Expanding the toolbox of photon upconversion for emerging frontier applications

Abstract

This review summarizes the recent progress on lanthanide-based upconversion materials, focusing on the emerging approaches to the smart control of upconversion, and their frontier applications.

Comparison of Quantum Yield of Upconversion Nanocrystals Determined by Absolute and Relative Methods

“…As NCs are the most intensively investigated class of UC materials, [ 33,34 ] a NC‐based UC system is chosen for a comparison of the absolute method and the relative method; the latter using the reference SrF 2 :1%Yb 3+ ,1%Er 3+ single crystal. The NC sample, with a α‐NaYF 4 :18%Yb 3+ ,2%Er 3+ @CaF 2 core@shell structure, is chosen for a number of reasons.…”

Upconversion Luminescence via Anion Exchange in Perovskite Quantum Dots for Anticounterfeiting Inkjet Printing

“…In the past decade, cesium lead halide (CPX 3 , X = Cl, Br, and I) perovskite quantum dots (PeQDs) have attracted a lot of attention due to the outstanding optical properties such as the large absorption coefficient, high quantum yields, emission peaks with narrow full width at half maximum (FWHM), and so on. , In addition, the ease of tuning the band gap via modulating the halide composition, thus shifting the single-peak emissive profiles from deep blue to red continuously, endows the materials with huge potential in wide applications such as displays, photovoltaics, optoelectronics, and so on. − Meanwhile, lanthanide-doped upconversion nanoparticles (UCNPs), giving off anti-Stokes upconversion luminescence (UCL) under 980 nm NIR laser excitation, have demonstrated unparallel virtues against Stokes luminescence in various fields. − However, unlike PeQDs, UCNPs critically rely on the dopants’ energy levels, with fixed UCL emissive peaks at certain wavelengths. Consequently, the UCL manipulation strategy has always been intensively focused over the decades.…”

“… 3 − 8 Meanwhile, lanthanide-doped upconversion nanoparticles (UCNPs), giving off anti-Stokes upconversion luminescence (UCL) under 980 nm NIR laser excitation, have demonstrated unparallel virtues against Stokes luminescence in various fields. 9 − 13 However, unlike PeQDs, UCNPs critically rely on the dopants’ energy levels, with fixed UCL emissive peaks at certain wavelengths. Consequently, the UCL manipulation strategy has always been intensively focused over the decades.…”

Multichannel Control of PersL/Upconversion/Down-Shifting Luminescence in a Single Core–Shell Nanoparticle for Information Encryption

“…Persistent luminescence (PersL) is an interesting phenomenon, which is able to release the energy in form of light emission with a long time duration (from a few seconds to days), showing great promise in applications of temperature dosimeters, optical storage, and information anticounterfeiting. − Such a slow luminescence process results from the controllable release of irradiation energy trapped in the matrix. − Typical PersL materials include SrAl 2 O 4 :Eu 2+ /Dy 3+ , Ca 2 Al 2 SiO 7 :Pr 3+ , Zn 3 Ga 2 Ge 2 O 10 :Cr 3+ , and LaMgGa 11 O 19 :Pr 3+ with emissions ranging from ultraviolet (UV) to visible and near-infrared regions. − Compared to traditional luminescent materials, a unique feature of PersL materials is that they can be precharged before being deployed in biological systems. This can avoid autofluorescence or background scattering induced by the excitation light, resulting in clearer imaging of biological tissues together with long-term usage. , In addition, the design of core–shell nanoparticles facilitates their functionalization, such as multiwavelength excitable luminescence. , Although this can be obtained in the powder materials based on the codoping scheme, the complex cross-relaxation processes would cause serious energy loss with a resultant significant decrease in luminescence intensity. − Using the epitaxial growth method, a reasonable core–shell structure design can integrate more excitation–emission modes with multicolor output on a single nanoparticle level. − However, the current excitation light sources used for PersL are usually high-energy X-rays, and the materials are mostly limited to bulk or powder phosphors, which cannot be applied to biological applications. The development of nanometer-sized PersL materials with much low energy photon (e.g., UV light) excitations is urgently needed.…”

“…13,14 In addition, the design of core−shell nanoparticles facilitates their functionalization, such as multiwavelength excitable luminescence. 15,16 Although this can be obtained in the powder materials based on the codoping scheme, the complex cross-relaxation processes would cause serious energy loss with a resultant significant decrease in luminescence intensity. 17−19 Using the epitaxial growth method, a reasonable core−shell structure design can integrate more excitation− emission modes with multicolor output on a single nanoparticle level.…”