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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 ]

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.

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.

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.

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.

Visible-to-infrared quantum cutting by phonon-assisted energy transfer in YPO4:Tm3+, Yb3+ phosphors

Quantum cutting (QC) of one visible photon into two infrared ones has been reported for the lanthanide ion couple (Tm(3+), Yb(3+)) in a variety of host lattices. The mechanism responsible for QC was assumed to be a cooperative energy transfer (ET) process from Tm(3+) to two Yb(3+) ions, however, no solid evidence was presented. Herein we report visible-to-infrared QC for (Tm(3+), Yb(3+)) in YPO4 phosphors. The ET process from the excited (1)G4 level of Tm(3+) to Yb(3+) was investigated in detail by means of optical spectroscopy. By monitoring the steady-state photoluminescence (PL) and PL decay of the intermediate (3)F4 level of Tm(3+) as a function of the Yb(3+) concentration, we demonstrated the QC of one incident blue photon into one near-infrared emitting photon at 1004 nm from Yb(3+) and simultaneously into one mid-infrared emitting photon at 1791 nm from Tm(3+), rather than two emitting photons from Yb(3+). It was revealed that such visible-to-infrared QC was induced by phonon-assisted ET instead of cooperative ET as previously reported. This kind of QC phosphors may have potential as solar spectral converters to enhance the external quantum efficiency in multi-junction solar cells based on narrow band-gap semiconductors such as Ge, PbS or In1-xGaxN.

Single-composition white-emitting NaSrBO3:Ce3+,Sm3+,Tb3+ phosphors for NUV light-emitting diodes

Single-composition (or single-phase) phosphors have been proposed as a new strategy to overcome the concerns of emission reabsorption and different degradation rates of the three primary phosphors for light-emitting diode (LED) applications. A series of Ce3+, Sm3+ and Tb3+ co-doped NaSrBO3 phosphors were synthesized via a high temperature solid-state reaction. Upon near ultraviolet (NUV) excitation, tunable emission from violet to white in the visible region was realized in NaSrBO3:Ce3+,Sm3+,Tb3+ phosphors by controlling the dopant concentrations. Particularly, highly efficient white-light emission with a quantum yield as high as 48.2% was achieved. The energy transfer mechanism between Ce3+ and Sm3+ ions in NaSrBO3 was found to be predominantly of dipole–dipole nature. Moreover, the thermal quenching effect on the photoluminescence of NaSrBO3:Ce3+,Sm3+,Tb3+ was comprehensively surveyed over the range of 300–600 K, showing a good thermal stability for LED applications. By integrating this single-composition white-emitting NaSrBO3:Ce3+,Sm3+,Tb3+ phosphor with a 360 nm NUV chip, we fabricated a high-performance white LED (WLED), which exhibited an excellent color rendering index Ra of 80.1 and a correlated color temperature of 6731 K with CIE coordinates of (0.311, 0.314). These findings demonstrate that the proposed single-composition white-emitting NaSrBO3:Ce3+,Sm3+,Tb3+ phosphors can serve as promising phosphors for NUV-excited WLEDs.

Lanthanide-doped NaScF4 nanoprobes: crystal structure, optical spectroscopy and biodetection

Trivalent lanthanide ions (Ln(3+))-doped inorganic nanoparticles (NPs) as potential luminescent bioprobes have been attracting tremendous interest because of their unique upconversion (UC) and downconversion (DC) luminescence properties. NaScF4, as an important host material, has been rarely reported and its crystal structure remains unclear. Herein, based on the single crystal X-ray diffraction, the space group of NaScF4 crystals was determined to be P31 containing multiple sites of Sc(3+) with crystallographic site symmetry of C1, which was verified by high-resolution photoluminescence spectroscopy of Eu(3+) at low temperature (10 K). Furthermore, monodisperse and size-controllable NaScF4:Ln(3+) NPs were synthesized via a facile thermal decomposition method. The biotinylated NaScF4:Er(3+)/Yb(3+) NPs were demonstrated for their applications as a heterogeneous UC luminescence bioprobe to detect avidin with a detection limit of 180 pM. After bioconjugation with amino-terminal fragment (ATF) of urokinase plasminogen activator (uPA), NaScF4:Ln(3+) NPs also exhibited specific recognition of cancer cells overexpressed with uPA receptor (uPAR, an important marker of tumor biology and metastasis), showing great potentials in tumor-targeted bioimaging.