(213a) Engineering Optical Properties by Controlling the Concentration and Proximity of Rare Earth Dopants in Y2O3 Using Radical Enhanced ALD

The realization of compact fiber optic networks is limited by the control of the dopant ion's identity and its distribution. Each rare earth (RE) ion contains spectral energy levels, whose transitions can be promoted by controlling the ion-ion proximity. In this work, a radical enhanced atomic layer deposition (RE-ALD) process, utilizing highly reactive radicals to activate surface reactions, is developed to design complex metal oxides with multiple dopants, whose concentration variation and spatial distribution control enable the synthesis of a wide range of multifunctional materials with tunable properties including magnetic, spectral, and electronic. Specifically, the control of dopant proximity and concentration is used to enhance desirable spectral transitions related to amplification at 1.54 micron for compact planar optical amplifier applications. Specifically, spatial distributions between Er³⁺ and various rare earth sensitizers (e.g. Yb and Eu) are investigated. The ability to control the spacing of each sensitizer allows for a unique study of the correlation between energy transfer and dopant proximity. Thin films of approximately 10 nm are synthesized by sequential radical-enhanced ALD of Y₂O₃, Er₂O₃, Yb₂O₃, and Eu₂O₃ at about 350^oC. The composition, microstructure, cation distribution, local chemical bonding and optical properties of the as-synthesized thin films were determined by x-ray photoelectron spectroscopy, electron microscopy and photoluminescence measurements. To optimize the effect of the sensitizer and minimize the concentration quenching, the concentration and spatial distance between Yb³⁺ and Eu³⁺ sensitizers and Er³⁺ were controlled by changing the global deposition cycle sequence. Extended x-ray absorption fine structure analysis verified the spatial control of dopants in the Y₂O₃ host. It was found that multi-dopant spatial control allows for incorporation of minimal active sensitization sites, allowing for the possibility of maximizing the active Er concentration while maintaining efficient energy transfer. This additional degree of control allows for a class of complex materials that can potentially outperform their conventional counterparts by many-folds in luminescence.