Abstract

Water‐soluble NaYF4:Yb3+, Er3+ nanoparticles (NPs) are successfully prepared by a solvothermal reaction using branched polyethylenimine (PEI) with different chain lengths as the surfactants in a water/diethylene glycol (DEG) mixed solution. It is shown that the size of NaYF4 NPs prepared with high molecular weight PEI (HPEI) is smaller than that of the NPs prepared with low molecular weight (LPEI), while small‐sized NPs exhibit more intense upconversion luminescence intensities than large‐sized NPs in the same excitation power of 980 nm. It is found that HPEI is conducive to the formation of smaller NP with high crystallinity. Small‐sized NaYF4:Yb3+, Er3+ NPs with intense upconversion luminescence and improved crystallinity were related to their growth process. A possible growth mechanism of the samples is proposed. The results of this study can provide new insights into the controlled synthesis of novel NPs.

Highlights

  • In recent years, the upconversion luminescence of rareearth fluoride NPs has attracted great research interest of the research groups in the world due to their potential applications in various fields, such as photodetectors and fluorescent labels or imaging probes [1,2,3,4,5,6,7]

  • The size of the NPs prepared with high molecular weight PEI (HPEI) is smaller than that of the NPs prepared with LPEI via the same solvothermal treatment process

  • The diffusion rate of the cations bound to HPEI molecules in solution is slower than that of the cations bound to LPEI molecules, with the result that the growth rate of the NaYF4 NPs prepared with HPEI is slower than that of the NPs prepared with LPEI

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Summary

Introduction

The upconversion luminescence of rareearth fluoride NPs has attracted great research interest of the research groups in the world due to their potential applications in various fields, such as photodetectors and fluorescent labels or imaging probes [1,2,3,4,5,6,7]. In order to carry out their widespread application in biomedical fields, the upconversion luminescence NPs should be small enough and water soluble and exhibit high fluorescent intensity. It is important to develop efficient and convenient methods to synthesize NaYF4:Yb, Er NPs with high quality and monodispersion for various biomedical applications. A possible growth mechanism of the samples is proposed These nanocrystals have great potential for use in biology and medicine as fluorescent labels or imaging probes

Experimental Section
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