| AVS 57th International Symposium & Exhibition | |
| Energy Frontiers Topical Conference | Thursday Sessions |
| Session EN+NS-ThM |
| Session: | Nanostructures for Energy Conversion & Storage II |
| Presenter: | V.D. Jankovic, UCLA |
| Authors: | V.D. Jankovic, UCLA J. Hoang, UCLA J.P. Chang, UCLA |
| Correspondent: | Click to Email |
Rare-earth (RE) oxides represent an important class of photonic materials owing to their nonlinear optical and upconversion (UC) properties which find applications in high power lasers, remote sensing, optical communications and photovoltaics. In the context of solar cells, these materials could increase cell efficiencies by upconverting photons with energies below and near the silicon bandgap (1.1eV) which are poorly absorbed by the indirect band-gap semiconductor to higher energy photons that can be absorbed more efficiently. Unfortunately, up-conversion efficiencies in rare-earth ions are usually low due to non-radiative processes such as concentration quenching. One strategy to address this problem is to couple RE ions with metal nanoparticles. Noble metal nanoparticles exhibit localized surface plasmon resonances which can readily be tuned to a particular spectral range of interest by means of size, shape and local dielectric environment. By coupling metal nanoparticles’ plasmon resonances to rare earth ion energy transitions, the absorption cross sections of rare earth ions can be significantly improved.
In this work, we designed and synthesized Au|Yb:Er:Y2O3 core|shell nanorods as a potential route to improve solar cell efficiencies in the near infrared regime. A modified Mie scattering algorithm determined the optimum theoretical Au nanorod aspect ratio to be 9, for a resonance close to the Yb 980-nm energy transition. The Au nanorods were synthesized using a surfactant mediated growth technique, in which cetyltrimethylammoniumbromide micelles were used to direct the growth of Au nanoparticles in the [111] direction while suppressing the growth in [100] and [110] directions. Au nanorods with aspect ratios from 6 to 12 have been synthesized by varying the concentration of the reducing agent, ascorbic acid. Spatially and compositional controlled Yb:Er Y2O3 shells were deposited using sequential radical enhanced atomic layer deposition process. The plasmon-Er color center and plasmon-Yb sensitizer distance was systematically varied by controlling the thickness of the Y2O3 spacer layer from 1nm to 10nm. The length, aspect ratio, nanorod monodispersity and shell thickness were verified using transmission electron microscopy, while the shell composition was verified by energy dispersive X-Ray spectroscopy. Photoluminescence and radiative lifetime measurements with 980 nm excitation were used to investigate the distance dependence effects of the noble metal-emitter coupling on the optical properties of the core|shell nanorods. Quantitative measurements of the absorption cross section are underway and will also be presented