Showing papers by "Xueyuan Chen published in 2010"

Upconversion nanoparticles in biological labeling, imaging, and therapy

Abstract: Upconversion refers to non-linear optical processes that convert two or more low-energy pump photons to a higher-energy output photon. After being recognized in the mid-1960s, upconversion has attracted significant research interest for its applications in optical devices such as infrared quantum counter detectors and compact solid-state lasers. Over the past decade, upconversion has become more prominent in biological sciences as the preparation of high-quality lanthanide-doped nanoparticles has become increasingly routine. Owing to their small physical dimensions and biocompatibility, upconversion nanoparticles can be easily coupled to proteins or other biological macromolecular systems and used in a variety of assay formats ranging from bio-detection to cancer therapy. In addition, intense visible emission from these nanoparticles under near-infrared excitation, which is less harmful to biological samples and has greater sample penetration depths than conventional ultraviolet excitation, enhances their prospects as luminescent stains in bio-imaging. In this article, we review recent developments in optical biolabeling and bio-imaging involving upconversion nanoparticles, simultaneously bringing to the forefront the desirable characteristics, strengths and weaknesses of these luminescent nanomaterials.

A Strategy to Achieve Efficient Dual-Mode Luminescence of Eu3+ in Lanthanides Doped Multifunctional NaGdF4 Nanocrystals

Abstract: Trivalent lanthanide (Ln 3 + ) ions doped luminescent nanocrystals (NCs) of various compositions, albeit most of their bulk counterparts have been well studied previously, have attracted reviving interest and come to the forefront in nanophotonics owing to their distinct electrical, optical and magnetic properties as well as their potential applications in diverse fi elds such as LEDs, lasers, biological labeling and imaging. [ 1 ] Compared to conventional luminescent materials such as organic fl uorescent dyes and quantum dots (QDs), these Ln 3 + doped NCs show more superior features including narrow emission band widths ( < 10 nm), [ 2 ] long luminescence lifetime ( μ s–ms range) [ 2b,c ] and low long-term toxicity. [ 3 ] These features coupled with the higher resistance to photobleaching relative to that of organic fl uorescent dyes make them highly suitable for use as alternatives to organic fl uorescent dyes and QDs for various biological applications. In particular, inorganic fl uorides have the advantages of high chemical stability and intrinsic low phonon energies ( ∼ 350 cm − 1 ), and thereby are often employed as host materials for the doping of Ln 3 + to achieve the desirable downconversion (DC) or upconversion (UC) luminescence of Ln 3 + . [ 4 ] Because of well-established effi cient UC luminescence, considerable efforts have been devoted to the synthesis and multicolor tuning of Ln 3 + -doped NaYF 4 UC NCs, where Yb 3 + acting as the sensitizer with a large absorption cross-section at ∼ 980 nm is usually codoped along with the most common UC activator ions (Er 3 + , Tm 3 + and Ho 3 + ) to produce strong red, green, and violet UC emissions. [ 5 ]

Determination of Judd-Ofelt intensity parameters from the excitation spectra for rare-earth doped luminescent materials.

Abstract: By utilizing the proportional relationship between the excitation and absorption spectra for some special excited multiplets of rare-earth (RE) ions that are followed by a very fast nonradiative relaxation to the monitored level, we propose a new approach to determine the Judd-Ofelt (JO) intensity parameters that are crucial to the evaluation of laser and luminescent materials via excitation spectra. To validate this approach, the JO parameters of NaGd(WO(4))(2) : Er(3+) and YLiF(4) : Nd(3+) crystals are calculated and compared through both the excitation and absorption spectra. The JO parameters derived from this approach are in good agreement with that determined from the conventional method (absorption spectra). Furthermore, the JO intensity parameters of Y(2)O(3) : Er(3+) nanocrystals are derived from the excitation spectra by taking into account the nano-size effects, which are comparable to the values of the crystal counterpart. The proposed approach is of particular importance for those powders or nanophosphors with low RE doping concentration that their quantitative absorption spectra are difficult to measure.

Eu3+-Doped In2O3 Nanophosphors: Electronic Structure and Optical Characterization

Abstract: Rare-earth ion-doped semiconducting nanocrystals have attracted extensive attention due to the ability to tailor their optical properties via size control and to achieve efficient luminescence through the host sensitization. A new type of nanophosphor based on Eu3+-ion-doped In2O3 nanocrystals, synthesized via a facile solvothermal method, shows intense and well-resolved intra4f emissions of Eu3+ upon bandgap excitation. Optical properties of Eu3+ occupying two crystallographic sites (C2 and S6) are systematically investigated by means of high-resolution emission and excitation spectra at 10−300 K. The crystal-field (CF) analysis and Judd−Ofelt (JO) intensity calculation of Eu3+ at C2 site yield relatively large CF strength and JO intensity parameters, indicating the good optical performance of this nanophosphor. Due to a small filling factor (0.43) of the In2O3 nanocrystals, the radiative lifetime of 5D0 of Eu3+ is found to be significantly affected by the surrounding media with various refractive indice...

Optical properties of Nd3+ ion-doped ZnO nanocrystals.

Abstract: Hexagonal Nd(3+)-doped ZnO nanocrystals with multiple luminescent centers were synthesized by means of a facile sol-gel method. The Nd(3+)-doped ZnO nanocrystals were characterized by using the X-ray diffraction, transmission electron microscopy, ultraviolet-visible reflectance spectra, and fluorescence spectroscopy. Host-to-Nd3+ energy transfer was observed for the first time in Nd(3+)-doped ZnO nanocrystals. It was found that Nd3+ ions can be effectively sensitized by the ZnO nanocrystals, resulting in sharp and intense characteristic Nd3+ luminescence. The photoluminescence (PL) and PL excitation spectra of Nd3+ ions in the ZnO nanocrystals were investigated in detail. Furthermore, the possible mechanism of host-to-Nd3+ energy transfer was also proposed on the basis of the optical properties of Nd3+ ions in the ZnO nanocrystals.

Optical Spectroscopy of Sm3+ and Dy3+ Doped ZnO Nanocrystals

Abstract: Sm3+ and Dy3+ ions doped hexagonal wurtzite ZnO nanocrystals were fabricated by a sol-gel method The obtained ZnO nanocrystals were characterized using the X-ray diffraction, transmission electron microscopy, ultraviolet-visible reflectance spectra, and low-temperature luminescence spectroscopy Intense and well resolved emission lines for Sm3+ and Dy3+ ions can be achieved via an energy transfer process from ZnO host to the dopants It was found that the host sensitized emissions were more efficient than that of direct excitation for Sm3+ and Dy3+ ions Moreover, multiple sites of Sm3+ and Dy3+ ions in ZnO nanocrystals were identified based on the low-temperature photoluminescence spectra

Poly (acrylic acid)-capped lanthanide-doped BaFCl nanocrystals: synthesis and optical properties

Abstract: Water-soluble lanthanide-doped BaFCl nanophosphors with the surface functionalized by a layer of poly (acrylic acid) are synthesized via a facile one-step solvothermal method. Intense long-lived luminescence is realized from visible to near-infrared (NIR) by doping with different lanthanide ions. The emission and excitation spectra of Eu3+ indicate that the doped lanthanide ions occupy a site close to the surface of the nanoparticles. Strong NIR emissions of Nd3+ and green luminescence of Tb3+ using Ce3+ as sensitizers are also achieved in BaFCl nanoparticles. The synthesized nanoparticles featuring long-lived luminescence in either visible or NIR regions may have potential applications as luminescent labels for biological applications.

Optical spectroscopy of rare earth ion-doped TiO2 nanophosphors.

Abstract: Trivalent rare-earth (RE3+) ion-doped TiO2 nanophosphors belong to one kind of novel optical materials and have attracted increasing attention. The luminescence properties of different RE3+ ions in various TiO2 nanomaterials have been reviewed. Much attention is paid to our recent progresses on the luminescence properties of RE3+ (RE = Eu, Er, Sm, Nd) ions in anatase TiO2 nanoparticles prepared by a sol-gel-solvothermal method. Using Eu3+ as a sensitive optical probe, three significantly different luminescence centers of Eu3+ in TiO2 nanoparticles were detected by means of site-selective spectroscopy at 10 K. Based on the crystal-field (CF) splitting of Eu3+ at each site, C2v and D2 symmetries were proposed for Eu3+ incorporated at two lattice sites. A structural model for the formation of multiple sites was proposed based on the optical behaviors of Eu3+ at different sites. Similar multi-site luminescence was observed in Sm(3+)- or Nd(3+)-doped TiO2 nanoparticles. In Eu(3+)-doped TiO2 nanoparticles, only weak energy transfer from the TiO2 host to the Eu3+ ions was observed at 10 K due to the mismatch of energy between the TiO2 band-gap and the Eu3+ excited states. On the contrary, efficient host-sensitized luminescences were realized in Sm(3+)- or Nd(3+)-doped anatase TiO2 nanoparticles due to the match of energy between TiO2 band-gap and the Sm3+ and Nd3+ excited states. The excitation spectra of both Sm(3+)- and Nd(3+)-doped samples exhibit a dominant broad peak centered at approximately 340 nm, which is associated with the band-gap of TiO2, indicating that sensitized emission is much more efficient than direct excitation of the Sm3+ and Nd3+ ions. Single lattice site emission of Er3+ in TiO2 nanocrystals can be achieved by modifying the experimental conditions. Upon excitation by a Ti: sapphire laser at 978 nm, intense green upconverted luminescence was observed. The characteristic emission of Er3+ ions was obtained both in the ultraviolet-visible (UV-vis) and near-infrared regions through the high-resolution experiments at 10 K. The CF experienced by Er3+ in TiO2 nanocrystal was systematically studied by means of the energy level fitting.

Sensitized Luminescence of Sm3+,Eu3+-Codoped TiO2 Nanoparticles

Abstract: Sm3+,Eu(3+)-codoped TiO2 nanoparticles were prepared by a facile sol-gel-solvothermal method. Sm3+ and Eu3+ were successfully incorporated into a TiO2 lattice and resulted in intense emission lines with resolved crystal-field splitting, in spite of a large mismatch in ionic radius between trivalent lanthanides (Ln3+) and Ti4+. The intense sensitized emissions of Sm3+ and Eu3+ ions by TiO2 host were obtained at room temperature. In this case, Sm3+ also acts as a bridge to transfer energy from TiO2 host to Eu3+ ions, which was not observed in Eu(3+)-doped TiO2 nanoparticles. In comparison with direct excitation of lanthanide ions, the luminescence lifetimes of 4G5/2 of Sm3+ and 5D0 of Eu3+ were observed to be significantly prolonged upon excitation above TiO2 band-gap. A sensitization mechanism to illustrate the energy transfer from TiO2 to Sm3+ and Eu3+ was proposed based on the optical behaviors of the codoped nanoparticles.

Rare-earth oxide nanostructures: rules of rare-earth nitrate thermolysis in octadecylamine.

Abstract: The decomposed regularity of rare-earth nitrates in octadecylamine (ODA) is discussed. The experimental results show that these nitrates can be divided into four types. For rare-earth nitrates with larger RE(3+) ions (RE=rare earth, La, Pr, Nd, Sm, Eu, Gd), the decomposed products exhibited platelike nanostructures. For those with smaller RE(3+) ions (RE=Y, Dy, Ho, Er, Tm, Yb), the decomposed products exhibited beltlike nanostructures. For terbium nitrate with a middle RE(3+) ion, the decomposed product exhibited a rodlike nanostructure. The corresponding rare-earth oxides, with the same morphologies as their precursors, could be obtained when these decomposed products were calcined. For cerium nitrate, which showed the greatest differences, flowerlike cerium oxide could be obtained directly from decomposition of the nitrate without further calcination. This regularity is explained on the basis of the lanthanide contraction. Owing to their differences in electron configuration, ionic radius, and crystal structure, such a nitrate family therefore shows different thermolysis properties. In addition, the potential application of these as-obtained rare-earth oxides as catalysts and luminescent materials was investigated. The advantages of this method for rare-earth oxides includes simplicity, high yield, low cost, and ease of scale-up, which are of great importance for their industrial applications.

Optical Spectroscopy of Sm 3þ and Dy 3þ Doped ZnO Nanocrystals

Abstract: Sm 3þ and Dy 3þ ions doped hexagonal wurtzite ZnO nanocrys- tals were fabricated by a sol-gel method. The obtained ZnO nanocrystals were characterized using the X-ray diffraction, transmission electron microscopy, ultraviolet-visible reflectance spectra, and low-temperature luminescence spectroscopy. Intense and well resolved emission lines for Sm 3þ and Dy 3þ ions can be achieved via an energy transfer process from ZnO host to the dopants. It was found that the host sensitized emissions were more efficient than that of direct excitation for Sm 3þ and Dy 3þ ions. Moreover, multiple sites of Sm 3þ and Dy 3þ ions in ZnO nanocrystals were

Erbium ion-doped tin dioxide nanocrystal near-infrared light-emitting material and preparation method and application thereof

Abstract: Preparation of an erbium ion-doped tin dioxide nanocrystal near-infrared light-emitting material relates to a nano fluorescent material. The component of the erbium ion-doped tin dioxide nanocrystal prepared by the invention is xEr3+-(1-x)SnO2 (x=0.001-2mol%). The light-emitting material adopts the tin dioxide substrate to sensitize the erbium ion to emit light, uses a fluorescence spectrometer to test light emitting of the samples and can utilize energy transfer from the SnO2 substrate to Er3+ by selecting excitation of SnO2 band gaps, thus realizing strong near-infrared light emitting under room temperature of the Er3+ ion in the position of 1.55mu m.