relaxation was only observed under 231 nm UV excitation. Different excitation mechanisms were taken into account. Direct excitation of Tb³⁺ ions together with Ce³⁺ ions occurred in the Tb glass under the 231 nm UV light, whereas indirect excitation consisting of host absorption of energy and transfer from host to Tb³⁺ ions occurred under the 160 nm VUV light.     

Energy transfer from Bi3+ sensitizing the luminescence of Eu3+ in clusters embedded into sol–gel silica glasses

Y³⁺(La³⁺), Eu³⁺ and Bi³⁺ ions co-doped sol–gel silica glasses were synthesized. Photoluminescence spectra show that there is energy transfer from Bi³⁺ ions to the emission band of Eu³⁺ ions. The co-dopants Y³⁺ or La³⁺ have strong effects on the local structure and luminescence of Eu³⁺ ions. For 0.5 mol% Eu³⁺ ions doped glasses, the co-doping of 1 mol% Bi³⁺ and 1 mol% Y³⁺ is the most appropriate for the sensitization from Bi³⁺ to Eu³⁺. The sensitization effectiveness from Bi³⁺ ions to Eu³⁺ ions was studied by changing the amount of Bi³⁺ and Y³⁺, and clusters containing rare earth ions and Bi³⁺ ions dominate the energy transfer processes. The comparison of luminescent R-values (the intensity ratio of ⁵D₀ → ⁷F₂/⁵D₀ → ⁷F₁ in Eu³⁺ ions) between glasses containing La³⁺ and containing Y³⁺ verifies the formation of clusters in sol–gel glasses. As a favorable configuration for energy transfer, the accurate design and synthesis of clusters-contained glasses may provide a new kind of luminescent materials.     

Novel luminescence behaviors of Ce3+/Tb3+ co-doped phosphate glasses

In the present work, Ce³⁺/Tb³⁺ co-doped 60P₂O₅-30BaO-10B₂O₃ phosphate glasses are prepared and their luminescence properties are presented. Under excitation at 303 nm, the Ce³⁺ ions singly doped sample show a novel red emission besides the UV one. The co-doped samples show enhanced Tb³⁺ ions emission with the increasing of Tb³⁺ ions concentration at the cost of Ce³⁺ emission. The mechanism of this luminescent behavior is discussed with respect to the relevant energy transfer process.     

Improvement of luminescent materials composed of Tb(III) ions,WO3 nanoparticles and silica xerogel as a matrix

Nanoparticles of tungsten trioxide, WO₃, are used to enhance the luminescence emission intensity of terbium(III) ions embedded in a silica matrix. Optically active components have been incorporated into silica xerogel by impregnation of silica xerogel immersed firstly in WO₃ sol and subsequently in a solution with Tb(III). Photoluminescence studies make it possible to describe a plausible mechanism of the Tb(III) enhanced luminescence that could be attributed to energy transfer via excited WO₃ nanoparticles to Tb(III) ions in the system: Tb(III) ions–WO₃ nanocrystals–SiO₂. The effect related to WO₃ nanoparticles of various sizes influences not only changes in the emission intensity and band shifting of WO₃ nanostructures but also the same spectral parameters of the emitting Tb(III) ions.     

Enhanced luminescent properties of Tb3+ ions in transparent glass ceramics containing BaGdF5 nanocrystals

Tb³⁺ doped transparent oxyfluoride glass ceramics containing BaGdF₅ nanocrystals were prepared. The transmission spectra, photoluminescence spectra, decay time and X-ray excited luminescence spectra of the Tb³⁺-doped glass and glass ceramics were investigated. Energy transfer from Gd³⁺ to Tb³⁺ has been observed in the glass and glass ceramics. The emission intensity of green band (⁵D₄ → ⁷F_J) of the Tb³⁺-doped glass ceramics is enhanced compared with that of the glass under ultraviolet and X-rays, which could be attributed to that the generation of BaGdF₅ nanocrystals with low phonon energy reduces the non-radiative transitions.     

Upconversion luminescence in Ho3+/Yb3+- and Tb3+/Yb3+-codoped fluorogermanate glass and glass ceramic

Energy-transfer excited upconversion luminescence in Ho³⁺/Yb³⁺- and Tb³⁺/Yb³⁺-codoped PbGeO₃–PbF₂–CdF₂ glass and glass–ceramic under infrared excitation is investigated. In Ho³⁺/Yb³⁺-codoped samples, green (545 nm), red (652 nm), and near-infrared (754 nm) upconversion emission corresponding to the ⁵S₂(⁵F₄) → ⁵I₈, ⁵F₅ → ⁵I₈, and ⁵S₂(⁵F₄) → ⁵I₇ transitions, respectively, was observed. Blue (490 nm) emission assigned to the ⁵F_2,3 → ⁵I₈ transition was also detected. In the Tb³⁺/Yb³⁺-codoped system, bright UV–visible emission around 384, 415, 438, 473–490, 545, 587, and 623 nm, identified as due to the ⁵D₃(⁵G₆) → ⁷F_J(J = 6, 5, 4) and ⁵D₄ → ⁷F_J(J = 6, 5, 4, 3) transitions, was measured. The comparison of the upconversion process in glass ceramic and its glassy precursor revealed that the former samples present much higher upconversion efficiencies. The dependence of the upconversion emission upon pump power, and doping contents was also examined. The results indicated that successive energy-transfer between ytterbium and holmium ions and cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The viability of using the samples for three-dimensional solid-state color displays is also discussed.     

Characterization of low-density silica xerogel formed into microspheres

Low-density silica xerogels were formed into spherical pellets using a process in which a xerogel suspension containing sodium alginate was solidified through free fall in a solution of divalent ions that induce the droplet solidification. Pellet preparation was also carried out at laboratory scale by using a syringe instead of the material-consuming unit used for scaling up. When beads are made from a suspension of dried-and-calcined xerogel material, the textural properties such as porosity and surface area are significantly altered. Both properties are reduced by 30-50% compared to the starting reference material. Properties were improved when a suspension of dried xerogel that is less sensitive to contact with water was used: specific surface area was maintained at its initial level and porosity decreased by 25%.     

Colour centre in YAG: Cr3+ crystals

YAG crystals doped with 0.01 wt% Cr were grown by Czochralski method using 98% Ar + 2% H₂ protective atmosphere. Four colour varieties of the crystals were prepared in the dependence of the Al₂O₃ :Y₂O₃ ratio in the melt and the sign of electrical potential above the melt level. New absorption bands were attributed to the O⁻ centre (400 to 480 nm), F centre (357, 500, and 833 nm) or Cr³⁺ at another site than octahedral (455, and 612 nm).     

Energy transfer and surface plasmon resonance in luminescent materials based on Tb(III) and Ag or Au nanoparticles in silica xerogel

Two-component material consisting of terbium(III) ions doping silica xerogel prepared by sol–gel procedure shows enhanced Tb(III) photoluminescence. We postulate that in this material the enhancement is owing to energy transfer from one of the defect states in silica to emitting states ³D₃ and ⁵D₄ of Tb(III).Surface plasmon resonance effect causes two contrary phenomena. Thus, if in the vicinity of the Tb(III) emission centers are present nanoparticles of Ag, observed is additional improvement of the Tb(III) emission. While, presence of Au nanostructures in the silica doped with Tb(III) causes quenching of the luminescence. In general, both the three-component materials exhibit enhancement of the component silica emission band in the resultant 380 nm band and relatively high thermal stability, especially above 600 °C.     

Tb3+,Yb3+共掺杂LuBO3荧光粉的下转换发光

利用水热法成功合成了近红外量子剪裁荧光粉LuBO3∶15;Tb3+,x; Yb3+(x=0,1,2,4,8,12).通过X射线衍射(XRD)、光致发光谱(PL)、激发谱(PLE)和荧光寿命测试了合成物质的物相结构与发光性质.在286 nm(Tb3+∶7 F6→5D)紫外光激发下,观察到了Tb3∶5D4→7Fj(J=6,5,4,3)可见波段特征发射光和Yb3+:2F5/2→2F7/2的近红外光.研究了Yb3+浓度与激发发射光谱和荧光寿命之间的关系,表明Tb3+和Yb3+之间存在能量传递.当Tb3和Yb3+掺杂摩尔浓度分别为15;和2;时,近红外发射最强.计算得知,其最大下转换量子效率为160.74;.     

Sol–gel synthesis and optical properties of size controlled Indium Arsenide nanocrystals embedded in silica glasses

III–V semiconductor Indium Arsenide (InAs) nanocrystals embedded in silica glasses was synthesized by combining the sol–gel process and heat treatment in H₂ gas. The size of InAs nanocrystals can be easily controlled via changing the In and As content in the starting materials and the heating temperature in a H₂ gas atmosphere. Absorption measurements indicate a blue shift in energy with a reduction on the In and As content in the SiO₂ gel glasses as a result of quantum confinement effects. A near-infrared photoluminescence with peak at 3.40 μm was observed at 6 K under 514.5 nm Ar⁺ laser excitation from InAs nanocrystals embedded in the silica gel glasses.     

Ce3+:YAG晶体位错的研究

本文报导了用中频感应加热提拉法生长Ce3+:YAG晶体,直径达45mm.对样品采用不同的化学试剂进行了时间不等的腐蚀,用偏光显微镜观察到不同形貌的位错蚀坑,分析了位错与晶体结构及生长工艺参数等因素之间的关系.     

LiCaPO_4∶Tb~(3+)材料的制备及其发光特性

采用高温固相法合成了LiCaPO4∶Tb3+绿色荧光粉,并研究了材料的发光性质。LiCaPO4∶Tb3+材料呈多峰发射,发射峰位于437 nm、491 nm、545 nm、587 nm和625 nm,分别对应Tb3+的5D3→7F4和5D4→7FJ=6,5,4,3跃迁发射,主峰为545 nm;监测545 nm发射峰,所得激发光谱由4f75d1宽带吸收(200~330 nm)和4f-4f电子吸收(330~400nm)组成,主峰为380 nm。研究了Tb3+掺杂浓度,电荷补偿剂Li+、Na+、K+和Cl-及敏化剂Ce3+对LiCaPO4∶Tb3+材料发射强度的影响,发现调节激活剂浓度、添加电荷补偿剂或敏化剂均可提高材料的发射强度。     

Yb3+在YAG中的哈密顿参数计算

由吸收和发射光谱确定了提拉法生长的(29.52at;) Yb∶ YAG晶体的Yb3+能级,由叠加模型拟合了它的旋轨耦合参数、内禀晶体场参数Bk(k=2,4,6),然后以Bk得到的晶体场参数作为初始参数拟合了Yb3+的晶场能级,从而获得了它的晶体场参数Bqk,拟合误差为2 cm-1.所得的哈密顿参数可用于计算Yb∶ YAG的波函数,以进一步分析它的发光或激光微观机理.     

Recombination luminescence of oxygen-deficient centers in silica

The luminescence of silica glass, prepared by plasma chemical vapor deposition (PCVD) and quartz glass of type IV (trade mark KS-4V) methods, were studied while irradiated with pulses of ArF laser (193 nm) light in the range of sample temperatures between 10 and 300 K. The samples contain less than 0.1 ppm metallic and hydroxyl impurities. The samples synthesized by PCVD were of two kinds. The first one (amorphous) was as-deposited from plasma at a substrate tube temperature of ～1200 °C. The second one (fused) was prepared from the first by the tube collapsing with an external burner. In this process, a section of the substrate tube with the deposited glass was installed in a lathe and processed at a temperature of ～2100 °C during ～20 min until the tube was transformed to a rod. After such processing, the rod was cooled down to room temperature in air at an average rate of about 400 °C per min. The only observed luminescence possesses two broad bands, with not well defined position, one at 2.6–2.9 eV (a blue band) and another in the range of 4.4 eV (an UV band). There is a correspondence in luminescence properties between KS-4V silica and fused PCVD silica. Those bands have been attributed to oxygen deficient centers (ODC). No luminescence is observed in amorphous PCVD silica under irradiation with 193 nm laser light. So, formation of the sample by melting at least stimulates formation of ODCs at 193 nm. The blue band decays obeys to power law ～t^?1 and is detected in the range of time 10 ns to 300 μs. The UV band possesses a fast, practically repeating excitation pulse, and a slow component (～30 μs). The obtained new kinetics data are compared with known in literature for lone twofold-coordinated silicon having exponential decay for the blue band equal to 10 ms and 4.5 ns for the UV band. That shows the blue band of new studied samples under ArF laser possesses decay component faster and the UV band slower than that of the twofold-coordinated silicon center. This corresponds to the recombination process of luminescence excitation by laser. We propose a model of the processes as charge separation under excitation with creation of a nearest self-trapped hole and electron trapped on the twofold-coordinated silicon, modified by its surrounding atoms or ions. This pair is recombining then with luminescence.     

ZrO2:Tb3+纳米晶的制备与发光研究

本文用共沉淀法制备了纳米晶ZrO2:Tb3+荧光粉,并对它的晶体结构、颗粒大小和光致发光性质进行了表征.XRD测试结果表明:以此工艺制备的纳米晶ZrO2:Tb3+含有单斜相和四方相两种微观结构,四方相所占比例随着Tb3+离子浓度的提高而提高,Tb3+离子的掺入有稳定ZrO2四方晶相的作用.纳米晶ZrO2:Tb3+粉体中Tb3+的强室温特征发射的两个主发射带为5D3→7F1和5D4→7F1的跃迁.荧光强度与Tb3+浓度的关系研究表明:5D3和5D4能级有不同的猝灭规律,由于(5D3,7F6)→(5D4,7Fo)的交叉弛豫,使得5D3→7F5跃迁的猝灭浓度较低,在我们的实验中,掺1.5;摩尔分数Tb3+时5D3→7F1跃迁发射最强,掺6;摩尔分数Tb3+时5D4→7F1跃迁发射最强.     

Structural and optical spectroscopy of LiNbO3:Tm nanocrystals embedded in a SiO2 glass matrix

Transparent SiO₂:Li₂O:Nb₂O₅ glass doped with Tm³⁺ has been prepared by the sol–gel method, and heat-treated in air (HT) at temperatures between 500 and 800 °C. X-ray diffraction (XRD) patterns and Raman spectroscopy show SiO₂ and LiNbO₃ phases in samples HT above 650 °C, and a NbTmO₄ phase for T > 750 °C. The XRD SEM analysis show increasing particle size and number with the increase of HT temperature. Intra-4f¹² transitions due to Tm³⁺ ion dispersed in the matrix are observed in samples with T > 650 °C. The luminescence is dominated by the ¹G₄ → ³F₄ (～650 nm), ¹D₂ → ³F₃ (～780 nm), ³H₄ → ³H₆ (～800 nm), ³H₅ → ³H₆ (～1200 nm) and ³H₄ → ³F₄ (～1500 nm) transitions under resonant excitation to the ion levels.     

GdAlO3∶Tb3+-Al2O3有序共晶生长及其微结构研究

两相有序共晶材料由于具有不同折射率的两晶相呈现有序排列,可降低荧光在共晶材料内部的散射而实现导光功能,可被应用于高分辨探测成像器件中。本工作根据定向凝固原理,用微下降法生长技术制备得到了直径为3 mm的GdAlO₃∶Tb³⁺-Al₂O₃两相有序共晶。通过SEM和元素分析,探究了GdAlO₃∶Tb³⁺-Al₂O₃共晶内部的微结构,结果显示,所得共晶中GdAlO₃∶Tb³⁺晶相均匀有序地分布于基质Al₂O₃晶相中,GdAlO₃∶Tb³⁺晶相直径的大小受生长速率的影响,速率越快,直径越小。所制备得到的GdAlO₃∶Tb³⁺-Al₂O₃有序共晶在X射线辐照下发射出明亮的绿色荧光,并在GdAlO₃∶Tb³⁺晶相中定向传播,有望被用作X射线探测成像材料,提高探测器的空间分辨率。     

Hydrothermal synthesis and luminescent properties of YBO3:Tb3+ uniform ultrafine phosphor

The pure hexagonal phase YBO₃:Tb³⁺ phosphors with good crystallinity and uniform size were prepared by hydrothermal reaction (HR). The particle size and morphology can be well controlled by adjusting the concentration of ammonium acetate and varying the reaction temperature and time. The phosphor prepared by HR emits an intense green light at 543 nm, which is stronger than that from crystals synthesized by solid-state reaction (SR). The influence of Tb³⁺-doping concentration on the crystallization and luminescent properties were investigated. The results showed that the samples exhibited a higher quenching concentration of Tb³⁺ in comparison with those prepared by the SR. The phenomena were also discussed.