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.
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.
The design of bright NIR‐II luminescent nanomaterials that enable efficient labelling of proteins without disturbing their physiological properties in vivo is challenging. We developed an efficient ...strategy to synthesize bright NIR‐II gold nanoclusters (Au NCs) protected by biocompatible cyclodextrin (CD). Leveraging the ultrasmall size of Au NCs (<2 nm) and strong macrocycle‐based host–guest chemistry, the as‐synthesized CD‐Au NCs can readily label proteins/antibodies. Moreover, the labelled proteins/antibodies enable highly efficient in vivo tracking during blood circulation, without disturbing their biodistribution and tumor targeting ability, thus leading to a sensitive tumor‐targeted imaging. CD‐Au NCs are stable in the harsh biological environment and show good biocompatibility and high renal clearance efficiency. Therefore, the NIR‐II biolabels developed in this study provide a promising platform to monitor the physiological behavior of biomolecules in living organisms.
Bright NIR‐II Au nanoclusters (NCs) were rationally synthesized by using biocompatible cyclodextrin (CD) as the ligands. The renal‐clearable CD‐Au NCs can readily label proteins/antibodies via strong macrocycle‐based host–guest chemistry and enable highly efficient in vivo tracking during blood circulation, without disturbing their biodistribution and tumor targeting ability, thus leading to a sensitive tumor‐targeted NIR‐II visualization.
Ag2S quantum dots (QDs) have attracted increasing attention due to their appealing optical properties in the near-infrared regime. However, a full understanding of the quantum confinement effect of ...Ag2S QDs has not been achieved so far. Herein, for the first time, the size-dependent excited state optical properties of Ag2S QDs are systematically investigated by photoluminescence (PL), PL excitation (PLE), and time-resolved PL spectroscopy. Experimentally, we determine the exciton Bohr radius of Ag2S QDs as 2.2 nm, which is highly consistent with theoretical results.
Impurity doping is an effective approach to tuning the optoelectronic performance of host materials by imparting extrinsic electronic channels. Herein, a family of lanthanide (Ln
) ions was ...successfully incorporated into a Bi:Cs
AgInCl
lead-free double-perovskite (DP) semiconductor, expanding the spectral range from visible (Vis) to near-infrared (NIR) and improving the photoluminescence quantum yield (PLQY). After multidoping with Nd, Yb, Er and Tm, Bi/Ln:Cs
AgInCl
yielded an ultrabroadband continuous emission spectrum with a full width at half-maximum of ~365 nm originating from intrinsic self-trapped exciton recombination and abundant 4f-4f transitions of the Ln
dopants. Steady-state and transient-state spectra were used to ascertain the energy transfer and emissive processes. To avoid adverse energy interactions between the various Ln
ions in a single DP host, a heterogeneous architecture was designed to spatially confine different Ln
dopants via a "DP-in-glass composite" (DiG) structure. This bottom-up strategy endowed the prepared Ln
-doped DIG with a high PLQY of 40% (nearly three times as high as that of the multidoped DP) and superior long-term stability. Finally, a compact Vis-NIR ultrabroadband (400~2000 nm) light source was easily fabricated by coupling the DiG with a commercial UV LED chip, and this light source has promising applications in nondestructive spectroscopic analyses and multifunctional lighting.
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:Ln3+ core/shell UCNPs with typically high absolute upconversion quantum yields of 5.0 % and 7.6 % for Er3+ and Tm3+, respectively. Based on our customized UCL biodetection system, we demonstrate for the first time the application of LiLuF4:Ln3+ 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:Ln3+ UCNPs as efficient nano‐bioprobes in disease diagnosis.
A small but sensitive biosensor: Successive injection of shell precursors enabled the synthesis of novel and highly emissive LiLuF4:Ln3+ core/shell upconversion nanoparticles that were effective as sensitive upconversion luminescent probes for the detection of β‐hCG (an important disease marker). The nanoprobes were also used successfully in proof‐of‐concept computed tomography and upconversion luminescence dual‐mode bioimaging.
Photon upconversion is promising for applications such as biological imaging, data storage or solar cells. Here, we have investigated upconversion processes in a broad range of gadolinium-based ...nanoparticles of varying composition. We show that by rational design of a core-shell structure with a set of lanthanide ions incorporated into separated layers at precisely defined concentrations, efficient upconversion emission can be realized through gadolinium sublattice-mediated energy migration for a wide range of lanthanide activators without long-lived intermediary energy states. Furthermore, the use of the core-shell structure allows the elimination of deleterious cross-relaxation. This effect enables fine-tuning of upconversion emission through trapping of the migrating energy by the activators. Indeed, the findings described here suggest a general approach to constructing a new class of luminescent materials with tunable upconversion emissions by controlled manipulation of energy transfer within a nanoscopic region.
Abstract
Rare earth (RE
3+
)-doped phosphors generally suffer from thermal quenching, in which their photoluminescence (PL) intensities decrease at high temperatures. Herein, we report a class of ...unique two-dimensional negative-thermal-expansion phosphor of Sc
2
(MoO
4
)
3
:Yb/Er. By virtue of the reduced distances between sensitizers and emitters as well as confined energy migration with increasing the temperature, a 45-fold enhancement of green upconversion (UC) luminescence and a 450-fold enhancement of near-infrared downshifting (DS) luminescence of Er
3+
are achieved upon raising the temperature from 298 to 773 K. The thermally boosted UC and DS luminescence mechanism is systematically investigated through in situ temperature-dependent Raman spectroscopy, synchrotron X-ray diffraction and PL dynamics. Moreover, the luminescence lifetime of
4
I
13/2
of Er
3+
in Sc
2
(MoO
4
)
3
:Yb/Er displays a strong temperature dependence, enabling luminescence thermometry with the highest relative sensitivity of 12.3%/K at 298 K and low temperature uncertainty of 0.11 K at 623 K. These findings may gain a vital insight into the design of negative-thermal-expansion RE
3+
-doped phosphors for versatile applications.
A strategy is proposed to fabricate dual‐mode luminescent NaGdF4 nanocrystals that are composed of NaGdF4:Yb3+,Tm3+ core and NaGdF4:Eu3+ shell. Intense downconversion via the sensitization of Gd3+ ...and upconversion luminescence of Eu3+ that is one order of magnitude higher than the triply‐doped core only counterparts have been achieved by employing the distinct core/shell nanostructures and double sensitizations of Yb3+ and Tm3+.
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.
A unique and versatile strategy is proposed to fine‐tune the persistent luminescence over the entire visible spectral region with narrow bandwidth and highly synchronized afterglow decay. It uses a CaAl2O4:Eu2+,Nd3+ (CAO) afterglow phosphor as the single energy storage source and all‐inorganic CsPbX3 (X=Cl, Br, and I) perovskite quantum dots (PeQDs) as efficient light conversion materials.
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