Squaraine Dye-Sensitized Upconversion with Enhanced Stability and Minimized Aggregation-Caused Quenching

Abstract

Upconversion nanoparticles (UCNPs) doped with lanthanides have limited brightness due to their small absorption cross section to light. However, using organic sensitizers can significantly enhance their light absorption ability. Unfortunately, the practical application of organic sensitizers has been hindered by poor stability and aggregation-caused quenching (ACQ). To address these issues, we developed a novel squaraine-based dye, SQ-739, for sensitizing upconversion luminescence (UCL). This dye has a maximum absorption at 739 nm, and shows 1 order of magnitude and 2-fold improved chemical-and photostability, compared to the commonly used cyanine-based dye IR-806, respectively. When SQ-739 is used to sensitize UCNPs, the resulting SQ-739-UCNPs exhibit excellent photostability and reduced ACQ in the presence of polar solvents. Moreover, at the single particle level, the SQ-739-UCNPs exhibit a 97-fold increase in UCL emission compared to bare UCNPs. This squaraine dye-based system represents a new design strategy for developing highly stable and efficient NIR upconversion probes.

Upconversion as a spear carrier for tuning photovoltaic efficiency

“…For example, the 4 I 11/2 state of Er 3+ overlaps with the 2 F 5/2 state of Yb 3+ and allows energy transfer from Er to Yb. 55,56 The role of the emitter is to convert the photons with low energy into higher-energy photons. Therefore, sensitizer atoms having f–f transitions among different energy levels that could provide the required emission wavelength have to be chosen accordingly.…”

Recent Advances in Triplet Energy Transfer between Organic Dyes and Lanthanide-Doped Luminescent Nanoparticles

“…(f) Molecular structure of the squaraine dye SQ-739. Reprinted with permission from ref . Copyright 2023 American Chemical Society.…”

“…The locations of the particles are indicated by yellow circles on the right picture. Reprinted with permission from ref . Copyright 2023 American Chemical Society.…”

“…(h) The single particle intensity of SQ-739-UCNPs and UCNPs in oleic acid under 721 nm excitation. Reprinted with permission from ref . Copyright 2023 American Chemical Society.…”

Amplifying Photon Upconversion in Alloyed Nanoparticles for a Near-Infrared Photodetector

“…Nevertheless, these methods are costly and have rigorous technical requirements for optical/plasmonic nanostructures. Alternatively, the upconverison luminescence could also be improved by optimizing the material itself via surface passivation, − dye sensitization, − crystal engineering, − a high doping concentration, − and energy flux manipulation . These advances presented an easy way to enhance upconversion of UCNPs and promoted their diverse photonics applications. − Despite these efforts, enhancing the upconversion intensity and quantum efficiency of UCNPs in particular at sub-watts per square centimeter irradiance is still challenging.…”