Ultrasmall Monodisperse NaYF₄:Yb³⁺/Tm³⁺ Nanocrystals with Enhanced Near-Infrared to Near-Infrared Upconversion Photoluminescence

Abstract

Photoluminescent NaYF4:Yb3+/Tm3+ nanocrystals are ideally suited for in vitro and in vivo photoluminescence (PL) bioimaging due to their virtue of near infrared to near infrared (NIR-to-NIR) upconversion (UC); they display PL with peak at ~800 nm if excited at ~980 nm. Here, we report the synthesis of monodisperse NaYF4:Yb3+/Tm3+ nanocrystals of ultrasmall size (7–10 nm) with high UC efficiency. The intensity of their NIR UC emission was demonstrated to increase by up to 43 times along with increase in relative content of Yb3+ ions from 20% to 100%, with a corresponding decrease in the Y3+ content from 80% to 0%. The achieved ultrasmall NaYbF4:2% Tm3+ nanocrystals manifest NIR PL emission, which is 3.6 times more intense than that from 25-30 nm sized NaYF4: 20% Yb3+/2% Tm3+ nanocrystals, previously synthesized and used for in vitro and in vivo bioimaging. An optimization of both size and UC PL efficiency of NIR-to-NIR nanocrystals provides us with highly efficient optical imaging probes for bioapplications.

Excitation energy migration dynamics in upconversion nanomaterials

“…Chen et al reported that in ultrasmall (7-10 nm) NaYF 4 :x%Yb 3+ ,2%Tm 3+ nanoparticles, the Yb 3+ ions can be doped with concentrations as high as 98% before obvious quenching occurs. 27 The NIR upconversion emission of Tm 3+ at 808 nm was demonstrated to increase up to 43 times along with an increase in the relative content of Yb 3+ ions from 20% to 98%, which was ascribed to the electronic characteristics of the sensitizer Yb 3+ being different from the activators, such as Er 3+ , Tm 3+ or Ho 3+ . As introduced before, the energy scheme of Yb 3+ is relatively simple and there is only one excited state 2 F 5/2 in the energy range of interest.…”

Tailored Near‐Infrared Photoemission in Fluoride Perovskites through Activator Aggregation and Super‐Exchange between Divalent Manganese Ions

“…Recently, the most vibrant field of interest in this context has been in the area of biomedical imaging, where cells and tissue exhibit weak autofluorescence and low transmission loss for optical signals just within the NIR 22, 23. It has hence been crucial to design (nano) materials that exhibit both emission and excitation of luminescence in the NIR region for in vitro and in vivo imaging applications 24, 25. For example, rare‐earth‐doped nanocrystals have attracted considerable interest in recent years as potential candidates for high‐resolution bioimaging because such nanocrystals may exhibit NIR upconversion (UC) emission upon excitation by a 976 nm laser diode (LD) 26, 27, 28, 29.…”

Recent Advances on Functionalized Upconversion Nanoparticles for Detection of Small Molecules and Ions in Biosystems

“…Although this phenomenon has been known more than 60 years,29 for a long time, the application of this phenomenon was only limited to bulk glass and crystalline materials 30, 31. Until the late 1990s, the advance of nanotechnology provided new opportunities to UCNPs and these materials have become one of the most attractive research fields within nanoscience community including many progresses in biodetection 32, 33, 34, 35, 36…”