1. Photonics and Energy Research Laboratory, University of Texas Rio Grande Valley, Edinburg, Texas 78539, United States
2. Center for Nanotechnology, Department of Mechanical Engineering, University of Texas Rio Grande Valley, Edinburg, Texas 78539, United States
3. Department of Chemistry, University of Texas Rio Grande Valley, Edinburg, Texas 78539, United States
4. Department of Physics and Astronomy, University of Texas Rio Grande Valley, Brownsville, Texas 78520, United States