“…[16][17][18][19][20][21] The control of photon upconversion through core-shell nanostructures also advances the research in the new conceptual models like energy migration mediated upconversion (EMU) and interfacial energy transfer (IET) that greatly expands the observation of photon upconversion from more lanthanide ions (e.g., Eu 3+ , Tb 3+ , Dy 3+ , Sm 3+ , Ce 3+ and Nd 3+ ) and some transition metal ions (e.g., Mn 2+ ) apart from conventional ones (e.g., Er 3+ , Tm 3+ and Ho 3+ ). [22][23][24][25][26][27][28][29][30] So far, the upconversion emissions covering the ultraviolet (UV), visible (Vis) and near-infrared (NIR) spectral regions have been easily accessible, [31][32][33][34] consequently showing remarkable advantages in the fields ranging from biological imaging, therapeutics and neuroscience to nanophotonics. 17,[35][36][37][38][39][40][41][42][43][44][45][46] Among the various kinds of luminescent nanomaterials, multi-layer core-shell (MLCS) nanostructure UCNPs are a class of recently developed nanomaterials which have attracted special attention because of their much better flexibility and functionality with rational designs in size, composition, nanostructure and surface properties.…”