1. Solid
State Lighting and Energy Center, University of California, Santa Barbara, California 93106, United States
2. Materials
Department, University of California, Santa Barbara, California 93106, United States
3. Department
of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, United States
4. Merck
KGaA, Frankfurter Strasse
250, 64293 Darmstadt, Germany