AgGaS_2晶体Ⅱ类非共线相位匹配CO_2激光参量上转换

本文报道了AgGaS_2晶体Ⅱ类非共线相位匹配Q开关Nd:YAG激光泵浦CO_2激光参量上转换研究结果,用迭代法计算了相位失配因子△K=0时的最佳非共线夹角.当泵浦功率密度为6MW/cm~2和晶体长度为4.7mm时,功率转换效率达16.1%,并且首次采用硅雪崩光电二极管接收和频信号.     

Multifunctional Nano‐Bioprobes Based on Rattle‐Structured Upconverting Luminescent Nanoparticles

Lanthanide‐doped upconversion nanoparticles (UCNPs) have shown great promise in versatile bioapplications. For the first time, organosilica‐shelled β‐NaLuF₄:Gd/Yb/Er nanoprobes with a rattle structure have been designed for dual‐modal imaging and photodynamic therapy (PDT). Benefiting from the unique rattle structure and aromatic framework, these nanoprobes are endowed with a high loading capacity and the disaggregation effect of photosensitizers. After loading of β‐carboxyphthalocyanine zinc or rose Bengal into the nanoprobes, we achieved higher energy transfer efficiency from UCNPs to photosensitizers as compared to those with conventional core–shell structure or with pure‐silica shell, which facilitates a large production of singlet oxygen and thus an enhanced PDT efficacy. We demonstrated the use of these nanoprobes in proof‐of‐concept X‐ray computed tomography (CT) and UC imaging, thus revealing the great potential of this multifunctional material as an excellent nanoplatform for cancer theranostics.     

Lanthanide‐Doped Nanocrystals: Strategies for Improving the Efficiency of Upconversion Emission and Their Physical Understanding

The fundamental understanding of lanthanide‐doped upconverted nanocrystals remains a frontier area of research because of potential applications in photonics and biophotonics. Recent studies have revealed that upconversion luminescence dynamics depend on host crystal structure, size of the nanocrystals, dopant concentration, and core–shell structures, which influence site symmetry and the distribution and energy migration of the dopant ions. In this review, we bring to light the influences of doping/co‐doping concentration, crystal phase, crystal size of the host, and core–shell structure on the efficiency of upconversion emission. Furthermore, the lattice strain, due to a change in the crystal phase and by the core–shell structure, strongly influences the upconversion emission intensity. Analysis suggests that the local environment of the ion plays the most significant role in modification of radiative and nonradiative relaxation mechanisms of overall upconversion emission properties. Finally, an outlook on the prospects of this research field is given.     

Tuning the Upconversion Luminescence Lifetimes of KYb2F7:Ho3+ Nanocrystals for Optical Multiplexing

Conventional luminescent color coding is limited by spectral overlap and the interference of background fluorescence, thus restricting the number of distinguishable identities that can be used in practice. Here, we demonstrate the possibility of generating diverse time‐domain codes, specially designed for a single emission band, using lanthanide‐doped upconversion nanocrystals. Based on the knowledge of concentration quenching, the upconversion luminescence kinetics of KYb₂F₇: Ho³⁺ nanocrystals can be precisely controlled by modifying the dopant concentration of Ho³⁺ ions, resulting in a tunable emission lifetime from 75.8 to 1944.5 μs, which suggests the practicality of these time‐domain codes for optical multiplexing.     

Single‐Component Upconverting Polymeric Nanoparticles

Low‐power light upconversion is a highly desirable feature for a broad range of applications and new materials enabling this process are sought in both bulk and particulate form. Here, the preparation of upconverting nanoparticles is reported from a methacrylic terpolymer bearing diphenylanthracene and meso‐phenoxytris(heptyl)porphyrin pendant groups by a microemulsion technique. The use of a terpolymer in which the upconvering dye molecules are covalently attached mitigates some of the drawbacks of triplet–triplet annihilation upconverting nanoparticles made by other techniques, in particular dye leakage from the nanoparticles, and limited control of the sensitizer and emitter concentration within each nanoparticle. Size and morphology of the new upconverting nanoparticles are investigated by dynamic light scattering and transmission electron microscopy and elucidated their upconverting properties by luminescence spectroscopy.

     

Complementary Lock‐and‐Key Ligand Binding of a Triplet Transmitter to a Nanocrystal Photosensitizer

Owing to the difficulty in comprehensively characterizing nanocrystal (NC) surfaces, clear guidance for ligand design is lacking. In this work, a series of bidentate bis(pyridine) anthracene isomers (2,3‐PyAn, 3,3‐PyAn, 2,2‐PyAn) that differ in their binding geometries were designed to find the best complementary fit to the NC surface. The efficiency of triplet energy transfer (TET) from the CdSe NC donor to a diphenylanthracene (DPA) acceptor mediated by these isomers was used as a proxy for the efficacy of orbital overlap and therefore ligand binding. 2,3‐PyAn, with an intramolecular N–N distance of 8.2 Å, provided the best match to the surface of CdSe NCs. When serving as a transmitter for photon upconversion, 2,3‐PyAn yielded the highest upconversion quantum yield (QY) of 12.1±1.3 %, followed by 3,3‐PyAn and 2,2‐PyAn. The TET quantum efficiencies determined by ultrafast transient absorption measurements showed the same trend.     

Stabilization of High Oxidation State Upconversion Nanoparticles by N‐Heterocyclic Carbenes

The stabilization of high oxidation state nanoparticles by N‐heterocyclic carbenes is reported. Such nanoparticles represent an important subset in the field of nanoparticles, with different and more challenging requirements for suitable ligands compared to elemental metal nanoparticles. N‐Heterocyclic carbene coated NaYF₄:Yb,Tm upconversion nanoparticles were synthesized by a ligand‐exchange reaction from a well‐defined precursor. This new photoactive material was characterized in detail and employed in the activation of photoresponsive molecules by low‐intensity near‐infrared light (λ =980 nm).     

Ca2+掺杂对NaYF4:Yb,Er微米晶上转换发光性能的影响

采用柠檬酸钠辅助的水热方法制备了一系列不同Ca²⁺含量的Ca²⁺/Yb³⁺/Er³⁺共掺的NaYF₄微米片。利用透射电子显微镜(TEM)、X射线衍射分析(XRD)、发光光谱等测量手段对样品进行了形貌、晶相、发光性质的表征。样品在980 nm激光泵浦下,可以观察到强的上转换绿色荧光。在Ca²⁺的摩尔分数从0增加到8%的过程中,紫外到可见的上转换发光随着Ca²⁺浓度的增加而显著增强。这是由于Ca²⁺的掺杂导致了晶体内部的不对称性,同时也提高了晶体的结晶性。     

Gd~(3+),Tm~(3+)和Yb~(3+)掺杂的Y_2O_3微晶中Gd~(3+)离子的紫外上转换发光及其增强的研究

采用均相沉淀法制备了Y(OH)3微米颗粒,经1 100℃焙烧后制备出具有上转换发光性质的Yb3+-Tm3+-Gd3+共掺的Y2O3微米晶体,讨论了Yb3+-Tm3+-Gd3+在Y2O3中能量传递过程及壳层对发光强度的影响。980 nm近红外光激发下的上转换光谱表明,在Yb3+-Tm3+-Gd3+共掺Y2O3体系中,核-壳结构大幅提高了Gd3+离子和Tm3+离子的上转换发光强度,尤其是样品在紫外发光部分的增强相比于可见和红外光部分更为明显。同时,通过研究Tm3+和Gd3+在不同波段的发光强度与泵浦功率的关系探讨了氧化物中上转换发光的机制。     

核壳纳米结构壳中Yb离子对稀土上转换发光温度特性的影响

采用油酸盐法分别制备出均匀的上转换发光裸核纳米粒子及其包覆具有不同Yb³⁺浓度掺杂的NaYF₄:Yb³⁺,Er³⁺核壳纳米结构的上转换纳米粒子。在不同温度下(90~450 K),研究分析了在壳中掺杂不同浓度Yb³⁺的NaYF₄:Yb³⁺,Er³⁺@NaYF₄:x%Yb³⁺核壳纳米体系的上转换发光特性。结果表明:在NaYF₄:Yb³⁺,Er³⁺上转换体系中,惰性壳中的525 nm(²H_11/2 →⁴I_15/2)发射峰呈现出与活性壳中不一样的趋势。壳层中掺杂的Yb³⁺通过声子对纳米粒子内部发光与表面及外界之间的相互作用起到了重要的"桥"连作用。