808 nm triggered multifunctional UCNPs@PDA nanocomposites for temperature sensing and photothermal conversion

Multifunctional nanoparticles with marvelous temperature sensing and photothermal conversion are preferable in photothermal therapeutic applications. Herein, nanocomposites of NaYF₄:Er³⁺/Yb³⁺@NaYF₄:Nd³⁺/Yb³⁺ core–shell upconversion nanoparticles (UCNPs) modified by polydopamine (PDA) were designed to achieve temperature sensing and efficiency of photothermal conversion. It has been found that under the irradiation of 808 nm laser, temperature sensing can be realized on the basis of the fluorescence intensity ratio of Er³⁺ green light emission. In addition, the photothermal conversion ability of the UCNPs modified by PDA is greatly improved. Moreover, Nd³⁺ as activator endows UNCPs excited by 808 nm, which can avoid overheating due to the absorption of the excitation band (980 nm) in water. Therefore, the multifunctional nanoparticles are expected to become an effective drug for cancer therapy in the future and this research will stimulate interest in designing multifunctional nanoparticles that are biocompatible, especially for in vivo tumor diagnosis.

     

915 nm Light‐Triggered Photodynamic Therapy and MR/CT Dual‐Modal Imaging of Tumor Based on the Nonstoichiometric Na0.52YbF3.52:Er Upconversion Nanoprobes

Lanthanide (Ln³⁺)‐doped upconversion nanoparticles (UCNPs) as a new generation of multimodal bioprobes have attracted great interest for theranostic purpose. Herein, red emitting nonstoichiometric Na_0.52YbF_3.52:Er UCNPs of high luminescence intensity and color purity are synthesized via a facile solvothermal method. The red UC emission from the present nanophosphors is three times more intense than the well‐known green emission from the ≈30 nm sized hexagonal‐phase NaYF₄:Yb,Er UCNPs. By utilizing Na_0.52YbF_3.52:Er@SrF₂ UCNPs as multifunctional nanoplatforms, highly efficient in vitro and in vivo 915 nm light‐triggered photodynamic therapies are realized for the first time, with dramatically diminished overheating yet similar therapeutic effects in comparison to those triggered by 980 nm light. Moreover, by virtue of the high transverse relaxivity (r ₂) and the strong X‐ray attenuation ability of Yb³⁺ ions, these UCNPs also demonstrate good performances as contrast agents for high contrast magnetic resonance and X‐ray computed tomography dual‐modal imaging. Our research shows the great potential of the red emitting Na_0.52YbF_3.52:Er UCNPs for multimodal imaging‐guided photodynamic therapy of tumors.     

Dual-mode luminescence from lanthanide tri-doped NaYF4 nanocrystals

Silica-coated NaYF₄:Yb/Er(Tm)/Eu nanocrystals (NCs) with a mean size of 35 nm were prepared and characterized. Each of the core/shell NCs can be dispersed in ethanol and water to form stable colloidal solutions and emit bright visible light of two colors (blue and red, green and red) by up- and down-converting excitation modes. As we know, this is the first time to obtain the distinct dual-color photos of NaYF₄:Yb/Er(Tm)/Eu NCs which were dispersed in deionized water. In particular, the ability to optically manipulate luminescence color of NCs doped with RE ions opens the door to multiplexed detection for high precision in more complex biotic environment.     

Luminescence properties and excitation process of a near-infrared to visible up-conversion color-tunable phosphor

Further investigation of previously reported color-tunable NaNbO₃-based up-conversion phosphor doped with Er³⁺, Yb³⁺, and Al³⁺ (NaNbO₃:Er,Yb,Al) was undertaken. Color tuning is achieved by variation of the relative intensity of the red/green emission, which is dependent on the pulse width of the near-infrared (980 nm) excitation. The chromaticity of emissions ranging from green to reddish-yellow with a change of pulse duration from 50 to 2400 μs is wider than that of the reference compound LaGaO₃:Er,Yb, and is not influenced by the excitation intensity. It was elucidated that the green and red emissions occur via different excitation routes, of which the latter is characterized by a much slower build-up of emission.     

Multicolor up conversion emission and color tunability in Yb/Tm/Ho triply doped heavy metal oxide glasses

Multicolor and white light emissions have been achieved in Yb³⁺, Tm³⁺ and Ho³⁺ triply doped heavy metal oxide glasses upon laser excitation at 980 nm. The red (660 nm), green (547 nm) and blue (478 nm) up conversion emissions of the rare earth (RE) ions triply doped TeO₂–GeO₂–Bi₂O₃–K₂O glass (TGBK) have been investigated as a function of the RE concentration and excitation power of the 980 nm laser diode. The most appropriate combination of RE in the TGBK glass host (1.6 wt% Yb₂O₃, 0.6 wt% Tm₂O₃ and 0.1 wt% Ho₂O₃) has been determined with the purpose to tune the primary colors (RGB) respective emissions and generate white light emission by varying the pump power. The involved infrared to visible up conversion mechanisms mainly consist in a three-photon blue up conversion of Tm³⁺ ions and a two-photon green and red up conversions of Ho³⁺ ions. The resulting multicolor emissions have been described according to the CIE-1931 standards.     

Structural and luminescence properties of Ho(3+)/Yb(3+)-doped Lu3Ga5O12 nano-garnets for phosphor applications

Lu3Ga5O12 nano-garnet powders doped with Ho(3+)/Yb(3+) ions have been prepared using a citrate sol-gel technique. The structural and morphological properties have been investigated by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. The materials are found to exist in single phase of cubic garnet structure with an average particle size of around 45 nm. The Ho(3+)/Yb(3+)-doped Lu3Ga5O12 nano-garnet powders give rise to an intense green and weak red emission of Ho3+ ions under 457.5 nm direct excitation. Moreover, when the Yb3+ ions are excited at 950 nm a very bright green luminescence of the Ho3+ ions is observed by the naked eyes even for such low laser power as 10 mW and the intensity of the red emission have been increased compared to that found under direct excitation of the Ho3+ ions. The power dependency and dynamics of the infrared-to-visible upconverted luminescence confirm the existence of different two-photon energy transfer processes. All these results have been compared with those obtained for other garnets doped with similar lanthanide ions which suggest that the Lu3Ga5O12 nano-garnets are potential materials for light emitting devices.     

Lanthanide‐Doped Core@Multishell Nanoarchitectures: Multimodal Excitable Upconverting/Downshifting Luminescence and High‐Level Anti‐Counterfeiting

The development of luminescent materials with concurrent multimodal emissions is a great challenge to improve security and data storage density. Lanthanide‐doped nanocrystals are particularly appropriate for such applications for their abundant intermediate energy states and distinguishable spectroscopic profiles. However, traditional lanthanide luminescent nanoparticles have a limited capacity for information storage or complexity to shield against counterfeiting. Herein, it is demonstrated that the combination of upconverting and downshifting emissions in a particulate designed lanthanide‐doped core@multishell nanoarchitecture allows the generation of multicolor dual‐modal luminescence over a wide spectral range for complex information storage. Precise control of lanthanide dopants distribution in the core and distinct shells enables simultaneous excitation of 980/808 nm focusing/defocusing laser and 254 nm light and produces complex upconverting emissions from Er, Tm, Eu, and Tb via multiphoton energy transfer processes and downshifting emissions from Eu and Tb via efficient energy transfer from Ce to Eu/Tb in Gd‐assisted lattices. It is experimentally proven that multiple visualized anti‐counterfeit and information encryption with facile decryption and authentication using screen‐printing inks containing the present core@multishell nanocrystals are practically applicable by selecting different excitation modes.     

Shaping Luminescent Properties of Yb3+ and Ho3+ Co‐Doped Upconverting Core–Shell β‐NaYF4 Nanoparticles by Dopant Distribution and Spacing

At the core of luminescence color and lifetime tuning of rare earth doped upconverting nanoparticles (UCNPs), is the understanding of the impact of the particle architecture for commonly used sensitizer (S) and activator (A) ions. In this respect, a series of core@shell NaYF₄ UCNPs doped with Yb³⁺ and Ho³⁺ ions are presented here, where the same dopant concentrations are distributed in different particle architectures following the scheme: YbHo core and YbHo@…, …@YbHo, Yb@Ho, Ho@Yb, YbHo@Yb, and Yb@YbHo core–shell NPs. As revealed by quantitative steady‐state and time‐resolved luminescence studies, the relative spatial distribution of the A and S ions in the UCNPs and their protection from surface quenching has a critical impact on their luminescence characteristics. Although the increased amount of Yb³⁺ ions boosts UCNP performance by amplifying the absorption, the Yb³⁺ ions can also efficiently dissipate the energy stored in the material through energy migration to the surface, thereby reducing the overall energy transfer efficiency to the activator ions. The results provide yet another proof that UC phosphor chemistry combined with materials engineering through intentional core@shell structures may help to fine‐tune the luminescence features of UCNPs for their specific future applications in biosensing, bioimaging, photovoltaics, and display technologies.     

Paramagnetism and improved upconversion luminescence properties of NaYF4:Yb,Er/NaGdF4 nanocomposites synthesized by a boiling water seed-mediated route

In a route boiling water served as reaction medium, a stoichiometric amount of rare-earth compound and fluoride are put into this system to form α-NaYF₄:Yb, Er nuclei. Then prepared sample is heated at elevated temperature to improve the fluorescence intensity, and next a NaGdF₄ shell grows on the surface of NaYF₄ nuclei. NaYF₄:Yb,Er/NaGdF₄ core–shell structured upconversion nanoparticles (CSUCNPs) have been successfully synthesized by above route. The use of boiling water decreases the cubic-to-hexagonal phase transition temperature of NaYF₄:Yb,Er to 350°C and increases its upconversion (UC) luminescence intensity. A heterogeneous NaGdF₄ epitaxially growing on the surface of Ln³⁺-doped NaYF₄ not only improves UC luminescence, but also creates a paramagnetic shell, which can be used as contrast agents in magnetic resonance imaging (MRI). The solution of CSUCNPs shows bright green UC fluorescence under the excitation at 980 nm in a power density only about 50 mW·cm^–2. A broad spectrum with a dominant resonance at g of about 2 is observed by the electron paramagnetic resonance (EPR) spectrum of CSUCNPs. Above properties suggest that the obtained CSUCNPs could be potential candidates for dual-mode optical/magnetic bioapplications.     

Up-conversion luminescence in Er/Yb-codoped PbTiO3 perovskite obtained via Pechini method

Efficient infrared-to-visible conversion by Er³⁺/Yb³⁺-codoped PbTiO₃ perovskite will be reported. The process is observed under 980 nm laser diode (GaAs:Si) excitation and results in the generation of green (∼555 nm) and red (∼655 nm) emission. The main mechanism that allows for up-conversion is attributed the energy transfer among Yb and Er ions in excited states. The power up-conversion efficiency for red emission is predominant in this material. The results illustrate the large potential of this new class of material for photonic applications involving optoelectronics devices.     

Cr3+-Yb3+-Er3+共掺杂NaYF4微管的制备及上转换发光

利用水热法制备了Cr~(3+)-Yb~(3+)-Er~(3+)共掺杂的NaYF_4微管。在980nm的红外激光激发下,微管产生了强的可见上转换荧光。相比于Yb~(3+)-Er~(3+)共掺NaYF4微棒,微管的绿光和红光强度分别提高30倍及20倍。上转换荧光增强的原因被归结为Cr~(3+)掺入引起稀土离子周围晶体场对称性的减弱。对微管的生长过程及上转换发光机制进行了分析。     

Albumin Nanoshell Encapsulation of Near‐Infrared‐Excitable Rare‐Earth Nanoparticles Enhances Biocompatibility and Enables Targeted Cell Imaging

The use of traditional fluorophores for in vivo imaging applications is limited by poor quantum yield, poor tissue penetration of the excitation light, and excessive tissue autofluorescence, while the use of inorganic fluorescent particles that offer a high quantum yield is frequently limited due to particle toxicity. Rare‐earth‐doped nanoparticles that utilize near‐infrared upconversion overcome the optical limitations of traditional fluorophores, but are not typically suitable for biological application due to their insolubility in aqueous solution, lack of functional surface groups for conjugation of biomolecules, and potential cytotoxicity. A new approach to establish highly biocompatible and biologically targetable nanoshell complexes of luminescent rare‐earth‐doped NaYF₄ nanoparticles (REs) excitable with 920–980 nm near‐infrared light for biomedical imaging applications is reported. The approach involves the encapsulation of NaYF₄ nanoparticles doped with Yb and Er within human serum albumin nanoshells to create water‐dispersible, biologically functionalizable composite particles. These particles exhibit narrow size distributions around 200 nm and are stable in aqueous solution for over 4 weeks. The albumin shell confers cytoprotection and significantly enhances the biocompatibility of REs even at concentrations above 200 µg REs mL^?1. Composite particles conjugated with cyclic arginine‐glycine‐aspartic acid (cRGD) specifically target both human glioblastoma cell lines and melanoma cells expressing α_vβ₃ integrin receptors. These findings highlight the promise of albumin‐encapsulated rare‐earth nanoparticles for imaging cancer cells in vitro and the potential for targeted imaging of disease sites in vivo.     

Binary Nanoparticle Superlattices for Plasmonically Modulating Upconversion Luminescence

Engineering a facile and controllable approach to modulate the spectral properties of lanthanide‐doped upconversion nanoparticles (UCNPs) is always an ongoing challenge. Herein, long‐range ordered, distinct two‐dimensional (2D) binary nanoparticle superlattices (BNSLs) composed of NaREF₄:Yb/Er (RE = Y and Gd) UCNPs and plasmonic metallic nanoparticles (Au NPs), including AB, AB₃, and AB₁₃ lattices, are fabricated via a slow evaporation‐driven self‐assembly to achieve plasmonic modulation of upconversion luminescence (UCL). Optical measurements reveal that typical red–green UCL from UCNPs can be effectively modulated into reddish output in BNSLs, with a drastically shortened lifetime. Notably, for AB₃‐ and AB₁₃‐type BNSLs with more proximal Au NPs around each UCNP, modified UCL with fine‐structured spectral lineshape is observed. These differences could be interpreted by the interplay of collective plasmon resonance introduced by 2D periodic Au arrays and spectrally selective energy transfer between UCNPs and Au. Thus, fabricating UCNP‐Au BNSLs with desired lattice parameters and NP configurations could be a promising way to tailor the UCL through controlled plasmonic modulation.     

Bi/Tm共掺TiO2-BaO-SiO2-Ga2O3玻璃光谱特性与能量转换机理研究

用高温熔融法制备了Bi、Tm、Bi/Tm掺杂TiO₂-BaO-SiO₂-Ga₂O₃玻璃系统。在808 nm激光激发下, 与Tm单掺杂玻璃相比, Bi/Tm共掺玻璃中Tm³⁺的³H₄→³F₄跃迁荧光(~1485 nm)得到了显著的增强, 而Tm³⁺的³F₄→³H₆跃迁荧光(~1810 nm)减弱。在980 nm激光激发下, Tm单掺玻璃中没有观察到Tm离子的特征发光, 而在Bi/Tm共掺玻璃中观察到Tm³⁺的³F₄→³H₆跃迁荧光(~1810 nm)。这是由于在808和980 nm激光二极管(LD)各自激发下, Bi/Tm共掺玻璃中活性Bi离子的近红外发光能量传递给Tm³⁺, 分别产生³F₄→³H₄与³H₆→³H₅跃迁所致。采用Inokuti-Hirayama模型, 分析了该玻璃体系中Bi→Tm的能量传递机理。结果表明, Bi→Tm的能量传递属于电偶极–偶极相互作用。     

Investigation on Yb3+∕Er3+∕Tm3+ tri-doped phosphate glass ceramic for white-light-emitting diode

Yb3+∕Er3+∕Tm3+ tri-doped phosphate glass ceramics were prepared by a high-temperature melting method and thermal treatment technology. Upconversion (UC) emissions of the Yb3+∕Er3+∕Tm3+ tri-doped phosphate glass ceramic samples were studied under 975 nm excitation. The glass ceramic samples can simultaneously generate blue, green, and red emissions. The multicolor emission obtained was tuned to white light by adjusting the Er3+ ion concentration. The emission color of the sample doped with 8 mol.% Er3+ ion is white to the naked eye, and CIE coordinates (x=0.316, y=0.354) of the sample are close to the standard equal energy white-light illumination (x=0.333, y=0.333). The material will be useful in developing the white-light-emitting diode.     

Preparation and upconversion luminescence of Y2SiO5:Yb3+, Ho3+ nanophosphors

X1 type monoclinic Y2SiO5:Yb3+, Ho3+ nanophosphors with fixed (varied) Ho3+ and varied (fixed) Yb3+ concentrations were synthesized by sol-gel method. The nanophosphors presented lacunaris shape with an average size of about 47 nm measured by transmission electron microscopy and scanning electron microscopy. Up-conversion emissions have been observed at 550 nm corresponding to (5F4, 5S2)-5I8 transition and 661 nm due to 5F5-5I8 transition of Ho3+ upon 980 nm excitation at room temperature. The results indicate that both green and red luminescences are based on the two-photon process through the energy transfer from Yb3+. However, the intensity of green emission is weaker than that of the red, because the 5I7 level of Ho3+ can be effectively populated. The integrated upconversion emission intensity on the Yb3+ and Ho3+ concentrations were also studied.     

Red‐Emitting Upconverting Nanoparticles for Photodynamic Therapy in Cancer Cells Under Near‐Infrared Excitation

Upconverting nanoparticles (UCNPs) have attracted considerable attention as potential photosensitizer carriers for photodynamic therapy (PDT) in deep tissues. In this work, a new and efficient NIR photosensitizing nanoplatform for PDT based on red‐emitting UCNPs is designed. The red emission band matches well with the efficient absorption bands of the widely used commercially available photosensitizers (Ps), benefiting the fluorescence resonance energy transfer (FRET) from UCNPs to the attached photosensitizers and thus efficiently activating them to generate cytotoxic singlet oxygen. Three commonly used photosensitizers, including chlorine e6 (Ce6), zinc phthalocyanine (ZnPc) and methylene blue (MB), are loaded onto the alpha‐cyclodextrin‐modified UCNPs to form Ps@UCNPs complexes that efficiently produce singlet oxygen to kill cancer cells under 980 nm near‐infrared excitation. Moreover, two different kinds of drugs are co‐loaded onto these nanoparticles: chemotherapy drug doxorubicin and PDT agent Ce6. The combinational therapy based on doxorubicin (DOX)‐induced chemotherapy and Ce6‐triggered PDT exhibits higher therapeutic efficacy relative to the individual means for cancer therapy in vitro.     

Effect of Yb concentration on the upconversion of Er ion doped La2O3 nanocrystals under 980 nm excitation

The effect of Yb³⁺ concentration on the upconversion of La₂O₃:Yb³⁺, Er³⁺ nanocrystals was reported. Green (about at 530 and 549 nm) and red (around at 672 nm) upconversion emissions under 980 nm excitation were observed at room temperature. It was found that the ratio of green to red upconversion emission intensity is considered as a function of Yb³⁺ ion concentration. Of the samples doped with varying Er³⁺ or constant Er³⁺ ion concentration, it can be observed that the intensity ratio drastically decreases with an Yb³⁺ ion concentration increase and the Yb³⁺ ions concentration is around 3 mol% as the emission intensity ratio of green to red upconversion is close to 1.     

Upconversion luminescence of holmium and ytterbium co-doped yttrium oxysulfide phosphor

The upconversion optical characteristic and brightness of Y₂O₂S:Yb,Ho phosphors are investigated. It is shown that Y₂O₂S:Yb,Ho exhibits NIR, red, green, blue and even ultraviolet-blue emission bands under 980 nm pumping. Moreover, Y₂O₂S:Yb,Ho shows excellent upconversion luminescence and its upconversion brightness is 2.2 times to that of the commercial Y₂O₂S:Yb,Er phosphors. The upconversion mechanism is discussed: the green and NIR emissions are due to two consecutive energy transfer from Yb³⁺ to Ho³⁺, and the blue and red emissions can be explained as a loop-like mechanism.     

White luminescence by up-conversion from thin film made with Ln(3+)-doped NaYF4 nanoparticles

White light-emitting thin films containing Ln(3+)-doped NaYF4 nanoparticles were prepared by a simple spin-coating method. White light was generated by two different lanthanide ions, Er3+ (red and green) and Tm3+ (blue), by upconversion process under the excitation of a 980-nm laser diode. The ratio of the intensity of the three main emissions was tuned by controlling the concentration of the nanoparticles in the thin film and the concentration of the lanthanide ions in the nanoparticles. The color coordinates corresponding to emissions of different nanoparticle concentrations and with the different pump powers were investigated. When the pump power was fixed at 900 mW, the thin film with a concentration ratio of 2.5:1 emitted pure white light with coordinates of (0.333, 0.339).