Abstract
In recent years, rare earth doped upconversion nanocrystals have been widely used in different fields owing to their unique merits. Although rare earth chlorides and trifluoroacetates are commonly used precursors for the synthesis of nanocrystals, they have certain disadvantages. For example, rare earth chlorides are expensive and rare earth trifluoroacetates produce toxic gases during the reaction. To overcome these drawbacks, we use the less expensive rare earth hydroxide as a precursor to synthesize β-NaYF4 nanoparticles with multiform shapes and sizes. Small-sized nanocrystals (15 nm) can be obtained by precisely controlling the synthesis conditions. Compared with the previous methods, the current method is more facile and has lower cost. In addition, the defects of the nanocrystal surface are reduced through constructing core–shell structures, resulting in enhanced upconversion luminescence intensity.
Highlights
IntroductionLanthanide (Ln3+ )-doped upconversion nanoparticles (UCNPs) that convert low energy photons into high energy photons through a two- or multi-photon absorption mechanism have extensively attracted researchers’ attention due to their potential applications in a variety of fields, such as bioimaging [1,2,3,4,5,6,7,8], biosensing [9,10], drug delivery [11,12], and cancer therapy [13,14,15,16].Compared with traditional fluorescent probes, such as organic fluorescent dyes and semiconductor quantum dots, UCNPs possess some unique advantages, including weak background fluorescence, large anti-Stokes shift, high photochemical stability, narrow emission bandwidth, long luminescent lifetime, high penetration depth, and low toxicity, among others [17,18,19,20,21,22,23,24]
To clarify the role of Na sodium oleate (NaOA), we further studied the effect of its amount on the synthesis of
The size and morphology of the products were manipulated through the precise tuning of the ratio of Na+ /Ln3+ /F−, the ratio of oleic acid (OA)/ODE, and the quantity of the NaOA
Summary
Lanthanide (Ln3+ )-doped upconversion nanoparticles (UCNPs) that convert low energy photons into high energy photons through a two- or multi-photon absorption mechanism have extensively attracted researchers’ attention due to their potential applications in a variety of fields, such as bioimaging [1,2,3,4,5,6,7,8], biosensing [9,10], drug delivery [11,12], and cancer therapy [13,14,15,16].Compared with traditional fluorescent probes, such as organic fluorescent dyes and semiconductor quantum dots, UCNPs possess some unique advantages, including weak background fluorescence, large anti-Stokes shift, high photochemical stability, narrow emission bandwidth, long luminescent lifetime, high penetration depth, and low toxicity, among others [17,18,19,20,21,22,23,24]. Among reported UCNPs, hexagonal phase (β-) sodium yttrium fluoride has been shown to be one of most efficient host materials owing to its low photon cutoff energy (~350 cm−1 ) and high chemical stability, which are able to effectively reduce non-radiative energy losses at the intermediate states of lanthanide ions [25]. Several methods have been reported to synthesize lanthanide-doped β-NaYF4 nanoparticles with controlled crystalline phase, shape, and size. Solvothermal method and thermal decomposition methods are two of the most frequently used techniques to synthesize monodisperse lanthanide-doped β-NaYF4 nanoparticles. Capobianco and co-workers synthesized β-NaYF4 nanocrystals co-doped with Yb3+ /Er3+ or Yb3+ /Tm3+ via the thermal decomposition of rare earth trifluoroacetate
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