Elias H. Penilla
and Engineering Program
University of California, Riverside
Processing and Consolidation of Bulk Transparent Polycrystalline Ceramics: New Avenues for Photonic Waveguides and Photoluminescent Gain Media
Location: EB1 Room 1011
Friday, April 1st 2016 - 11:00 am
The study of transparent ceramics has significantly rebounded in the past decade as higher quality materials have been achieved with improved sintering/consolidation techniques. The densities and consequently, the transparencies of sintered bodies often rival their single-crystal counterparts. Typically, single crystal and polycrystalline ceramic host materials are synthesized, doped, and grown/consolidated with transition metals and rare-earths (RE) using equilibrium processing techniques (Czochralski, sintering, hot-pressing etc.). While largely developed, these techniques have limitations. For example producing transparent, non-cubic ceramics with grain sizes that mitigate birefringence has largely been elusive with traditional techniques. Additionally, RE-doping of alumina to levels requisite for PL purposes is impossible with equilibrium techniques because the equilibrium RE-solubility is too low (~10-4%). Conversely, little attention has been given to producing RE-doped bulk transparent ceramics with non-equilibrium processing techniques. Here we report on the application of the Current Activated Pressure Assisted Densification (CAPAD) technique for producing functional transparent oxide ceramics such as RE-doped alumina, with grain sizes that mitigate birefringence and with rare-earth dopant concentrations as high as 0.5 at%, orders of magnitude higher than previously reported, highlighting the technique's advantage to access new chemical phases that can be used as solid-state optically pumped laser gain media. The application of CAPAD for the production of cubic symmetry transparent ceramics will also be discussed. The role of point defects on the linear and non-linear optical properties will be addressed, and specifically we will show examples of how the oxygen vacancy concentration can be used to develop devices such as linear waveguides in the bulk polycrystalline ceramics. A common theme of this talk will be the interplay between material processing, the resultant material properties, and the development of optical devices using transparent polycrystalline ceramics.