Xianping Fan

Luminescent nanomaterials for biological labelling

The use of labelling or staining agents has greatly assisted the study of complex biological interactions in the field of biology. In particular, fluorescent labelling of biomolecules has been demonstrated as an indispensable tool in many biological studies. Types of fluorescent labelling agents that are commonly used include conventional classes of organic fluorophores such as fluorescein and cyanine dyes, as well as newer types of inorganic nanoparticles such as QDs, and novel fluorescent latex/silica nanobeads. The newer classes of fluorescent labels are gaining increasing popularity in place of their predecessors due to their better optical properties such as possessing an enhanced photostability and a larger Stokes shift over conventional organic fluorophores, for example. This paper gives an overview of the recent advances on these luminescent nanomaterials with emphases on their optical characteristics that are crucial in fluorescence microscopy, both advantages and limitations in their usage as well as challenges they face, and puts forward the future direction of fluorescent labels in the area of biolabelling.

One-pot synthesis of chitosan/LaF3:Eu3+ nanocrystals for bio-applications

Lanthanide-based nanocrystals have shown great potential to be used as luminescent materials but their biological applications have been limited because most of the nanocrystals synthesized so far are not water soluble or biocompatible. We report a very straightforward method to synthesize water soluble and biocompatible LaF3 nanocrystals doped with Eu3+ via facile co-precipitation with a natural biopolymer, chitosan. The nanocrystals are very fluorescent and have a small size of about 20 nm. Chitosan is found to cap the nanocrystals during the synthesis process, which renders them water soluble and biocompatible, and provides functional groups such as hydroxyl and amino groups for further attachment of biomolecules. The nanocrystals remain stable in aqueous solution with pH ranging from 2 to 7.4. The nanocrystals are very suitable for use in biological applications, for example, intracellular labelling or measurements, because they are very small in size.

Facile synthesis of water-soluble LaF3∶ Ln3+ nanocrystals

Water-soluble lanthanide-doped LaF3 nanocrystals were synthesized using a simple method carried out in aqueous solution at low temperature. The nanocrystals have a nearly spherical shape and an average size of below 30 nm. They consisted of well crystallized hexagonal phases. The luminescence quantum efficiency was about 16% in aqueous solution. LaF3 nanocrystals doped with different lanthanide ions (Eu3+, Ce3+, Tb3+, and Nd3+) were synthesized, which showed strong luminescence in the visible (VIS) and near-infrared (NIR) spectral regions.

Laser properties and photostabilities of laser dyes doped in ORMOSILs

Laser dyes such as rhodamine B, rhodamine 6G, pyrromethene 567, perylene orange and perylene red were doped into GPTMS-, MTES- and VTES-derived organically modified silicates (ORMOSILs) by sol–gel process. A longitudinal pumped solid-state dye laser was established with a Q-switched Nd:YAG laser source. The lifetimes of these dyes in various ORMOSILs were investigated by using such an experimental setup at a pump repetition rate of 2 Hz and pump intensity of 0.1 or 1.4 J/cm 2 . The lifetime of 60 000 pulses, 50 GJ/mol in normalized photostability, was obtained for the pyrromethene 567 doped in MTES-derived ORMOSIL with the net sample thickness of 4 mm when its output energy declined to 50% of its initial value. The slope efficiencies of pyrromethene 567 and perylene orange in various host media were also measured. � 2003 Elsevier B.V. All rights reserved.

Judd-Ofelt analysis and luminescence behavior of Er3+ ions in glass ceramics containing SrF2 nanocrystals

The upconversion luminescence and near infrared luminescence of the Er3+ ions in transparent oxyfluoride glass ceramics containing SrF2 nanocrystals have been investigated. The formation of SrF2 nanocrystals in the glass ceramics was confirmed by x-ray diffraction. The oscillator strengths for several transitions of the Er3+ ions in the glass and glass ceramics have been obtained and then the Judd-Ofelt parameters were determined. The split near infrared emission peaks of the Er3+ ions in the glass ceramics can be observed because the Er3+ ions have been incorporated into crystalline environment of the SrF2 nanocrystals. The upconversion luminescence intensity of Er3+ ions in the glass ceramics increased significantly with the increasing crystallization time. The transition mechanisms of the green and red upconversion luminescence have been ascribed to two-photon process and the blue upconversion luminescence to three-photon process.

Near-infrared emission of Yb 3+ through energy transfer from ZnO to Yb 3+ in glass ceramic containing ZnO nanocrystals

Yb(3+)-doped glass and glass ceramic containing ZnO nanocrystals were prepared by the melting-quenching method and subsequent heat treatment. Intense near-IR emission around 1000 nm that originated from the transition of Yb(3+):(2)F(5/2)→(2)F(7/2) was generated as a result of energy transfer from oxygen interstitials in ZnO nanocrystals to Yb(3+) with energy transfer efficiency of about 10%. The quantum yield for the near-IR emission of Yb(3+) under the excitation of 390 nm was about 16.7%. These materials have potential application in achieving high-efficiency Si solar cells via spectrum modification.

Spectroscopic properties of Er3+ doped glass ceramics containing Sr2GdF7 nanocrystals

The Er3+ doped transparent oxyfluoride glass ceramics containing Sr2GdF7 nanocrystals were prepared and their spectroscopic properties were discussed. The formation of Sr2GdF7 nanocrystals in the glass ceramics was confirmed by x-ray diffraction. The split peaks of the upconversion and near infrared emission bands of the Er3+ doped glass ceramics can be observed. The upconversion luminescence intensity of Er3+ in the glass ceramics increased significantly with the increasing heat treated temperature. The luminescence decay curves and time-resolved spectra indicated that the lifetime of the S3∕24 state of Er3+ in the glass ceramic was longer than that in the glass.The Er{sup 3+} doped transparent oxyfluoride glass ceramics containing Sr{sub 2}GdF{sub 7} nanocrystals were prepared and their spectroscopic properties were discussed. The formation of Sr{sub 2}GdF{sub 7} nanocrystals in the glass ceramics was confirmed by x-ray diffraction. The split peaks of the upconversion and near infrared emission bands of the Er{sup 3+} doped glass ceramics can be observed. The upconversion luminescence intensity of Er{sup 3+} in the glass ceramics increased significantly with the increasing heat treated temperature. The luminescence decay curves and time-resolved spectra indicated that the lifetime of the {sup 4}S{sub 3/2} state of Er{sup 3+} in the glass ceramic was longer than that in the glass.

Local vibration around rare earth ions in alkaline earth fluorosilicate transparent glass and glass ceramics using Eu3+ probe

Abstract By heat treating the alkaline earth fluorosilicate glass, transparent glass ceramics containing alkaline earth fluoride nanocrystallites were prepared. The luminescence spectra and phonon sideband associated with the Eu 3+ : 5 D 2 → 7 F 0 in glass and glass ceramics were investigated to analyze the local environment around Eu 3+ . Judd-Ofelt parameters were also calculated from emission spectra, which indicated that the Eu 3+ ions entered the precipitated CaF 2 , SrF 2 , and BaF 2 nanocrystallites. Heat treating could not pledge Eu 3+ ions to coordinate with F − in the precipitated MgF 2 nanocrystallites, owing to the smaller radius of Mg 2+ than that of Eu 3+ .

Hydrothermal synthesis and luminescence behavior of lanthanide-doped GdF/sub 3/ nanoparticles

The lanthanide-doped GdF₃ nanoparticles have been produced by a simply hydrothermal synthesis procedure. The excitation and emission spectra of the Eu³⁺-doped GdF₃ nanoparticles showed that the excitation energy of Gd³⁺ is efficiently transferred to Eu³⁺ in the Eu³⁺-doped GdF₃ nanoparticles. Due to very low phonon energies of GdF ₃ matrix, the ⁵D₁ emission of Eu³⁺ ions in the Eu³⁺-doped GdF₃ nanoparticles can be observed at room temperature when the doping concentration of Eu ³⁺ ions is lower than 15 mol%. The luminescence intensity of the Eu³⁺-doped GdF₃ nanoparticles increased with increasing concentration of Eu³⁺ ions and reached a maximum at approximately 15 mol%. The Er³⁺-doped GdF₃ nanoparticles exhibit the typical emission spectra of Er³⁺ in the near-infrared region. The upconversion emission of the Er³⁺/Yb³⁺ codoped GdF₃ nanoparticles can also be observed. However, the upconversion emission intensity of the Er³⁺/Yb³⁺-codoped GdF₃ nanoparticles was much weaker than that of the Er³⁺/Yb³⁺-codoped GdF₃ bulk crystal

Establishing the Structural Integrity of Core–Shell Nanoparticles against Elemental Migration using Luminescent Lanthanide Probes

Core-shell structured nanoparticles are increasingly used to host luminescent lanthanide ions but the structural integrity of these nanoparticles still lacks sufficient understanding. Herein, we present a new approach to detect the diffusion of dopant ions in core-shell nanostructures using luminescent lanthanide probes whose emission profile and luminescence lifetime are sensitive to the chemical environment. We show that dopant ions in solution-synthesized core-shell nanoparticles are firmly confined in the designed locations. However, annealing at certain temperatures (greater than circa 350 °C) promotes diffusion of the dopant ions and leads to degradation of the integrity of the nanoparticles. These insights into core-shell nanostructures should enhance our ability to understand and use lanthanide-doped luminescent nanoparticles.