Controlling energy transfer between multiple dopants within a single nanoparticle

Abstract

Complex core-shell architectures are implemented within LaF3 nanoparticles to allow for a tailored degree of energy transfer (ET) between different rare earth dopants. By constraining specific dopants to individual shells, their relative distance to one another can be carefully controlled. Core-shell LaF 3 nanoparticles doped with Tb 3؉ and Eu 3؉ and consisting of up to four layers were synthesized with an outer diameter of Ϸ10 nm. It is found that by varying the thicknesses of an undoped layer between a Tb 3؉ -doped layer and a Eu 3؉ -doped layer, the degree of ET can be engineered to allow for zero, partial, or total ET from a donor ion to an acceptor ion. More specifically, the ratio of the intensities of the 541-nm Tb 3؉ and 590 nm Eu 3؉ peaks was tailored from <0.2 to Ϸ2.4 without changing the overall composition of the particles but only by changing the internal structure. Further, the emission spectrum of a blend of singly doped nanoparticles is shown to be equivalent to the spectra of co-doped particles when a core-shell configuration that restricts ET is used. Beyond simply controlling ET, which can be limiting when designing materials for optical applications, this approach can be used to obtain truly engineered spectral features from nanoparticles and composites made from them. Further, it allows for a single excitation source to yield multiple discrete emissions from numerous lanthanide dopants that heretofore would have been quenched in a more conventional active optical material.core-shell ͉ rare earth T he past 10 years have witnessed an increase in research on rare earth-doped nanoparticles (NP) because of the numerous applications to which they may be applied. The rare earth ions, typically trivalent, although sometimes di-or tetravalent, can exhibit luminescent emissions ranging from 172 nm to Ͼ7 m providing that they are doped into a host of high intrinsic transparency and low vibrational energy. Because of such a broad spectral range of potential emissions, active NPs are being considered for practical use in LEDs (1), solar cell energy conversion (2, 3), lasers and amplifiers (4), and biological assaying (5, 6).Heavy metal halide crystals are known to be excellent host materials for rare earth ions because of their intrinsically low phonon energies. Unfortunately, they also tend to be hygroscopic, brittle, and not thermally robust. One solution to this problem was found in the development of glass-ceramics, where halide nanocrystallites are nucleated in an oxide glass matrix. Some of the optically active rare earth (RE) ions partition into the crystallites and emit from lower vibrational energy host nanocrystals with improved quantum efficiencies than if they were emitting from the oxide host matrix (7). For example, LaF 3 nanocrystals were precipitated from oxyfluoride compositions by Dejneka (8) to create glasses that were more easily processed than fluoride glasses while maintaining their superior optical properties over oxide glasses (8). While this approach is beneficial for improving t...

Preparation and Characterization of Rare Earth Doped Fluoride Nanoparticles

“…In terms of halides core/shell nanoparticles, to date investigations have focused mostly on the lanthanide fluorides [10,29,30,31,32,36,37,38,39]. Core/shell synthesis can be divided in two groups.…”

Recent advances in energy transfer in bulk and nanoscale luminescent materials: from spectroscopy to applications

“…Similar to their bulk counterparts the ET transfer has been intensively examined at the nanoscale in various RE and TM activated systems. [135][136][137] The core-shell structure therefore can be employed to manipulate spectral features for multi-ion activated materials by modulating the interaction between ions in the nanostructure. Since the critical distance for ET is in the order of several nanometers, the size of the nanostructure might be a new parameter for the control of ET in confined space.…”

Ultra-broadband amplification through nanotechnology

“…Alternatively, a core-shell structure can be used (Figure 1b) whereby energy transfer among active RE ions is controlled to allow the active ions to transfer a portion of their energy to other active ions. 6 In this way, a single particle can have multiple emissions without having to segregate the different RE to separate particles but only to different shells within a nanoparticle. (b) Complex core-shell structure for controlling energy transfer between RE ions.…”

“…It has been shown in previous work that the use of nanoparticles to constrain rare earth to separate regions of a nanocomposite results in no energy transfer between rare earth ions. 6 In this way, any rare earth doped nanoparticle can be made and placed into a fiber amplifier nanocomposite. …”