1. Department of Chemistry, Winston-Salem State University, Winston-Salem, North Carolina 27110, USA
2. División de Ciencias e Ingenierías, Universidad de Guanajuato-Campus León, León, Guanajuato 37150, Mexico
3. Molecular and Biophotonics Group, Applied Physics Division, Physical Measurement Laboratory, National Institute of Standards and Technology, Boulder, Colorado 80305, USA