Microstructural and optical characterization of TiO2 doped with ytterbium synthesized by sol-gel and Solar physical vapor deposition process

Pure and ytterbium doped TiO2 nanopowders in anatase phase have been prepared by sol-gel method (SGM) and Solar Physical Vapour Deposition process (SPVD). The physico-chemical parameters of the nanopowders have been described based on the results of micro-structural characterization performed by X-ray diffractometry, scanning electron microscopy, atomic force microscopy, and nitrogen sorption measurements. Thus, final micro-structural properties of SGM and SPVD titania nanopowders have been compared in detail revealing significant changes in the structure and morphology of these two types of materials. Addition of ytterbium had no significant effect on above-mentioned properties, although it modifies significantly the optical properties of the investigated materials. The luminescent properties of developed material were found to be comparable to bulk oxide materials and better than these reported earlier for ytterbium doped titania. In particular it has been shown that the luminescence of SPVD nanopowders is significantly stronger than this of SGM samples.     

Two-phase solvothermal synthesis of rare-earth doped NaYF4 upconversion fluorescent nanocrystals

The synthesis, characterization, and fluorescent spectra of rare-earth doped NaYF₄ upconversion nanocrystals are introduced in this paper. The nanocrystals were synthesized in the water-ethanol-oleic acid system via a two-phase solvothermal approach, by using rare-earth stearate as the precursor. The as-prepared nanocrystals were of hexagonal phase, strong UC fluorescent intensity, with an average size of about 25 nm, which have been characterized by TEM, SAED, powder XRD, and luminescence spectroscopy. The possible mechanism of this synthesis that the nucleation and growth of nanocrystals occurred at the solid-liquid interface was also discussed. The nanocrystals are hydrophilic, and expected to fulfil the demand for biological applications via further modification.     

Er3+/Yb3+ codoped oxyfluoride borosilicate glass ceramic containing NaYF4 nanocrystals for amorphous silicon solar cells

Transparent oxyfluoride borosilicate glass ceramic containing cubic NaYF₄ nanocrystals were successfully fabricated. The cubic NaYF₄ nanocrystals with average size of 30 nm were precipitated in the glass matrix, which was confirmed by the X-ray diffraction and TEM results. In comparison with the as-made glass, significant enhancement of upconversion luminescence is observed in the Er³⁺/Yb³⁺ codoped transparent glass ceramic, which may be due to the variation of coordination environment of Er³⁺ and Yb³⁺ ions after crystallization. The high transparency, intense upconversion luminescence and the simple, low-cost fabrication process make this material exhibiting potential applications in the fields of amorphous silicon solar cells.     

Role of organic molecules on upconversion luminescence of LaF3 nanoparticles

Yb and Er codoped LaF₃ nanocrystals were synthesized and studied. The upconversion luminescence properties of nanocrystals capped with different ligands are mainly dependent on the ligands, especially for the red emission which is sensitive to the nonradiative relaxation. The chelation between the ligands and rare earth ions can affect the morphology and fluorescent properties of samples. The chelating ligands will reduce the nonradiative quenching by isolating the RE ions from surrounding environment. So the upconversion luminescence properties of the samples vary correspondingly.     

One-step synthesis and optical properties of water-soluble and amine-functionalized Dy3+-doped BaFCl nanocrystals

Water-soluble and amino-functionalized luminescent Dy3+-doped BaFCl nanocrystals have been synthesized for the first time via a facile one-step modified solvothermal method with polyethyleneimine (PEI) as capping agent. The obtained BaFCl:Dy3+ nanocrystals have a size of about 40 nm, remain stable in aqueous solutions under different pH, and exhibit intense visible luminescence of Dy3+. The synthesized nanocrystals featuring long-lived luminescence may have potential applications as time-resolved photoluminescent probes for bio-applications.     

稀土上转换发光纳米材料的制备及生物医学应用研究进展

荧光探针技术已经被广泛应用于生物成像、生物标记、生物检测、免疫分析等生物医学领域。传统荧光标记材料,如有机荧光染料、荧光蛋白和半导体量子点,目前面临诸多应用局限,如发光强度不稳定、检测灵敏度低、生物毒性高、自荧光强等。有鉴于此,人们开发了La系金属离子掺杂的稀土上转换发光纳米材料作为新型生物标记材料,该材料受近红外光激发后发出近红外或可见光范围内的高能量光子。这种带有特殊光学性质及良好生物相容性的荧光标记材料克服了传统荧光标记材料的缺点,从而成为材料科学与生物医学交叉领域的研究热点。综述了稀土纳米材料上转换功能的特殊物理机制及其制备和表面修饰方法的研究进展。在此基础上介绍了稀土上转换纳米材料在生物成像、检测、载药、即时诊断器件开发等生物医学工程中的应用。     

Optical downconversion in rare earth (Tb and Yb) doped CdS nanocrystals

CdS host nanocrystals (4.2-5.5 nm in diameter) have been prepared by a low-cost synthetic chemical route using air stable precursors and doped with rare earth (RE) ions, terbium (Tb³⁺) and ytterbium (Yb³⁺). The resulting RE³⁺-doped nanocrystals show a complete broadband absorption below their band edge (400-460 nm) to the deep UV region. CdS host nanocrystals act as an energy receptor and sensitizer for the RE³⁺-ions. A broadband emission in the visible region is observed for the RE³⁺-doped CdS nanocrystals by room temperature photoluminescence (PL) measurements. Our results show that these novel RE³⁺-doped nanocrystals can be used as an optical down-conversion material for solar spectral matching in solar cells or as a wavelength shifting down-converter for nanoscale optoelectronic applications.     

稀土掺杂上转换发光玻璃陶瓷的制备及性能

实验制备了一类含有SrF2∶Yb3+,Tm3+及SrF2∶Yb3+,Er3+的透明发光玻璃和玻璃陶瓷,对比研究了热处理工艺对玻璃陶瓷相组成、微观结构和光谱性能的影响规律。研究表明,玻璃陶瓷具有立方SrF2纳米晶相均匀分布于玻璃基体的复相结构,利用HRTEM可观测到SrF2纳米晶相的(111)晶面,其晶粒尺度在10~30nm之间,且该析晶相中富集有Yb3+/Tm3+和Yb3+/Er3+。基于此,玻璃陶瓷在980nm LD激光激发下的上转换发光强度较玻璃样品有较大提高。其上转换发光机制分别主要为Yb3+-Yb3+之间的合作上转换,Yb3+-Tm3+和Tm3+-Tm3+之间的交叉弛豫能量传递过程,以及Yb3+-Er3+之间的能量传递上转换。     

Upconversion emission of BaTiO<Subscript>3</Subscript>: Er nanocrystals

Here, we report the dopant concentration and pump-power dependence upconversion emission properties of erbium doped BaTiO₃ nanocrystals derived from sol-emulsion-gel method. Green (550 nm) and red (670 nm) upconversion emissions were observed at room temperature from the ⁴ S _3/2 and ⁴ F _9/2 levels of Er³⁺: BaTiO₃ nanocrystals. It is found that at 850 mW of cw excitation power (at 980 nm) the total luminescence was 17130 Cd/m² for 1000°C heated 0.25 mol% Er-doped BaTiO₃ nanocrystals. It is worthwhile to mention that the unusual power-dependent upconversion luminescence (saturation) is observed at higher dopant concentration (2.5 mol%) and high pump power. Our analysis confirms that the depletion of the excited state is responsible for the relevant fluorescence upconversion. We have again confirmed that a twophoton excited state absorption process occurs for all samples.     

Ho3+上转换发光在染料敏化太阳能电池中的应用

以水热和高温煅烧相结合的方法制备了掺Ho3+的TiO2上转换发光层,并将其组装在染料敏化太阳能电池中.通过XRD、荧光光谱仪、UV-vis和电池的光电性能测试,来分析上转换发光层的发光机理及其加入后对染料敏化太阳能电池性能的影响.结果表明,上转换发光层的引入有效地提高了DSSC的光电性能,在80mW/cm2红外光照射下最高光电转换效率达到了0.12‰,比未加上转换发光层的DSSC提高了360%.     

Ultrafast Single‐Band Upconversion Luminescence in a Liquid‐Quenched Amorphous Matrix

Achieving single‐band upconversion is a challenging but rewarding approach to attain optimal performance in diverse applications, such as multiplexed molecular imaging, security coding, and nonlinear photonic devices. Here, highly efficient single‐band upconversion luminescence in the green spectral regime (16.4 times increase in emission at 525 nm) accomplished by realizing minimal energy loss from two‐photon upconversion in a newly synthesized liquid‐quenched amorphous matrix is reported. In contrast to previously reported single‐band upconversion, this phenomenon originates from the elevated transition probability of the host sensitive transition via changes in the host matrix's microstructure. The elevated transition probability facilitates ultrafast decay of upconversion luminescence with decay times as short as 0.2 µs, the fastest decay ever reported. The material in this study therefore has strong potential for use in photonic devices demanding high upconversion efficiency with a fast response time, which to date has been inaccessible using upconversion materials.     

Giant enhancement of upconversion in ultra-small Er³⁺/Yb³⁺:NaYF₄ nanoparticles via laser annealing

Most of the synthesis routes of lanthanide-doped phosphors involve thermal processing which results in nanocrystallite growth, stabilization of the crystal structure and augmentation of luminescence intensity. It is of great interest to be able to transform the sample in a spatially localized manner, which may lead to many applications like 2D and 3D data storage, anti-counterfeiting protection, novel design bio-sensors and, potentially, to fabrication of metamaterials, 3D photonic crystals or plasmonic devices. Here we demonstrate irreversible spatially confined infrared-laser-induced annealing (LIA) achieved in a thin layer of dried colloidal solution of ultra-small ～8 nm NaYF? nanocrystals (NCs) co-doped with 2% Er3? and 20% Yb3? ions under a localized tightly focused beam from a continuous wave 976 nm medium power laser diode excitation. The LIA results from self-heating due to non-radiative relaxation accompanying the NIR laser energy upconversion in lanthanide ions. We notice that localized LIA appears at optical power densities as low as 15.5 kW cm?2 (～354 ± 29 mW) threshold in spots of 54 ± 3 μm diameter obtained with a 10 × microscope objective. In the course of detailed studies, a complete recrystallization to different phases and giant 2-3 order enhancement in luminescence yield is found. Our results are highly encouraging and let us conclude that the upconverting ultra-small lanthanide-doped nanophosphors are particularly promising for direct laser writing applications.     

Improving the Quality and Luminescence Performance of All‐Inorganic Perovskite Nanomaterials for Light‐Emitting Devices by Surface Engineering

Lead halide perovskites and their applications in the optoelectronic field have garnered intensive interest over the years. Inorganic perovskites (IHP), though a novel class of material, are considered as one of the most promising optoelectronic materials. These materials are widely used in detectors, solar cells, and other devices, owing to their excellent charge‐transport properties, high defect tolerance, composition‐ and size‐dependent luminescence, narrow emission, and high photoluminescence quantum yield. In recent years, numerous encouraging achievements have been realized, especially in the research of CsPbX₃ (X = Cl, Br, I) nanocrystals (NCs) and surface engineering. Therefore, it is necessary to summarize the principles and effects of these surface engineering optimization methods. It is also important to scientifically guide the applications and promote the development of perovskites more efficiently. Herein, the principles of surface ligands are reviewed, and various surface treatment methods used in CsPbX₃ NCs as well as quantum‐dot light‐emitting diodes are presented. Finally, a brief outlook on CsPbX₃ NC surface engineering is offered, illustrating the present challenges and the direction in which future investigations are intended to obtain high‐quality CsPbX₃ NCs that can be utilized in more applications.     

NaYF4：Yb,Er红色上转换发光纳米粒子的合成

利用热分解方法在油酸和十八胺的混合溶剂中合成了红色上转换发光的α-NaYF4：Yb,Er纳米粒子,通过X射线衍射（XRD）、透射电镜（TEM）以及980nm激发下的上转换发光光谱等方法进行表征,结果发现,在溶剂油酸和十八胺混合溶剂中,虽然反应时间和温度不同,但产物均为立方相结构且光学性能几乎呈现纯的红色发射光,说明可以在很广泛的范围内合成具有良好的红色上转换发光的NaYF4：Yb,Er纳米粒子。     

Zirconia nanoceramic via redispersion of highly agglomerated nanopowder and spark plasma sintering

A 2.7 mol% yttria stabilizing tetragonal zirconia (2.7Y-TZP) nanopowder was synthesized and stored for five years. Humidity and unsatisfactory storage conditions gradually caused heavy agglomeration. Within a few months, 2.7Y-TZP nanopowder became useless for any technological application. A bead-milling deagglomeration technique was applied to recover the heavily agglomerated yttria-stabilized zirconia nanopowder. Low-temperature sintering and spark plasma sintering (SPS) were performed, resulting in fully dense nanostructured ceramics. Compacts formed with heavily agglomerated powder present low sinterability and poor mechanical properties. Bead-milling suspension formed compacts exhibit mechanical properties in the range of the values reported for nanostructured zirconia. This observation confirms the effectiveness of bead-milling in the deagglomeration of highly agglomerated nanopowders. The high value of Vickers hardness of 13.6 GPa demonstrates the success of the processing technique for recovering long-time-stored oxide nanopowders.     

Er3+ -doped anatase TiO2 nanocrystals: crystal-field levels, excited-state dynamics, upconversion, and defect luminescence

A comprehensive survey of electronic structure and optical properties of rare-earth ions embedded in semiconductor nanocrystals (NCs) is of vital importance for their potential applications in areas as diverse as luminescent bioprobes, lighting, and displays. Er3+ -doped anatase TiO2 NCs, synthesized via a facile sol-gel solvothermal method, exhibit intense and well-resolved intra-4f emissions of Er3+ . Crystal-field (CF) spectra of Er3+ in TiO2 NCs are systematically studied by means of high-resolution emission and excitation spectra at 10-300 K. The CF analysis of Er3+ assuming a site symmetry of C(2v) yields a small root-mean-square deviation of 25.1 cm(-1) and reveals the relatively large CF strength (549 cm(-1) ) of Er3+, thus verifying the rationality of the C(2v) symmetry assignment of Er3+ in anatase TiO2 NCs. Based on a simplified thermalization model for the temperature-dependent photoluminescence (PL) dynamics from (4) S(3/2) , the intrinsic radiative luminescence lifetimes of (4) S(3/2) and (2) H(11/2) are experimentally determined to be 3.70 and 1.73 μs, respectively. Green and red upconversion (UC) luminescence of Er3+ can be achieved upon laser excitation at 974.5 nm. The UC intensity of Er3+ in Yb/Er-codoped NCs is found to be about five times higher than that of Er-singly-doped counterparts as a result of efficient Yb3+ sensitization and energy transfer upconversion (ETU) evidenced by its distinct UC luminescence dynamics. Furthermore, the origin of defect luminescence is revealed based on the temperature-dependent PL spectra upon excitation above the TiO2 bandgap at 325 nm.     

Nanopowders of YAl3(BO3)4 doped by Nd, Yb and Cr obtained by sol-gel method: Synthesis, structure and luminescence properties

Structure, morphology and luminescence properties of nanocrystalline samples of YAl₃(BO₃)₄ (YAB) undoped and doped with neodymium, ytterbium and chromium obtained by the sol-gel method are presented. The best results of synthesis are obtained for mannitol as polymerizing agent. Single phase of nanopowder is obtained for pure YAB. Dopants destroy the compound structure; two other compounds, namely Al₁₈B₄O₃₃ and YBO₃, were revealed by X-ray investigation. Nanopowders show isometric and needles forms, the calculated size of crystallites is about 60 nm. Their optical properties are determined and results are compared to data obtained for single crystal counterparts. It is shown that the influence of rare earth ions incorporated into YBO₃ phase on luminescent spectra and excited state relaxation dynamics of the nanopowders is negligibly small when the YBO₃ content is of the order of several wt%. Residual impurity phases do not affect significantly spectroscopic properties of YAB nanopowders.     

Combinatorial discovery of lanthanide-doped nanocrystals with spectrally pure upconverted emission

Nanoparticles doped with lanthanide ions exhibit stable and visible luminescence under near-infrared excitation via a process known as upconversion, enabling long-duration, low-background biological imaging. However, the complex, overlapping emission spectra of lanthanide ions can hinder the quantitative imaging of samples labeled with multiple upconverting probes. Here, we use combinatorial screening of multiply doped NaYF(4) nanocrystals to identify a series of doubly and triply doped upconverting nanoparticles that exhibit narrow, spectrally pure emission spectra at various visible wavelengths. We then developed a comprehensive kinetic model validated by our extensive experimental data set. Applying this model, we elucidated the energy transfer mechanisms giving rise to spectrally pure emission. These mechanisms suggest design rules for electronic level structures that yield robust color tuning in lanthanide-doped upconverting nanoparticles. The resulting materials will be useful for background-free multicolor imaging and tracking of biological processes.     

Microwave synthesis of yttria stabilized zirconia

Yttria stabilised zirconia (YSZ) nanocrystals, with a mean size between 5 and 10 nm, were prepared by microwave flash synthesis. Flash synthesis was performed in alcoholic solutions of yttrium, zirconium chloride and sodium ethoxide (EtONa) using a microwave autoclave (RAMO system) specially designed by authors. Energy dispersive X-ray analysis (EDX), X-ray powder diffraction (XRD), BET adsorption technique, photon correlation spectroscopy (PCS) transmission and scanning electron microscopy (TEM and SEM) are used to characterized these nanoparticles. Compared with conventional synthesis, nanopowders can be produced in a short period (e.g. 10 s), both high purity and stoechiometric control are obtained. Nevertheless, this mean of production is more cheaper and much faster than the ones commonly used to produce yttria stabilized zirconia (YSZ) by conventional sol-gel techniques.     

Tough yttria-stabilized zirconia ceramic by low-temperature spark plasma sintering of long-term stored nanopowders

Weakly agglomerated 1.75 and 3 mol% yttria stabilized zirconia nanopowders were used in this study after six years of storage in vacuum-processed plastic containers. The proper storage conditions of the Y-TZP nanopowders avoided the hard agglomeration. Untreated and bead-milled nanopowders were used to obtain dense ceramics by slip casting and subsequent low-temperature sintering. Fully dense nanostructured 1.75Y-TZP and 3Y-YZP ceramics with and without doping of 1 wt% Al2O3 were produced by an optimized spark plasma sintering (SPS) technique at the temperatures of 1050-1150 degrees C at a pressure of 100 MPa. The SPS has revealed the clear advantage of consolidation of the weakly agglomerated nanopowders without preliminary deagglomeration. The Vickers hardness of both the low-temperature and spark plasma sintered samples was found to lie in the range of 10.98-13.71 GPa. A maximum fracture toughness of 15.7 MPa m(1/2) (average 14.23 MPa m(1/2)) was achieved by SPS of the 1.75Y-TZP ceramic doped with 1 wt% Al2O3 whereas the toughness of the 3Y-TZP ceramics with and without alumina doping was found to vary between 3.55 and 5.5 MPa m(1/2).