Controlled synthesis, formation mechanism, and great enhancement of red upconversion luminescence of NaYF4:Yb3+, Er3+ nanocrystals/submicroplates at low doping level.
ABSTRACT Strong red upconversion luminescence of rare-earth ions doped in nanocrystals is desirable for the biological/biomedical applications. In this paper, we describe the great enhancement of red upconversion emission (4F9/2 --> I15/2 transition of Er3+ ion) in NaYF4:Yb3+, Er3+ nanocrystals at low doping level, which is ascribed to the effectiveness of the multiphonon relaxation process due to the existence of citrate as a chelator and cross relaxation between Er3+ ions. The dissolution-recrystallization transformation, governing both the intrinsic crystalline phase (cubic and/or hexagonal phase) and the growth regime (thermodynamic vs kinetic), is responsible for the phase control of the NaYF4 crystals. The possible formation mechanism of the NaYF4 crystals and the role of trisodium citrate which acts as a chelating agent and shape modifier are discussed in detail. It is also found that the alpha --> beta phase transition is favored by the high molar ratio of fluoride to lanthanide and high hydrothermal temperature as well as long hydrothermal time.
Article: Control of Green and Red Upconversion in NaYF4:Yb3+,Er3+ Nanoparticles by Excitation Modulation.[show abstract] [hide abstract]
ABSTRACT: Control of the two strongest upconversion emission lines in NaYF4:Yb3+, Er3+ nanoparticles is demonstrated by varying the excitation repetition rate. This technique may enable new multiplexed sensing modalities based on multicolor luminescent nanoparticles, currently contemplated for biomedical imaging and diagnostics.Journal of Materials Chemistry 01/2011; 21(46):18530-18533. · 5.97 Impact Factor
[show abstract] [hide abstract]
ABSTRACT: New generation fluorophores, also termed upconversion nanoparticles (UCNPs), have the ability to convert near infrared radiations with lower energy into visible radiations with higher energy via a nonlinear optical process. Recently, these UCNPs have evolved as alternative fluorescent labels to traditional fluorophores, showing great potential for imaging and biodetection assays in both in vitro and in vivo applications. UCNPs exhibit unique luminescent properties, including high penetration depth into tissues, low background signals, large Stokes shifts, sharp emission bands, and high resistance to photobleaching, making UCNPs an attractive alternative source for overcoming current limitations in traditional fluorescent probes. In this article, we discuss the recent progress in the synthesis and surface modification of rare-earth doped UCNPs with a specific focus on their biological applications. FROM THE CLINICAL EDITOR: Upconversion nanoparticles - a new generation of fluorophores - convert near infrared radiations into visible radiations via a nonlinear optical process. These UCNPs have evolved as alternative fluorescent labels with great potential for imaging and biodetection assays in both in vitro and in vivo applications.Nanomedicine: nanotechnology, biology, and medicine 03/2011; 7(6):710-29. · 5.44 Impact Factor