Continuous Flow Synthesis of Persistent Luminescent Chromium-Doped Zinc Gallate Nanoparticles

Abstract

Near-infrared persistent luminescent (or afterglow) nanoparticles with the biologically appropriate size are promising materials for background-free imaging applications, while the conventional batch synthesis hardly allows for reproducibility in controlling particle size because of the random variations of reaction parameters. Here, highly efficient chemistry was matched with an automated continuous flow approach for directly synthesizing differently sized ZnGa2O4:Cr3+ (ZGC) nanoparticles exhibiting long persistent luminescence. The key flow factors responsible for regulating the particle formation process, especially the high pressure–temperature and varied residence time, were investigated to be able to tune the particle size from 2 to 6 nm and to improve the persistent luminescence. Upon silica shell encapsulation of the nanoparticles accompanied by an annealing process, the persistent luminescence of the resulting particles was remarkably enhanced. High-fidelity automated flow chemistry demonstrated here offers an alternative for producing ZGC nanoparticles and will be helpful for other compositionally complex metal oxide nanoparticles.

Molten Salt Synthesis of Persistent Luminescent/Magnetic Cr3+-Doped Zinc Gallogermanate Particles

“…The emission band centered at 695 nm accounts for the deep red persistent luminescence of Cr 3+ dopants. 34 The excitation spectrum monitored at 695 nm covers a broad spectral region (from 230 to 500 nm), where the dominant excitation peak at 260 nm can be attributed to the band-to-band transition of the ZGGO host, while the 407 nm excitation band originates from the inner 4 A 2 -4 T 1 transition of Cr 3+ dopants (Figure S12). 21 The luminescent quantum yield for as-prepared ZGGO particles was determined to be ∼23.6%.…”

Semiconductor Nanocrystals Emitting in the Second Near‐Infrared Window: Optical Properties and Application in Biomedical Imaging

“…[183] The use of phosphorescence signals (a long-lived PL) in the NIR-II window allows for some additional benefits for imaging in dynamic physiological environments. [184][185][186] Long-lived CuInSe 2 -based NIR-II phosphorescent nanoprobes were used by Cheng and co-workers for in vivo tumor imaging and visualization of high-order branches of blood vessels. [166,186] Solvent-induced aggregation resulted in the appearance of strong NIR-II phosphorescence at the wavelengths up to 1045 nm.…”

Design of need-based phosphors and scintillators by compositional modulation in the ZnGa2−xAlxO4:Cr3+ spinel: pure compound versus solid solutions

“…[6][7][8] In the past years, chromium-activated ZnGa 2 O 4 is being considered as one of the most fascinating optical materials due to its outstanding and bright near-infrared photoluminescence, efficient persistent luminescence, long afterglow, high light harvesting efficiency, wavelength tunability, and superior photostability. 2,3,[9][10][11][12][13] Consequently, ZnGa 2 O 4 :Cr 3+ (ZGOC) has found wide range applications in areas such as bioimaging, optical sensors, optical information storage, drug delivery, and plant growth. 2,9,10,13,14 However, there is still continuous ongoing effort in the global research community to explore more functionalities, add new dimensions, and improve the optical properties of ZGOC nanoparticles.…”