Abstract
The availability of colloidal nano-materials with high efficiency, stability, and non-toxicity in the near infrared-II range is beneficial for biological diagnosis and therapy. Rare earth doped nanoparticles are ideal luminescent agents for bio-applications in the near infrared-II range due to the abundant energy level distribution. Among them, both excitation and emission range of Er3+ ions can be tuned into second biological window range. Herein, we report the synthesis of ∼15 nm LiYF4, NaYF4, and NaGdF4 nanoparticles doped with Er3+ ions and their core-shell structures. The luminescent properties are compared, showing that Er3+ ions with single-doped LiYF4 and NaYF4 nanoparticles generate stronger luminescence than Er3+ ions with doped NaGdF4, despite the difference in relative intensity at different regions. By epitaxial growth an inert homogeneous protective layer, the surface luminescence of the core-shell structure is further enhanced by about 5.1 times, 6.5 times, and 167.7 times for LiYF4, NaYF4, and NaGdF4, respectively. The excellent luminescence in both visible and NIR range of these core-shell nanoparticles makes them potential candidate for bio-applications.
Highlights
The 4f-4f transition of rare earth elements endows them with outstanding optical properties
We reported the successful synthesis of three types of fluoride matrix, LiYF4, NaYF4, and NaGdF4, each one doped with Er3+ ions
In order to evaluate the emission intensity impacted by matrix, 10% Er3+ was doped into three matrix LiYF4, NaYF4 and NaGdF4 according to a previous synthesis procedure (Wang et al, 2010b)
Summary
The 4f-4f transition of rare earth elements endows them with outstanding optical properties. The energy of photons can be converted through rational designed transition among their abundant energy levels (Auzel, 2004; Wen et al, 2018). These advantages make rare earth elements perfect candidates for light-triggered diagnostics and therapy (Chen et al, 2014; Shao et al, 2016; Qiang and Wang, 2019; Wang et al, 2020). Due to the nonlinear instincts, UC materials are well-developed for bio-imaging (Gonzalez-Bejar et al, 2016; Chen et al, 2021), photo-dynamics therapy(Lucky et al, 2015; Liu et al, 2019; Jia et al, 2020), and single particle imaging (Gargas et al, 2014; Liu et al, 2017; Zhou et al, 2020b; Dong et al, 2021)
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