Xueyuan Chen

A Strategy to Achieve Efficient Dual‐Mode Luminescence of Eu3+ in Lanthanides Doped Multifunctional NaGdF4 Nanocrystals

Trivalent lanthanide (Ln 3 + ) ions doped luminescent nanocrystals (NCs) of various compositions, albeit most of their bulk counterparts have been well studied previously, have attracted reviving interest and come to the forefront in nanophotonics owing to their distinct electrical, optical and magnetic properties as well as their potential applications in diverse fi elds such as LEDs, lasers, biological labeling and imaging. [ 1 ] Compared to conventional luminescent materials such as organic fl uorescent dyes and quantum dots (QDs), these Ln 3 + doped NCs show more superior features including narrow emission band widths ( < 10 nm), [ 2 ] long luminescence lifetime ( μ s–ms range) [ 2b,c ] and low long-term toxicity. [ 3 ] These features coupled with the higher resistance to photobleaching relative to that of organic fl uorescent dyes make them highly suitable for use as alternatives to organic fl uorescent dyes and QDs for various biological applications. In particular, inorganic fl uorides have the advantages of high chemical stability and intrinsic low phonon energies ( ∼ 350 cm − 1 ), and thereby are often employed as host materials for the doping of Ln 3 + to achieve the desirable downconversion (DC) or upconversion (UC) luminescence of Ln 3 + . [ 4 ] Because of well-established effi cient UC luminescence, considerable efforts have been devoted to the synthesis and multicolor tuning of Ln 3 + -doped NaYF 4 UC NCs, where Yb 3 + acting as the sensitizer with a large absorption cross-section at ∼ 980 nm is usually codoped along with the most common UC activator ions (Er 3 + , Tm 3 + and Ho 3 + ) to produce strong red, green, and violet UC emissions. [ 5 ]

Highly efficient non-rare-earth red emitting phosphor for warm white light-emitting diodes

Mn(4+)-activated fluoride compounds, as an alternative to commercial (oxy)nitride phosphors, are emerging as a new class of non-rare-earth red phosphors for high-efficacy warm white LEDs. Currently, it remains a challenge to synthesize these phosphors with high photoluminescence quantum yields through a convenient chemical route. Herein we propose a general but convenient strategy based on efficient cation exchange reaction, which had been originally regarded only effective in synthesizing nano-sized materials before, for the synthesis of Mn(4+)-activated fluoride microcrystals such as K2TiF6, K2SiF6, NaGdF4 and NaYF4. Particularly we achieve a photoluminescence quantum yield as high as 98% for K2TiF6:Mn(4+). By employing it as red phosphor, we fabricate a high-performance white LED with low correlated colour temperature (3,556 K), high-colour-rendering index (Ra=81) and luminous efficacy of 116 lm W(-1). These findings show great promise of K2TiF6:Mn(4+) as a commercial red phosphor in warm white LEDs, and open up new avenues for the exploration of novel non-rare-earth red emitting phosphors.

Amine-Functionalized Lanthanide-Doped KGdF4 Nanocrystals as Potential Optical/Magnetic Multimodal Bioprobes

Amine-functionalized lanthanide-doped KGdF(4) nanocrystals, synthesized via a facile one-step solvothermal route by employing polyethylenimine as the surfactant and capping ligand, have been demonstrated to be sensitive time-resolved FRET bioprobes to detect a trace amount of biomolecules such as avidin at a concentration of 5.5 nM and to be potential T(1)-MRI contrast agents due to a large longitudinal relaxivity of Gd(3+) (5.86 S(-1)·mM(-1) per Gd ion and 3.99 × 10(5) S(-1)·mM(-1) per nanocrystal).

Lanthanide-doped LiLuF(4) upconversion nanoprobes for the detection of disease biomarkers.

Lanthanide-doped upconversion nanoparticles (UCNPs) have shown great promise in bioapplications. Exploring new host materials to realize efficient upconversion luminescence (UCL) output is a goal of general concern. Herein, we develop a unique strategy for the synthesis of novel LiLuF4 :Ln(3+) core/shell UCNPs with typically high absolute upconversion quantum yields of 5.0 % and 7.6 % for Er(3+) and Tm(3+) , respectively. Based on our customized UCL biodetection system, we demonstrate for the first time the application of LiLuF4 :Ln(3+) core/shell UCNPs as sensitive UCL bioprobes for the detection of an important disease marker β subunit of human chorionic gonadotropin (β-hCG) with a detection limit of 3.8 ng mL(-1) , which is comparable to the β-hCG level in the serum of normal humans. Furthermore, we use these UCNPs in proof-of-concept computed tomography imaging and UCL imaging of cancer cells, thus revealing the great potential of LiLuF4 :Ln(3+) UCNPs as efficient nano-bioprobes in disease diagnosis.

The effect of surface coating on energy migration-mediated upconversion.

Lanthanide-doped upconversion nanoparticles have been the focus of a growing body of investigation because of their promising applications ranging from data storage to biological imaging and drug delivery. Here we present the rational design, synthesis, and characterization of a new class of core-shell upconversion nanoparticles displaying unprecedented optical properties. Specifically, we show that the epitaxial growth of an optically inert NaYF(4) layer around a lanthanide-doped NaGdF(4)@NaGdF(4) core-shell nanoparticle effectively prevents surface quenching of excitation energy. At room temperature, the energy migrates over Gd sublattices and is adequately trapped by the activator ions embedded in host lattices. Importantly, the NaYF(4) shell-coating strategy gives access to tunable upconversion emissions from a variety of activators (Dy(3+), Sm(3+), Tb(3+), and Eu(3+)) doped at very low concentrations (down to 1 mol %). Our mechanistic investigations make possible, for the first time, the realization of efficient emissions from Tb(3+) and Eu(3+) activators that are doped homogeneously with Yb(3+)/Tm(3+) ions. The advances on these luminescent nanomaterials offer exciting opportunities for important biological and energy applications.

Amine-Functionalized Lanthanide-Doped Zirconia Nanoparticles: Optical Spectroscopy, Time-Resolved Fluorescence Resonance Energy Transfer Biodetection, and Targeted Imaging

Ultrasmall inorganic oxide nanoparticles doped with trivalent lanthanide ions (Ln(3+)), a new and huge family of luminescent bioprobes, remain nearly untouched. Currently it is a challenge to synthesize biocompatible ultrasmall oxide bioprobes. Herein, we report a new inorganic oxide bioprobe based on sub-5 nm amine-functionalized tetragonal ZrO(2)-Ln(3+) nanoparticles synthesized via a facile solvothermal method and ligand exchange. By utilizing the long-lived luminescence of Ln(3+), we demonstrate its application as a sensitive time-resolved fluorescence resonance energy transfer (FRET) bioprobe to detect avidin with a record-low detection limit of 3.0 nM. The oxide nanoparticles also exhibit specific recognition of cancer cells overexpressed with urokinase plasminogen activator receptor (uPAR, an important marker of tumor biology and metastasis) and thus may have great potentials in targeted bioimaging.

Sub-10 nm Lanthanide-Doped CaF2 Nanoprobes for Time-Resolved Luminescent Biodetection†

Lanthanide-doped luminescent nanoparticles (NPs) haveevoked considerable interest due to their superior features,such as sharp f–f emission peaks, a long photoluminescence(PL) lifetime, low toxicity, and high resistance to photo-bleaching, which make them extremely suitable for use asalternatives to organic fluorescent dyes or quantum dots forvarious bioapplications.

Energy levels, fluorescence lifetime and Judd–Ofelt parameters of Eu3+ in Gd2O3 nanocrystals

Crystal-field (CF) levels below 36 000 cm(-1) of Eu3+ at the C-2 site of Gd2O3 nanorods are experimentally determined from the excitation and emission spectra at 10 K. The levels are analysed in terms of 20 freely varied free-ion and CF parameters, and energy-level fit yields a final standard deviation of 12.9 cm(-1), showing very good agreement between the observed and the calculated values. The Judd - Ofelt (JO) intensity parameters Omega(2,4,6) are determined to be 12.39, 2.02 and 0.19 ( in 10(-20) cm(2)) which takes J-mixing into account. For the first time the absolute value of the Omega(6) parameter is reliably determined. The calculated radiative transition rates and branching ratios for the transitions from D-5(0) agree well with the experiments. The size dependence of the JO intensity parameters of Eu3+ in RE2O3 (RE = Y, Gd, Lu) nanocrystals is clarified. The fluorescence lifetime of D-5(0) of Eu3+ in Gd2O3 nanorods is observed to be significantly affected by the surrounding media, giving rise to a filling factor of 0.58 for the nanoparticles.

Lanthanide-doped upconversion nanoparticles electrostatically coupled with photosensitizers for near-infrared-triggered photodynamic therapy

Lanthanide-doped upconversion nanoparticles (UCNPs) have recently shown great promise in photodynamic therapy (PDT). Herein, we report a facile strategy to fabricate an efficient NIR-triggered PDT system based on LiYF4:Yb/Er UCNPs coupled with a photosensitizer of a β-carboxyphthalocyanine zinc (ZnPc-COOH) molecule via direct electrostatic interaction. Due to the close proximity between UCNPs and ZnPc-COOH, we achieved a high energy transfer efficiency of 96.3% from UCNPs to ZnPc-COOH, which facilitates a large production of cytotoxic singlet oxygen and thus an enhanced PDT efficacy. Furthermore, we demonstrate the high efficacy of such a NIR-triggered PDT agent for the inhibition of tumor growth both in vitro and in vivo, thereby revealing the great potential of the UCNP-based PDT systems as noninvasive NIR-triggered PDT agents for deep cancer therapy.

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.