Supporting Information Distinct mechanisms for the upconversion of NaYF 4 :Yb 3+ ,Er 3+ nanoparticles revealed by stimulated emission depletion Kyujin Shin, Taeyoung Jung, Eunsang Lee Gibok Lee, Yeongchang Goh, Junseok Heo, Minhyuk Jung, Eun-Jung Jo, Hohjai Lee, Min-Gon Kim, and Kang Taek Lee * Department of Chemistry, School of Physics and Chemistry, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, Korea Corresponding Author ktlee@gist.ac.kr Equally contributed authors. Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics. This journal is © the Owner Societies 2017