1. Photophysics Group, Centre for Molecular Nanometrology,
Department of Physics, SUPA, University of Strathclyde, John Anderson Building, 107 Rottenrow, Glasgow G4 0NG, U.K.
2. Thin Film Centre,
SUPA, University of the West of Scotland, Ayr KA8 0SX, U.K.
3. Department of Physics, Beihang University, Beijing 100191, China
4. Centre
for Molecular Nanometrology, WestCHEM, Department of Pure and Applied
Chemistry, University of Strathclyde, Glasgow G1 1XL, U.K.