Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Rare-Earth Doping in Nanostructured Inorganic Materials.

Ultra-sensitive optical nano-thermometer LaPO4: Yb3+/Nd3+ based on thermo-enhanced NIR-to-NIR emissions

Optical temperature sensing of up-conversion luminescent materials: Fundamentals and progress

Rational Design of Ratiometric Luminescence Thermometry Based on Thermally Coupled Levels for Bioapplications

A Theoretical Framework for Ratiometric Single Ion Luminescent Thermometers—Thermodynamic and Kinetic Guidelines for Optimized Performance

Nd3+-doped near-infrared (NIR) luminescent nanocrystals (NCs) have shown great promise in various bioapplications. A fundamental understanding of the electronic structures of Nd3+ in NCs is of vital importance for discovering novel Nd3+-activated luminescent nanoprobes and exploring their new applications. Herein, the electronic structures of Nd3+ in LiLuF4 NCs are unraveled by means of low-temperature and high-resolution optical spectroscopy. The photoactive site symmetry of Nd3+ in LiLuF4 NCs and its crystal-field (CF) transition lines in the NIR region of interest are identified. By taking advantage of the well-resolved and sharp CF transition lines of Nd3+, the application of LiLuF4:Nd3+ NCs as sensitive NIR-to-NIR luminescent nanoprobes for ratiometric detection of cryogenic temperature with a linear range of 77-275 K is demonstrated. These findings reveal the great potential of LiLuF4:Nd3+ NCs in temperature sensing and also lay a foundation for future design of efficient Nd3+-based luminescent nanoprobes.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201802282

Unraveling the Electronic Structures of Neodymium in LiLuF4 Nanocrystals for Ratiometric Temperature Sensing.

Lanthanide (Ln3+ )-doped luminescent nanoparticles (NPs) with emission in the second near-infrared (NIR-II) biological window have shown great promise but their applications are currently limited by the low absorption efficiency of Ln3+ owing to the parity-forbidden 4f→4f electronic transition. Herein, we developed a strategy for the controlled synthesis of a new class of NIR-II luminescent nanoprobes based on Ce3+ /Er3+ and Ce3+ /Nd3+ co-doped CaS NPs, which can be effectively excited by using a low-cost blue light-emitting diode chip. Through sensitization by the allowed 4f→5d transition of Ce3+ , intense NIR-II luminescence from Er3+ and Nd3+ with quantum yields of 9.3 % and 7.7 % was achieved, respectively. By coating them with a layer of amphiphilic phospholipids, these NPs exhibit excellent stability in water and can be exploited as sensitive NIR-II luminescent nanoprobes for the accurate detection of an important disease biomarker, xanthine, with a detection limit of 32.0 nm.

A New Class of Blue-LED-Excitable NIR-II Luminescent Nanoprobes Based on Lanthanide-Doped CaS Nanoparticles

Near-infrared (NIR) photostimulated luminescence (PSL) nanocrystals (NCs) have recently evoked considerable interest in the field of biomedicine, but are currently limited by the controlled synthesis of efficient PSL NCs. Herein, we report for the first time the controlled synthesis of CaS:Eu2+,Sm3+ NIR PSL NCs through a high-temperature co-precipitation method. The role of Sm3+ co-doping and the effect of thermal annealing on the optical properties of the NCs as well as the charging and discharging processes, the trap depth distribution, and the underlying PSL mechanism are comprehensively surveyed by means of photoluminescence, persistent luminescence, thermoluminescence, and PSL spectroscopies. The as-prepared NCs exhibit intense PSL of Eu2+ at 650 nm with a fast response to stimulation in a broad NIR region from 800 nm to 1600 nm, a duration time longer than 2 h, and an extremely low power density threshold down to 10 mW cm−2 at 980 nm. Furthermore, by taking advantage of the intense NIR PSL, we demonstrate the application of CaS:Eu2+,Sm3+ NCs as sensitive luminescent nanoprobes for biotin receptor-targeted cancer cell imaging. These results reveal the great promise of CaS:Eu2+,Sm3+ nanoprobes for autofluorescence-free bioimaging, and also lay the foundation for future design of efficient NIR PSL nanoprobes towards versatile bioapplications.

/pdf/broadband-nir-photostimulated-luminescence-nanoprobes-based-37zz599ys2.pdf

Broadband NIR photostimulated luminescence nanoprobes based on CaS:Eu2+,Sm3+ nanocrystals

Highly efficient Sb3+ emitters in 0D cesium indium chloride nanocrystals with switchable photoluminescence through water-triggered structural transformation

All-inorganic lead-free perovskite-derivative metal halides have shown great promise in optoelectronics, however, it remains challenging to realize efficient near-infrared (NIR) luminescence in these materials. Herein, we report a novel strategy based on Te4+/Ln3+ (Ln = Er, Nd, and Yb) co-doping to achieve efficient NIR luminescence in vacancy-ordered double perovskite Cs2ZrCl6 phosphors, which are excitable by a low-cost near-ultraviolet light-emitting diode (LED) chip. Through sensitization by the spin-orbital allowed 1S0 → 3P1 transition of Te4+, intense and multi-wavelength NIR luminescence originating from the 4f → 4f transitions of Er3+, Nd3+, and Yb3+ was acquired, with a quantum yield of 6.1% for the Er3+ emission. These findings provide a general approach to achieve efficient NIR emission in lead-free metal halides through ns2-metal and lanthanide ion co-doping, thereby opening up a new avenue for exploring NIR-emitting perovskite derivatives towards versatile applications such as NIR-LEDs and bioimaging.

Meiran Zhang

Papers

Unraveling the Electronic Structures of Neodymium in LiLuF4 Nanocrystals for Ratiometric Temperature Sensing.

A New Class of Blue-LED-Excitable NIR-II Luminescent Nanoprobes Based on Lanthanide-Doped CaS Nanoparticles

Broadband NIR photostimulated luminescence nanoprobes based on CaS:Eu2+,Sm3+ nanocrystals

Highly efficient Sb3+ emitters in 0D cesium indium chloride nanocrystals with switchable photoluminescence through water-triggered structural transformation

Efficient Near-Infrared Luminescence in Lanthanide-Doped Vacancy-Ordered Double Perovskite Cs2ZrCl6 Phosphors via Te4+ Sensitization.