| AVS 58th Annual International Symposium and Exhibition | |
| Nanometer-scale Science and Technology Division | Monday Sessions |
| Session NS-MoA |
| Session: | Frontiers in Nanophotonics and Plasmonics |
| Presenter: | Vladan Jankovic, University of California Los Angeles |
| Authors: | V. Jankovic, University of California Los Angeles J.P. Chang, University of California Los Angeles |
| Correspondent: | Click to Email |
The conversion of electromagnetic (EM) energy from free propagating radiation to localized energy and vice versa in the radio frequency (RF) and microwave domains is accomplished with the use of antennas. Optical antennas are analogous to their RF and microwave counterparts, but there are crucial differences in their physical properties and scaling behavior because metal is a highly dispersive material with finite conductivity at optical frequencies. Optical antennas are not driven by galvanic transmission lines like RF antennas, instead, localized oscillators such as atomic emitters are brought close to the feed point of the antennas, and electronic oscillations are driven capacitatively.
In this work, Au nanoparticles of different shapes (spheres, rods and stars) were used as antenna elements, Er3+ ions in an Y2O3 host matrix were used as atomic emitter antenna driving elements while the capacitative gap between the antenna element and the atomic emitter was controlled by deposition of an ultra-thin SiO2 inner shell between the Au nanoparticle and the Yb:Er:Y2O3 outer shell. A 4-5nm silica spacer layer was deposited through a controlled TEOS hydrolyzation reaction and was shown to be effective in preventing quenching yet enabling energy coupling between the Au nanorod and the RE-ion doped oxides. Spatially and compositionally controlled Yb:Er:Y2O3 outer shells were deposited using both wet chemistry methods and radical enhanced atomic layer deposition (RE-ALD).
Upconversion (UC) spectral, power dependence and radiative lifetime measurements with 532nm, 750nm 980 nm and 1064nm laser excitation were used to assess the coupling of the Au optical antenna to the emitter ions as a function of antenna shape, spacer layer thickness and spectral and spatial mode overlap efficiency. Preliminary optical characterization showed a 2X earlier onset of upconversion with 980nm excitation for Yb:Er:Y2O3 coupled to an Au nanorod antenna compared to pure (uncoupled) Yb:Er:Y2O3 nanoparticles. Power dependence measurements with 980nm excitation showed a >5 slope indicating a multi-photon absorption induced luminescence process for the Au-coupled erbium and a <2 slope for the uncoupled erbium, indicating a two photon absorption (expected for erbium with 980nm excitation). These optical antenna core|shell particles have potential application in bio-imaging and light trapping for solar and sensor applications.