Upconversion of Rare Earth Nanomaterials

Abstract

Rare earth nanomaterials, which feature long-lived intermediate energy levels and intraconfigurational 4f-4f transitions, are promising supporters for photon upconversion. Owing to their unique optical properties, rare earth upconversion nanomaterials have found applications in bioimaging, theranostics, photovoltaic devices, and photochemical reactions. Here, we review recent advances in the photon upconversion processes of these nanomaterials. We start by considering energy transfer models involved in the study of upconversion emissions, as well as well-established synthesis strategies to control the size and shape of rare earth upconversion nanomaterials. Progress in engineering energy transfer pathways, which play a dominant role in determining upconversion emission outputs, is then discussed. Lastly, representative optical applications of these materials are considered. The aim of this review is to provide inspiration for researchers to explore novel upconversion nanomaterials and extended optical applications.

Upconversion Modulation through Pulsed Laser Excitation for Anti-counterfeiting

“…2(d)). The overall emission intensity of NaYF 4 :Er/Tm nanocrystals was remarkably enhanced after NaYF 4 shell coating owing to elimination of quenchers on the surface of NaYF 4 :Er/Tm nanoparticles 10, 17 . Note that the enhancement factor for red emission is more prominent than that of the green emission, further elevating the red to green ratio.…”

Recent Advancements in Ln‐Ion‐Based Upconverting Nanomaterials and Their Biological Applications

“…Recently, tremendous attention has been paid on the synthesis and spectroscopic analysis of RE ion‐doped UCNPs with controlled shapes, sizes, and crystalline phases . A variety of synthetic methods have been identified that include coprecipitation, hydrothermal/solvothermal process, seed‐mediated heat‐up approach, decomposition of mixed trifluoroacetates, template method, sol–gel method, and Ostwald‐ripening epitaxial shell growth, which have been reviewed in many papers as well . These methods are the most widely used methods for the synthesis of UCNPs because they offer precise control over phases, sizes, and morphologies of UCNPs.…”

Recent Progress in Fluorescence Imaging of the Near‐Infrared II Window

“…In recent years, RE compounds have been applied to NIR‐II fluorescence imaging, and exceptional fluorescence tunability though the doping of different RE metal ions has been demonstrated . The fluorescence of RE compounds is attributed to resonant energy transfer between the sensitizer and RE activator dopant . Tuning the atomic makeup will be beneficial for the generation of sharp, narrow emission bands in the NIR‐II region .…”

“…[94][95][96] The fluorescenceo fR Ec ompounds is attributed to resonant energy transfer between the sensitizer and RE activator dopant. [97,98] Tuning the atomicm akeup will be beneficial for the generation of sharp, narrow emission bands in the NIR-II region. [94] Similart oo ther inorganic fluorophores, RE compounds exhibit minimal photobleaching under whole-body imaging conditions;t his indicates the possibility of monitoring disparate biological processes through multicolor imaging over extendedp eriodsoft ime.…”