Principle of luminescence upconversion and its enhancement in nanosystems

Most emissions are down conversion (DC) in nature, which means that the emission energy is lower than the excitation energy. In this book, we introduce an opposite concept-upconversion (UC) emission-the emission of one higher energy photon upon the excitation of several lower energy photons. The latter is very attractive for applications in data storage, multicolor displays, photovoltaic devices, biological eld, etc. In recent years, the development of nanotechnology has been increasingly inviting scientic interest, especially the interest of the biomedical eld, in relevant material systems such as lanthanide (Ln) ions doped materials. In these materials, near-infrared (NIR) photons are converted to higher energy photons ranging from ultraviolet (UV) to NIR. Here, the excitation wavelengths are especially