Dynamic modulation of multicolor upconversion luminescence of Er3+ via excitation pulse width.

Lanthanide-doped upconversion (UC) luminescent materials display multicolor emissions, making them ideal for a variety of applications, such as multi-channel biological imaging, fluorescence encryption, anti-counterfeiting, and 3D display. Manipulating the UC emissions of the luminescent materials with a fixed composition is crucial for their applications. Herein, we propose a facile strategy to achieve pulse-width-dependent multicolor UC emissions in NaYF4:Yb/Er/Tm nanocrystals. Upon excitation with a 980 nm continuous-wave laser diode, Er3+ ions in NaYF4:20%Yb,15%Er,1%Tm nanocrystals exhibited UC emissions with a red-to-green (R/G) ratio of 11.3. Nevertheless, by employing a 980 nm pulse laser with pulse widths from 0.1 to 10 ms, the UC R/G ratio can be easily adjusted from 0.9 to 11.3, resulting in continuous and remarkable color transformation from green, yellow, orange, to red. By virtue of the dynamic luminescence color variation of these NaYF4:20%Yb,15%Er,1%Tm nanocrystals, we demonstrated their potential applications in the areas of anti-counterfeiting and information encryption. These findings provide deep insights into the excited-state dynamics and energy transfer of Er3+ in NaYF4:Yb/Er/Tm nanocrystals upon 980 nm pulse excitation, which may pave the way for designing multicolor UC materials toward versatile applications.

Ultrasensitive Urinary Diagnosis of Organ Injuries Using Time-Resolved Luminescent Lanthanide Nano-bioprobes.

Urinary sensing of synthetic biomarkers that are released into urine after specific activation in an in vivo disease environment is an emerging diagnosis strategy to overcome the insensitivity of a previous biomarker assay. However, it remains a great challenge to achieve sensitive and a specific urinary photoluminescence (PL) diagnosis. Herein, we report a novel urinary time-resolved PL (TRPL) diagnosis strategy by exploiting europium complexes of diethylenetriaminepentaacetic acid (Eu-DTPA) as synthetic biomarkers and designing the activatable nanoprobes. Notably, TRPL of Eu-DTPA in the enhancer can eliminate the urinary background PL for ultrasensitive detection. We achieved sensitive urinary TRPL diagnosis of mice kidney and liver injuries by using simple Eu-DTPA and Eu-DTPA-integrated nanoprobes, respectively, which cannot be realized by traditional blood assays. This work demonstrates the exploration of lanthanide nanoprobes for in vivo disease-activated urinary TRPL diagnosis for the first time, which might advance the noninvasive diagnosis of diverse diseases via tailorable nanoprobe designs.

Tumor-Microenvironment-Responsive Biodegradable Nanoagents Based on Lanthanide Nucleotide Self-Assemblies toward Precise Cancer Therapy.

Stimuli-responsive nanoagents, which simultaneously satisfy normal tissue clearance and tumor-specific responsive treatment, are highly attractive for precise cancer theranostics. Herein, we develop a unique template-induced self-assembly strategy for the exquisitely controlled synthesis of self-assembled lanthanide (Ln3+ ) nucleotide nanoparticles (LNNPs) with amorphous structure and tunable size from sub-5 nm to 105 nm. By virtue of the low-temperature (10 K) and high-resolution spectroscopy, the local site symmetry of Ln3+ in LNNPs is unraveled for the first time. The proposed LNNPs are further demonstrated to possess the ability for highly efficient loading and tumor-microenvironment-responsive release of doxorubicin. Particularly, sub-5 nm LNNPs not only exhibit excellent biocompatibility and predominant renal-clearance performance, but also enable efficient tumor retention. These findings reveal the great potential of LNNPs as a new generation of therapeutic platform to overcome the dilemma between efficient therapy and long-term toxicity of nanoagents for future clinical applications.

Boosting Near-Infrared Luminescence of Lanthanide in Cs2 AgBiCl6 Double Perovskites via Breakdown of the Local Site Symmetry.

Currently, lanthanide (Ln3+ )-doped near-infrared (NIR)-emitting double perovskites (DPs) suffer from low photoluminescence quantum yield (PLQY). Herein, we develop a new class of NIR-emitting DPs based on Ln3+ -doped Cs2 (Na/Ag)BiCl6 . Benefiting from the Na+ -induced breakdown of local site symmetry in the Cs2 AgBiCl6 DPs, effective NIR emissions of Ln3+ are realized through Bi3+ sensitization. Specifically, 7.3-fold and 362.9-fold enhanced NIR emissions of Yb3+ and Er3+ are achieved in Cs2 Ag0.2 Na0.8 BiCl6 DPs relative to those in Na-free Cs2 AgBiCl6 counterparts, respectively. The optimal absolute NIR PLQYs for Yb3+ and Er3+ in Cs2 Ag0.2 Na0.8 BiCl6 DPs are determined to be 19.0 % and 4.3 %, respectively. Raman spectroscopy and first-principles density functional theory calculations verify the sublattice distortion in Cs2 (Na/Ag)BiCl6 DPs via Na+ doping. These findings provide fundamental insights into the design of efficient NIR-emitting Ln3+ -doped DPs for versatile optoelectronic applications.

Enhancing Dye-Triplet-Sensitized Upconversion Emission Through the Heavy-Atom Effect in CsLu2 F7 :Yb/Er Nanoprobes.

Lanthanide (Ln3+ )-doped upconversion (UC) nanoprobes, which have drawn extensive attention for various bioapplications, usually suffer from small absorption cross-sections and weak luminescence intensity of Ln3+ ions. Herein, we report the controlled synthesis of a new class of Ln3+ -doped UC nanoprobes based on CsLu2 F7 :Yb/Er nanocrystals (NCs), which can effectively increase the intersystem crossing (ISC) efficiency from singlet excited state to triplet excited state of IR808 up to 99.3 % through the heavy atom effect. By virtue of the efficient triplet sensitization of IR808, the optimal UC luminescence (UCL) intensity of IR808-modified CsLu2 F7 :Yb/Er NCs is enhanced by 1309 times upon excitation at 808 nm. Benefiting from the intense dye-triplet-sensitized UCL, the nanoprobes are demonstrated for sensitive assay of extracellular and intracellular hypochlorite with an 808-nm/980-nm dual excited ratiometric strategy.

Colloidal Alloyed Quantum Dots with Enhanced Photoluminescence Quantum Yield in the NIR-II Window.

Semiconductor quantum dots (QDs) with photoluminescence (PL) emission at 900-1700 nm (denoted as the second near-infrared window, NIR-II) exhibit much-depressed photon absorption and scattering, which has stimulated extensive researches in biomedical imaging and NIR devices. However, it is very challenging to develop NIR-II QDs with a high photoluminescence quantum yield (PLQY) and excellent biocompatibility. Herein, we designed and synthesized an alloyed silver gold selenide (AgAuSe) QD with a bright emission from 820 to 1170 nm and achieved a record absolute PLQY of 65.3% at 978 nm emission among NIR-II QDs without a toxic element and a long lifetime of 4.58 µs. It is proved that the high PLQY and long lifetime are mainly attributed to the prevented nonradiative transition of excitons, probably resulted from suppressing cation vacancies and crystal defects from the high mobility of Ag ions by alloying Au atoms. These high-PLQY QDs with nontoxic heavy metal exhibit great application potential in bioimaging, light emitting diodes (LEDs), and photovoltaic devices.

Engineering the Bandgap and Surface Structure of CsPbCl3 Nanocrystals to Achieve Efficient Ultraviolet Luminescence.

Herein, we report the design of novel ultraviolet luminescent CsPbCl3 nanocrystals (NCs) with the emission peak at 381 nm through doping of cadmium ions. Subsequently, a surface passivation strategy with CdCl2 is adopted to improve their photoluminescence quantum yield (PLQY) with the maximum value of 60.5 %, which is 67 times higher than that of the pristine counterparts. The PLQY of the surface passivated NCs remains over 50 % after one week while the pristine NCs show negligible emission. By virtue of density functional theory calculations, we reveal that the higher PLQY and better stability after surface passivation may result from the significant elimination of surface chloride vacancy (VCl ) defects. These findings provide fundamental insights into the optical manipulation of metal ion-doped CsPbCl3 NCs.

Full-Spectrum Persistent Luminescence Tuning Using All-Inorganic Perovskite Quantum Dots.

Applications of persistent luminescence phosphors as night or dark-light vision materials in many technological fields have fueled up a growing demand for rational control over the emission profiles of the phosphors. This, however, remains a daunting challenge. Now a unique strategy is reported to fine-tune the persistent luminescence by using all-inorganic CsPbX3 (X=Cl, Br, and I) perovskite quantum dots (PeQDs) as efficient light-conversion materials. Full-spectrum persistent luminescence with wavelengths covering the entire visible spectral region is achieved through tailoring of the PeQD band gap, in parallel with narrow bandwidth of PeQDs and highly synchronized afterglow decay owing to the single energy storage source. These findings break through the limitations of traditional afterglow phosphors, thereby opening up opportunities for persistent luminescence materials for applications such as a white-emitting persistent light source and dark-light multicolor displays.

Graphene-Oxide-Modified Lanthanide Nanoprobes for Tumor-Targeted Visible/NIR-II Luminescence Imaging.

The synthesis of hydrophilic lanthanide-doped nanocrystals (Ln3+ -NCs) with molecular recognition ability for bioimaging currently remains a challenge. Herein, we present an effective strategy to circumvent this bottleneck by encapsulating Ln3+ -NCs in graphene oxide (NCs@GO). Monodisperse NCs@GO was prepared by optimizing GO size and core-shell structure of NaYF4 :Yb,Er@NaYF4 , thus combining the intense visible/near-infrared II (NIR-II) luminescence of NCs and the unique surface properties and biomedical functions of GO. Such nanostructures not only feature broad solvent dispersibility, efficient cell uptake, and excellent biocompatibility but also enable further modifications with various agents such as DNA, proteins, or nanoparticles without tedious procedures. Moreover, we demonstrate in proof-of-concept experiments that NCs@GO can realize simultaneous intracellular tracking and microRNA-21 visualization, as well as highly sensitive in vivo tumor-targeted NIR-II imaging at 1525 nm.

Near-Infrared Light-Mediated Photodynamic Therapy Nanoplatform by the Electrostatic Assembly of Upconversion Nanoparticles with Graphitic Carbon Nitride Quantum Dots.

Photodynamic therapy (PDT) is a promising antitumor treatment that is based on photosensitizers. This therapy kills cancer cells by generating reactive oxygen species (ROS) after irradiation with specific laser wavelengths. Being a potential photosensitizer, graphitic carbon nitride (g-C3N4) quantum dots (QDs) are noncytotoxic. Although the use of g-C3N4 QDs is challenged by the limited tissue penetration of UV light, g-C3N4 QDs display excellent ultraviolet (UV) light-triggered cytotoxicity. The g-C3N4 QDs were synthesized using a solid-phase hydrothermal method. The well-distributed hydrophilic g-C3N4 can be combined with NaYF4:Yb3+/Tm3+ upconversion nanoparticles via the positive ligand poly(l-lysine) to produce the final nanocomposite, NaYF4:Yb/Tm-PLL@g-C3N4. Upconversion nanoparticles can transfer IR light into UV light and promote g-C3N4 to release blue-to-green visible light to generate different images. Moreover, g-C3N4 is a promising photosensitizer in PDT because g-C3N4 can transfer oxygen into toxic ROS. The singlet oxygen formed by g-C3N4 displays great potential for use in the treatment of cancer.

Lanthanide-doped upconversion nano-bioprobes: electronic structures, optical properties, and biodetection.

Lanthanide-doped upconversion nanoparticles (UCNPs) have attracted considerable interest due to their superior physicochemical features, such as large anti-Stokes shifts, low autofluorescence background, low toxicity and high penetration depth, which make them extremely suitable for use as alternatives to conventional downshifting luminescence bioprobes like organic dyes and quantum dots for various biological applications. A fundamental understanding of the photophysics of lanthanide-doped UCNPs is of vital importance for discovering novel optical properties and exploring their new applications. In this review, we focus on the most recent advances in the development of lanthanide-doped UCNPs as potential luminescent nano-bioprobes by means of our customized lanthanide photophysics measurement platforms specially designed for upconversion luminescence, which covers from their fundamental photophysics to bioapplications, including electronic structures (energy levels and local site symmetry of emitters), excited-state dynamics, optical property designing, and their promising applications for in vitro biodetection of tumor markers. Some future prospects and efforts towards this rapidly growing field are also envisioned.

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 ß-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 ß-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 luminescent nanoprobes: controlled synthesis, optical spectroscopy, and bioapplications.

Lanthanide-doped inorganic nanoparticles possess superior physicochemical features such as long-lived luminescence, large antenna-generated Stokes or anti-Stokes shifts, narrow emission bands, high resistance to photobleaching and low toxicity, and thus are regarded as a new generation of luminescent bioprobes as compared to conventional molecular probes like organic dyes and lanthanide chelates. These functional nanoparticles, although most of their bulk counterparts were well studied previously, have attracted renewed interest for their biomedical applications in areas as diverse as biodetection, bioimaging, and disease diagnosis and therapeutics. In this review, we provide a comprehensive survey of the latest advances made in developing lanthanide-doped inorganic nanoparticles as potential luminescent bioprobes, which covers areas from their fundamental chemical and physical features to bioapplications including controlled synthesis methodology, surface modification chemistry, optical spectroscopy, and their promising applications in diverse fields, with an emphasis on heterogeneous and homogeneous in vitro biodetection of tumor markers and multimodal bioimaging of various tumor tissues. Some future prospects and challenges in this rapidly growing field are also summarized.

Dissolution-enhanced luminescent bioassay based on inorganic lanthanide nanoparticles.

Conventional dissociation-enhanced lanthanide fluoroimmunoassays (DELFIA) using molecular probes suffer from a low labeling ratio of lanthanide ions (Ln(3+) ) per biomolecule. Herein, we develop a unique bioassay based on the dissolution-enhanced luminescence of inorganic lanthanide nanoparticles (NPs). As a result of the highly concentrated Ln(3+)  ions in a single Ln(3+)  NP, an extremely high Ln(3+)  labeling ratio can be achieved, which amplifies significantly the luminescence signal and thus improves the detection sensitivity compared to DELFIA. Utilizing sub-10 nm NaEuF4  NPs as dissolution-enhanced luminescent nanoprobes, we demonstrate the successful in vitro detection of carcinoembryonic antigen (CEA, an important tumor marker) in human serum samples with a record-low detection limit of 0.1 pg mL(-1) (0.5 fM). This value is an improvement of approximately 3 orders of magnitude relative to that of DELFIA. The dissolution-enhanced luminescent bioassay shows great promise in versatile bioapplications, such as ultrasensitive and multiplexed in vitro detection of disease markers in clinical diagnosis.

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 ß subunit of human chorionic gonadotropin (ß-hCG) with a detection limit of 3.8 ng mL(-1) , which is comparable to the ß-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.

Near-Infrared Nanophosphors Based on CuInSe2 Quantum Dots with Near-Unity Photoluminescence Quantum Yield for Micro-LEDs Applications.

Highly efficient near-infrared (NIR) luminescent nanomaterials are urgently required for portable mini or micro phosphors-converted light-emitting diodes (pc-LEDs). However, most existing NIR-emitting phosphors are generally restricted by their low photoluminescence (PL) quantum yield (QY) or large particle size. Herein, a kind of highly efficient NIR nanophosphors is developed based on copper indium selenide quantum dots (CISe QDs). The PL peak of these QDs can be exquisitely manipulated from 750 to 1150 nm by altering the stoichiometry of Cu/In and doping with Zn2+ . Their absolute PLQY can be significantly improved from 28.6% to 92.8% via coating a ZnSe shell. By combining the phosphors with a commercial blue chip, an NIR pc-LED is fabricated with remarkable photostability and a record-high radiant flux of 88.7 mW@350 mA among the Pb/Cd-free QDs-based NIR pc-LEDs. Particularly, such QDs-based nanophosphors acted as excellent luminescence converter for NIR micro-LEDs with microarray diameters below 5 µm, which significantly exceeds the resolutions of current commercial inkjet display pixels. The findings may open new avenues for the exploration of highly efficient NIR micro-LEDs in a variety of applications.

Optical/magnetic multimodal bioprobes based on lanthanide-doped inorganic nanocrystals.

Multimodal bioprobes, which integrate the advantages of different diagnostic modes into one single particle, can overcome the current limitations of sensitivity and resolution in medical assays and significantly improve the outcome of existing therapeutics. Lanthanide-doped inorganic multimodal bioprobes, which are emerging as a promising new class of optical/magnetic multimodal bioprobes, have been long sought-after and have recently attracted revived interest owing to their distinct optical and magnetic properties. In this concept article, we introduce the controlled synthesis of lanthanide-doped inorganic multimodal bioprobes, including core-shell structured and single-phase nanoparticles, and demonstrate different design strategies for achieving dual-modal functionalization of nanoprobes. In particular, we highlight the most recent advances in biodetection, bioimaging, targeted drug delivery, and therapy based on these nanoparticles.

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.

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).

Visible-to-infrared quantum cutting by phonon-assisted energy transfer in YPO4:Tm(3+), Yb(3+) 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.