1. Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, U.K.
2. Helio Display Materials Ltd., Wood Centre for Innovation, Oxford, OX3 8SB, U.K.
3. Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Singapore 138634, Singapore