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...

As microelectronic Power Devices increase their performances, there is a need to implement low thermal budget annealing processes on thin silicon wafers, typically few tenth of micron thick. To enhance the performance of these devices, particularly for Insulated Gate Bipolar Transistor (IGBT), there is a need to activate two different layers of doped silicon at different depth from the backside of the wafers, one P-doped and another N-doped (buffer layer). These annealing processes have to be able to localize a high temperature heat front limited to a very thin layer not to damage the other side of the wafer, where metallic structures would not allow temperature above 400°C. In this work, we annealed wafers implanted with Boron and Phosphorous with Excico Long Pulse Exciplex laser (308nm excimer laser, 180ns pulse) to induce two different silicon phases where both a liquid and a solid phase process activate the 2 different dopant layers. SIMS and SRP measurements were performed to quantify the amount of dopant activated during the laser annealing. The rate of defects in the silicon was measured by RBS. Depending on the laser energy density and implantation conditions, we were able to identify a process window within we achieve a high activation rate of Boron in the melting phase and of the Phosphorus in the solid phase.