Controllable Red,Green, Blue (RGB) and Bright White Upconversion Luminescence of Lu2O3:Yb3+/Er3+/Tm3+ Nanocrystals through Single Laser Excitation at 980 nm

Light fantastic! Lu₂O₃:Yb³⁺/Er³⁺/Tm³⁺ nanocrystals with controllable red, green, blue (RGB) and bright white upconversion luminescence by a single laser excitation of 980 nm have been successfully synthesized (see picture). Due to abundant UC PL colors, it can potentially be used as fluorophores in the field of color displays, back light, UC lasers, photonics, and biomedicine.

     

Highly Intensified Upconversion Luminescence of Ca2+‐doped Yb/Er:NaGdF4 Nanocrystals Prepared by a Solvothermal Route

Upon introducing Ca²⁺ dopants into the grain lattices by substituting Gd³⁺ ions, irregular Yb/Er:NaGdF₄ nanocrystals prepared through a simple solvothermal route convert into highly uniform nanorods. Meanwhile, their upconversion luminescence intensifies by about 200 times, probably due to a modification of the crystal structure of NaGdF₄ and an improvement in the crystallinity of the nanophase.     

Synthesis of 10 nm β‐NaYF4:Yb,Er/NaYF4 Core/Shell Upconversion Nanocrystals with 5 nm Particle Cores

A new method is presented for preparing gram amounts of very small core/shell upconversion nanocrystals without additional codoping of the particles. First, ca. 5 nm β‐NaYF₄:Yb,Er core particles are formed by the reaction of sodium oleate, rare‐earth oleate, and ammonium fluoride, thereby making use of the fact that a high ratio of sodium to rare‐earth ions promotes the nucleation of a large number of β‐phase seeds. Thereafter, a 2 nm thick NaYF₄ shell is formed by using 3–4 nm particles of α‐NaYF₄ as a single‐source precursor for the β‐phase shell material. In contrast to the core particles, however, these α‐phase particles are prepared with a low ratio of sodium to rare‐earth ions, which efficiently suppresses an undesired nucleation of β‐NaYF₄ particles during shell growth.     

Tm3+/Yb3+掺杂亚碲酸盐玻璃蓝红光上转换的研究

研究了掺Tm^3 /Yb^3 亚碲酸盐玻璃室温下的上转换发光。用970nm波长的半导体激光器作为泵浦源，得到了高效率的480nm波长上转换的荧光，通过对不同掺杂浓度样品的发光比较，发现了这种玻璃上转换发光的浓度猝灭现象，找出了这种玻璃得到高效率上转换发光的适宜浓度，并对Tm^3 的浓度猝灭现象进行了分析，通过对上转换发光强度与泵浦强度关系曲线的拟合，看到这种上转换是三光子吸收过程，这与通过能级图分析得到的结果相同，另外，也对650nm波长的转换发光进行了研究。     

不同形貌Er,Yb共掺六方NaYF4的合成及上转换发光特性研究

利用水热法成功合成了不同形貌的稀土掺杂六方NaY0.95Yb0.03Er0.02F4,包括柱状、粒状、片状、管状等.通过XRD,SEM,TEM对合成样品的物相结构及晶粒形态进行了表征,探讨络合剂EDTA用量;表面活性剂CTAB,P123,十二烷基苯磺酸钠;热溶剂水、乙二醇、聚乙二醇对晶体生长方向的影响,并对不同形态样品进行上转换发光性能测试,分析晶粒形态对上转换发光强度与寿命的影响,结果显示晶粒越小发光强度越强,相当粒径的管状样品的发光强度比粒状的强,不同晶粒形态上转换的主要能量传递模式也不相同.研究结果可以指导我们可控合成适应实际应用需求的晶粒形态及优良上转换发光性能的材料.     

Intense Upconversion Luminescence of CaSc2O4:Ho3+/Yb3+ from Large Absorption Cross Section and Energy‐Transfer Rate of Yb3+

Concentration‐optimized CaSc₂O₄:0.2 % Ho³⁺/10 % Yb³⁺ shows stronger upconversion luminescence (UCL) than a typical concentration‐optimized upconverting phosphor Y₂O₃:0.2 % Ho³⁺/10 % Yb³⁺ upon excitation with a 980 nm laser diode pump. The ⁵F₄+⁵S₂→⁵I₈ green UCL around 545 nm and ⁵F₅→⁵I₈ red UCL around 660 nm of Ho³⁺ are enhanced by factors of 2.6 and 1.6, respectively. On analyzing the emission spectra and decay curves of Yb³⁺: ²F_5/2→²F_7/2 and Ho³⁺: ⁵I₆→⁵I₈, respectively, in the two hosts, we reveal that Yb³⁺ in CaSc₂O₄ exhibits a larger absorption cross section at 980 nm and subsequent larger Yb³⁺: ²F_5/2→Ho³⁺: ⁵I₆ energy‐transfer coefficient (8.55×10^?17 cm³ s^?1) compared to that (4.63×10^?17 cm³ s^?1) in Y₂O₃, indicating that CaSc₂O₄:Ho³⁺/Yb³⁺ is an excellent oxide upconverting material for achieving intense UCL.     

Cooperative near-IR to visible photon upconversion in Yb3+-doped MnCl2 and MnBr2: comparison with a series of Yb3+-doped Mn2+ halides

Yb3+-doped MnCl2 and MnBr2 crystals exhibit strong red upconversion luminescence under near-infrared excitation around 10 000 cm(-1) at temperatures below 100 K. The broad red luminescence band is centred around 15 200 cm(-1) for both compounds and identified as the Mn2+ 4T1g-->6A1g transition. Excitation with 10 ns pulses indicates that the upconversion process consists of a sequence of ground-state and excited-state absorption steps. The experimental VIS/NIR photon ratio at 12 K for an excitation power of 191 mW focused on the sample with a 53 mm lens is 4.1% for MnCl2:Yb3+ and 1.2% for MnBr2:Yb3+. An upconversion mechanism based on exchange coupled Yb3+-Mn2+ ions is proposed. Similar upconversion properties have been reported for RbMnCl3:Yb3+, CsMnCl3:Yb3+, CsMnBr3:Yb3+, RbMnBr3:Yb3+, Rb2MnCl4:Yb3+. The efficiency of the upconversion process in these compounds is strongly dependent on the connectivity between the Yb3+ and Mn2+ ions. The VIS/NIR photon ratio decreases by three orders of magnitude along the series of corner-sharing Yb3+-Cl--Mn2+, edge-sharing Yb3+-(Cl-)2-Mn2+ to face-sharing Yb3+-(Br-)3-Mn2+ bridging geometry. This trend is discussed in terms of the dependence of the relevant super-exchange pathways on the Yb(3+)-Mn2+ bridging geometry.     

Color Point Tuning in Lu3−x−yMnxAl5−xSixO12:yCe3+ for White LEDs

A series of the solid‐solution phosphors Lu_3?x?yMn_xAl_5?xSi_xO₁₂:yCe³⁺ is synthesized by solid‐state reaction. The obtained phosphors possess the garnet structure and exhibit similar excitation properties as the phosphor Lu₃Al₅O₁₂:Ce³⁺, but with an effectively improved red component in the emission spectrum. This can be attributed to the energy transfer from Ce³⁺ to Mn²⁺. Our investigation reveals that electric dipole–quadrupole interactions dominate the energy‐transfer mechanism and that the critical distance determined by the spectral overlap method is about 9.21 Å. The color‐tunable emissions of the Lu_3?x?yMn_xAl_5?xSi_xO₁₂:yCe³⁺ phosphor as a function of Mn₃Al₂Si₃O₁₂ content are realized by continuously shifting the chromaticity coordinates from (0.354, 0.570) to (0.462, 0.494). They indicate that the obtained material may have potential application as a blue radiation‐converting phosphor for white LEDs with high‐quality white light.     

LaF_3∶Yb~(3+),Er~(3+)纳米晶:溶剂热法合成及上转换发光性质

利用溶剂热合成方法,分别以油酸和油胺为表面有机配体,合成了具有六角结构,颗粒尺寸分别为19和23nm单分散的LaF3:Yb3+,Er3+纳米晶。在980nm红外激光照射下,LaF3:Yb3+,Er3+纳米晶发射出肉眼可观察的绿色和红色上转换荧光,而且其发光过程均符合双光子过程。结合红外光谱与上转换光谱分析了表面有机配体对LaF3:Yb3+,Er3+纳米晶上转换发光的影响,结果显示,以油酸分子为表面配体的纳米晶具有较高的上转换发射强度,但以油胺为表面配体的纳米晶的红光发射相对增强。     

Rare‐Earth‐Based Nanoparticles with Simultaneously Enhanced Near‐Infrared (NIR)‐Visible (Vis) and NIR‐NIR Dual‐Conversion Luminescence for Multimodal Imaging

Multifunctional NaGdF₄:Yb³⁺,Er³⁺,Nd³⁺@NaGdF₄:Nd³⁺ core–shell nanoparticles (called Gd:Yb³⁺,Er³⁺,Nd³⁺@Gd:Nd³⁺ NPs) with simultaneously enhanced near‐infrared (NIR)‐visible (Vis) and NIR‐NIR dual‐conversion (up and down) luminescence (UCL/DCL) properties were successfully synthesized. The resulting core–shell NPs simultaneously emitted enhanced UCL at 522, 540, and 660 nm and DCL at 980 and 1060 nm under the excitation of a 793 nm laser. The enhanced UCL and DCL can be explained by complex energy‐transfer processes, Nd³⁺→Yb³⁺→Er³⁺ and Nd³⁺→Yb³⁺, respectively. The effects of Nd³⁺ concentration and shell thickness on the UCL/DCL properties were systematically investigated. The UCL and DCL properties of NPs were observed under the optimal conditions: a shell Nd³⁺ content of 20 % and a shell thickness of approximately 5 nm. Moreover, the Gd:Yb³⁺,Er³⁺,Nd³⁺@Gd:20 % Nd³⁺ NPs exhibited remarkable magnetic resonance imaging (MRI) properties similar to that of a clinical agent, Omniscan. Thus, the core–shell NPs with excellent UCL/DCL/magnetic resonance imaging (MRI) properties have great potential for both in vitro and in vivo multimodal bioimaging.     

Synthesis,properties and mechanism of photodegradation of core–shell structured upconversion luminescent NaYF4:Yb3+,Er3+@BiOCl

Microspherical bismuth oxychloride (BiOCl) can only utilize ultraviolet (UV) light to promote photocatalytic reactions. To overcome this limitation, a uniform and thin BiOCl nanosheet was synthesized with a particle size of about 200 nm. As results of UV–visible diffuse reflectance spectroscopy showed, the band gap of this nanostructure was reduced to 2.78 eV, indicating that the BiOCl nanosheet could absorb and utilize visible light. Furthermore, the upconversion material NaYF₄ doped with rare earth ions Yb³⁺ and Er³⁺ emitted visible light at 410 nm following excitation with near‐infrared (NIR) light (980 nm), which could be utilized by BiOCl to produce a photocatalytic reaction. To produce a high‐efficiency photocatalyst (NaYF₄:Yb³⁺,Er³⁺@BiOCl), BiOCl‐loaded NaYF₄:Yb³⁺,Er³⁺ was successfully synthesized via a simple two‐step hydrothermal method. The as‐synthesized material was confirmed using X‐ray diffraction, scanning electron microscopy, X‐ray photoelectron spectroscopy as well as other characterizations. The removal ratio of methylene blue by NaYF₄:Yb³⁺,Er³⁺@BiOCl was much higher than that of BiOCl alone. Recycling experiments verified the stability of NaYF₄:Yb³⁺,Er³⁺@BiOCl, which demonstrated excellent adsorption, strong visible‐light absorption and high electron–hole separation efficiency. Such properties are expected to be useful in practical applications, and a further understanding of the NIR‐light‐responsive photocatalytic mechanism of this new catalytic material would be conducive to improving its structural design and function.     

Strong Stokes and Upconversion Luminescence from Ultrasmall Ln3+‐Doped BiF3 (Ln=Eu3+, Yb3+/Er3+) Nanoparticles Confined in a Polymer Matrix

Heavy metal fluorides like BiF₃ as a host for lanthanide ions are of interest as bismuth is the only heavy metal that is nontoxic. In this work, we report the synthesis of highly water‐dispersible ultrasmall BiF₃ nanoparticles about 6 nm in size within a poly(vinyl pyrrolidone) matrix by a hydrothermal method. Microscopy analysis reveals that the nanoparticles are well separated and confined within the polymer network. These nanoparticles were found to be excellent hosts for lanthanide (Ln³⁺) ions. Through suitable Ln³⁺ doping, BiF₃ exhibits strong emissions in the visible region upon both UV and near infrared (NIR) excitations. The non‐toxicity of both bismuth and PVP can be advantageous for the potential use of BiF₃ nanoparticles in drug delivery and bioimaging.     

Bi3+‐Er3+ and Bi3+‐Yb3+ Codoped Cs2AgInCl6 Double Perovskite Near‐Infrared Emitters

Bi³⁺ and lanthanide ions have been codoped in metal oxides as optical sensitizers and emitters. But such codoping is not known in typical semiconductors such as Si, GaAs, and CdSe. Metal halide perovskite with coordination number 6 provides an opportunity to codope Bi³⁺ and lanthanide ions. Codoping of Bi³⁺ and Ln³⁺ (Ln=Er and Yb) in Cs₂AgInCl₆ double perovskite is presented. Bi³⁺‐Er³⁺ codoped Cs₂AgInCl₆ shows Er³⁺ f‐electron emission at 1540 nm (suitable for low‐loss optical communication). Bi³⁺ codoping decreases the excitation (absorption) energy, such that the samples can be excited with ca. 370 nm light. At that excitation, Bi³⁺‐Er³⁺ codoped Cs₂AgInCl₆ shows ca. 45 times higher emission intensity compared to the Er³⁺ doped Cs₂AgInCl₆. Similar results are also observed in Bi³⁺‐Yb³⁺ codoped sample emitting at 994 nm. A combination of temperature‐dependent (5.7 K to 423 K) photoluminescence and calculations is used to understand the optical sensitization and emission processes.     

Stimuli‐Responsive Dual‐Color Photon Upconversion: A Singlet‐to‐Triplet Absorption Sensitizer in a Soft Luminescent Cyclophane

Reversible emission color switching of triplet–triplet annihilation‐based photon upconversion (TTA‐UC) is achieved by employing an Os complex sensitizer with singlet‐to‐triplet (S‐T) absorption and an asymmetric luminescent cyclophane with switchable emission characteristics. The cyclophane contains the 9,10‐bis(phenylethynyl)anthracene unit as an emitter and can assemble into two different structures, a stable crystalline phase and a metastable supercooled nematic phase. The two structures exhibit green and yellow fluorescence, respectively, and can be accessed by distinct heating/cooling sequences. The hybridization of the cyclophane with the Os complex allows near‐infrared‐to‐visible TTA‐UC. The large anti‐Stokes shift is possible by the direct S‐T excitation, which dispenses with the use of a conventional sequence of singlet–singlet absorption and intersystem crossing. The TTA‐UC emission color is successfully switched between green and yellow by thermal stimulation.     

In3+共掺杂诱导NaY0.95-xYb0.03Er0.02F4相转变与上转换发光增强研究

引入In³⁺作为新的掺杂离子通过水热法合成了In³⁺与Er³⁺,Yb³⁺共掺杂的NaYF₄上转换发光材料. 通过XRD表征及Rietveld精修,SEM以及TEM研究了In掺杂引起的NaYF₄形貌与晶体结构的变化. 通过发射光谱与发光衰减曲线表征了掺杂NaYF₄的上转换发光性能,以研究晶体微观结构与上转换发光性能之间的关系. 结果表明随着In掺杂量的增加,立方相NaYF₄的晶格畸变不断增强且发生由立方相向六方相的转变. 对于六方相NaYF₄,其上转换发光强度随着In含量的提高不断增强并当In含量为3%时达到最大值. 该研究结果可以有助于设计与合成具有优良上转换发光性能的材料.     

Cr3+:SrGa12O19: A Broadband Near‐Infrared Long‐Persistent Phosphor

Cr³⁺‐doped SrGa₁₂O₁₉ is demonstrated to be a broadband near‐infrared (650–950 nm) long‐persistent phosphor whose luminescence can last for more than 2 h after ultraviolet irradiation is stopped. Detailed analysis of the photoluminescence and thermoluminescence spectra and of the persistent decay behavior of the Cr³⁺‐doped SrGa₁₂O₁₉ samples indicate that the persistent energy transfer from the SrGa₁₂O₁₉ host to the Cr³⁺ ions and the filling and release of electrons into and from the shallow and deep traps through the conduction band is responsible for the long‐persistent phosphorescence.     

Upconversion luminescence and ratiometric temperature sensing behavior of Er3+/Yb3+-codoped CaY2Ge3O10 germanate

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Charge‐transfer‐to‐solvent absorption spectra of I−(H2O)3–5 at a finite temperature via simulation

Ground‐state equilibrium Born–Oppenheimer molecular dynamics on I^?(H₂O)_3–5 clusters at ～200 K are performed to sample configurations for calculating the charge‐transfer‐to‐solvent (CTTS) absorption spectra for these clusters. When there are more water molecules in clusters, the calculated CTTS spectra are found to become more intense with the absorption maxima shifting to higher energies, which is in agreement with experimental results. In addition, compared with the findings for optimized structures, the absorption energies of the iodide 5p orbitals are red‐shifted at ～200 K because, on average, the distances between the iodide and the dangling hydrogen atoms are increased at finite temperatures which weakens the interactions between the iodide and water molecules in the clusters. Moreover, the number of ionic hydrogen bonds in the clusters are also reduced. However, it is found that all dangling hydrogen atoms must be considered to obtain a good correlation between the CTTS excitation energy and the average distance between the iodide and the dangling hydrogen atoms, which indicates the existence of the strong interactions of the CTTS electron with all of the dangling hydrogen atoms.     

Spectroscopic Properties and Upconversion Studies in Ho3+/Yb3+ Co‐doped Calcium Scandate with Spectrally Pure Green emission

The optical properties of a Ho³⁺/Yb³⁺ co‐doped CaSc₂O₄ oxide material are investigated in detail. The spectral properties are described as a function of doping concentrations. The efficient Yb³⁺→Ho³⁺ energy transfer is observed. The transfer efficiency approaches 50 % before concentration quenching. The concentration‐optimized sample exhibits a strong green emission accompanied with a weak red emission, showing perfect green monochromaticity. The results of the spectral distribution, power dependence, and lifetime measurements are presented. The green, red, and near‐infrared (NIR) emissions around 545, 660, and 759 nm are assigned to the ⁵F₄+⁵S₂→⁵I₈, ⁵F₅→⁵I₈, and ⁵F₄+⁵S₂→⁵I₇ transitions of Ho³⁺, respectively. The detailed study reveals the upconversion luminescence mechanism involved in a novel Ho³⁺/Yb³⁺ co‐doped CaSc₂O₄ oxide material.