Constructing Interfacial Energy Transfer for Photon Up- and Down-Conversion from Lanthanides in a Core-Shell Nanostructure

Nanoemulsion fluorescent inks for anti-counterfeiting encryption with dual-mode, full-color, and long-term stability

An oil-in-water nanoemulsion (O/W NE) is selected as the carrier to encapsulate hydrophobic dual-mode luminescent upconversion nanoparticles (UC NPs) and downconversion (DC) carbon quantum dots (CQDs) inside the oil droplets for forming water-based fluorescent inks. The NE inks conform well to the requirements of inkjet printing for anti-counterfeiting encryption applications.

Direct Identification of Surface Defects and Their Influence on the Optical Characteristics of Upconversion Nanoparticles

Core-shell structure is an obvious concept to suppress surface-related deactivations in lanthanide-doped upconversion nanoparticles (UCNPs). However, no direct observation of atomic-scale surface restoration, which can improve the upconversion photoluminescence, has been reported. Here, we use aberration-corrected high-angle annular dark field scanning transmission electron microscopy to study the surface condition of KLu₂F₇:Yb³⁺,Er³⁺ bare core UCNPs. Due to the very thin and uniform thickness of the UCNPs, we observe unambiguously that the recovery from surface defects enhances upconversion photoluminescence. Furthermore, the realization of dominant green lasing emission under pulsed laser excitation confirms the high crystallinity of the UCNPs.

808 nm excited energy migration upconversion nanoparticles driven by a Nd3+-Trinity system with color-tunability and superior luminescence properties

We have developed energy migration upconversion (EMU) nanoparticles (UCNPs) with optimal Nd³⁺-sensitization under excitation of an 808 nm laser to avoid over-heating effects caused by a 980 nm laser while maximizing the excitation efficiency. To realize efficient 808 nm sensitization, a "Nd³⁺-Trinity system" was implemented in the energy migration upconversion (EMU) cores (NaGdF₄:Yb,Tm@NaGdF₄:Yb,X, X = Eu/Tb), resulting in a core-multishell structure of EMU cores (accumulation layer@activation layer)@transition layer@harvest layer@activation layer. The spatially separated dopants and optimized Yb³⁺/Nd³⁺ content effectively prevented severe quenching events in the UCNPs and their Nd³⁺-sensitized EMU-based photoluminescence mechanism was studied under 808 nm excitation. These Nd³⁺-Trinity EMU system UCNPs presented enhanced upconversion luminescence and prolonged lifetime compared to the 980 nm excited UCNPs of the EMU system. It is proposed that 975 nm and 1056 nm NIR photons induced from the Nd³⁺ → Yb³⁺ energy transfer facilitate the Tm³⁺ accumulation process due to the matched energy gaps, which contributes to the extended lifetimes. More importantly, the synthesized UCNPs had a small average size of sub-15 nm and they not only exhibited color-tunability via Eu³⁺/Tb³⁺ activators, but also released a larger portion of Tm³⁺ red emission at 647 nm and had better penetration ability in water under 808 nm excitation, which are favorable for bioimaging applications.

Near-Infrared Triggered Decomposition of Nanocapsules with High Tumor Accumulation and Stimuli Responsive Fast Elimination

A near-infrared (NIR) induced decomposable polymer nanocapsule is demonstrated. The nanocapsules are fabricated based on layer-by-layer co-assembly of azobenzene functionalized polymers and up/downconversion nanoparticles (U/DCNPs). When the nanocapsules are exposed to 980 nm light, ultraviolet/visible photons emitted by the U/DCNPs can trigger the photoisomerization of azobenzene groups in the framework. The nanocapsules could decompose from large-sized nanocapsule to small U/DCNPs. Owing to their optimized original size (ca. 180 nm), the nanocapsules can effectively avoid biological barriers, provide a long blood circulation (ca. 5 h, half-life time) and achieve four-fold tumor accumulation. It can fast eliminate from tumor within one hour and release the loaded drugs for chemotherapy after NIR-induced dissociation from initial 180 nm capsules to small 20 nm U/DCNPs.

Manipulating energy transfer in lanthanide-doped single nanoparticles for highly enhanced upconverting luminescence

Energy transfer (ET) is of fundamental importance in tuning the optical performance of lanthanide-doped upconversion nanoparticles (UCNPs). However, the fine control and manipulation of the ETs particularly for deleterious cross-relaxation type ETs (CR-ETs) in lanthanide-doped UCNPs remains a formidable challenge to date. Herein, we demonstrate a rational design strategy to manipulate the deleterious CR-ETs in lanthanide-doped UCNPs, by fine-tuning the distances at an extremely large length scale (>20 nm) among multiple lanthanide dopants that are simultaneously embedded into one single nanoparticle with specially designed multilayer nanostructures. The successful inhibition of the CR-ETs leads to a significantly enhanced upconversion luminescence signal with an intensity ∼70 times higher than that of co-doped conventional UCNPs. This finding paves a new way for the better control of the ETs in lanthanide-doped nanoparticles, and offers the possibility of constructing a series of promising single-nanocrystal-based anti-counterfeiting barcodes with well-identified UC emission color and lifetime outputs.

Versatile design and synthesis of nano-barcodes

This review provides a critical discussion on the versatile designing and usage of nano-barcodes for various existing and emerging applications.