An Excitation Navigating Energy Migration of Lanthanide Ions in Upconversion Nanoparticles

Abstract

Upconversion nanoparticles (UCNPs) doped with lanthanide ions that possess ladder‐like energy levels can give out multiple emissions at specific ultra‐violet or visible wavelengths irrespective of excitation light. However, precisely controlling energy migration processes between different energy levels of the same lanthanide ion to generate switchable emissions remains elusive. Herein, a novel dumbbell‐shaped UCNP is reported with upconverted red emission switched to green emission when excitation wavelength changed from 980 to 808 nm. The sensitizer Yb ions are doped with activator Er ions and energy modulator Mn ions in NaYF4 core nanocrystal coated with an inner NaYF4:Yb shell to generate red emission after harvesting 980 nm excitation light, while an outer NaNdF4:Yb shell is coated to form a dumbbell shape to generate green emission upon 808 nm excitation. Such specially designed UCNPs with switchable green and red emissions are further explored for imaging of latent fingerprint and detection of explosive residues in the fingerprint simultaneously. This work suggests a novel research interest in fine‐tuning of upconversion emissions through precisely controlling energy migration processes of the same lanthanide activator ion. Furthermore, use of these nanoparticles in other applications such as simultaneous dual‐color imaging or orthogonal bidirectional photoactivation can be explored.

Orthogonal Emissive Upconversion Nanoparticles: Material Design and Applications

“…One year later, by manipulating the synergy existing between metal ion (Mn 2+ ) modulation and distance-related energy emigration, this group were able to control the same activator ion (Er 3+ ) energy migration pathway to emit orthogonal emissions. [37] In their work, Mn 2+ ions and Er 3+ ions are mingled in the core UCNPs first that could facilitate red emission under 980 nm excitation. Then the external area of core UCNPs will see the appearance of inner shell (NaYF 4 ) and outer shell (NaNdF 4 ).…”

“…For example, this year Mei's group recently reported one kind of OUCNPs with upconverted red emission and green emission under 980 to 808 nm excitation wavelength. [37] After immersing into the PEI-OUCNPs aqueous solution, the fingerprint pattern can be displayed in two different colors. When the fingerprint pattern attached explosive trinitrotoluene (TNT) residues, PEI-OUCNPs TNT will form Meisenheimer complex which have a strong absorption at 500 nm, which overlaps with the green emission excited under 808 nm wavelength, in other words, the complex will selectively quench the green emission.…”

“…What is more, OUCNPs have the ability to switch emission on demand, so one emission could be designed for imaging, the other emission can be designed to for many applications including PDT, [31,103] delivery, [39] and detection. [37] These imaged guided applications spread the UCNPs' application fields and attract more and more researchers' attention.…”

“…During the last decade, there emerge many proposals relating to various new synthetic approaches. They aims to upgrade the UCNPs into OUCNPs including doping different UCNPs in separate layers, [26] multiple shell containing a layer of photon-inert shell to stop energy moving from one luminescent layer to another, [27,[33][34][35][36] controlling energy migration processes within single lanthanide activator, [37,38] and modularly assembled UCNPs. [30,39] Meanwhile, it is also easy for us to notice the appearance of OUCNPs in some new areas such as reversible photo-switching, [26][27][28][29] super-resolution imaging, [25] bidirectional photoactivation, [38] and programmable therapeutics, [30,32] and many other areas.…”

Intelligent Fe–Mn Layered Double Hydroxides Nanosheets Anchored with Upconversion Nanoparticles for Oxygen‐Elevated Synergetic Therapy and Bioimaging

“…[18,19] It is noteworthy that near-infrared (NIR) light (780-1400 nm) has deeper tissue penetration and lower tissue absorption than visible and ultraviolet light, has therefore been widely utilized in imaging technology. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] Coincidentally, rare-earth ions-based upconversion nanoparticles (UCNPs) are ideal candidates that can convert NIR photons into ultraviolet photons or visible light, thereby avoiding direct damage to tissues by ultraviolet light. [37][38][39][40][41][42][43][44][45][46][47][48][49] After loading a photosensitizer, deep tissue PDT can be realized.…”