Photoluminescence upconversion in monolayer WSe2 activated by plasmonic cavities through resonant excitation of dark excitons oleh Niclas S. Mueller, Rakesh Arul, Gyeongwon Kang, Ashley P. Saunders, Amalya C. Johnson, Ana Sánchez-Iglesias, Shu Hu, Lukas A. Jakob, Jonathan Bar-David, Bart de Nijs, Luis M. Liz-Marzán, Fang Liu, Jeremy J. Baumberg