Chapter 233 Spectroscopic properties of lanthanides in nanomaterials

Research and development of nanoscale luminescent materials are part of the rapidly advancing nanoscience and nanotechnology. This chapter provides an overview of recent studies on the energy level structures and excited state dynamics of lanthanide ions in nanostructures, such as lanthanide-doped dielectric nanocrystals; new nanophenomena and its consequences in electronic transitions, energy transfer, and phase transitions based on experimental and theoretical studies. The chapter discusses theoretical analysis of various mechanisms for luminescence enhancement (or quenching) and anomalous size and temperature-dependence. Lanthanides, specifically divalent europium, and many trivalent ions have the ability to emit light in near infrared (NIR), visible and near ultraviolet (UV) spectral ranges. Doping luminescent lanthanide ions into nanostructures is an ideal approach to developing nanophosphors for various applications. The chapter describes that in nanocrystals, the phonon density of states is no longer continuous, and most of the low-energy phonon (lattice vibration) modes are absent; therefore, the ion–phonon interaction is restricted. The luminescence decay time and efficiency of lanthanide ions in nanomaterials are also influenced by variation of local environments in addition to nanophenomena induced by confinement of the phonon density of states. Because of size confinement on electronic interactions and density of phonon states, nanostructured materials exhibit distinct optical, magnetic, and thermal properties in comparison with their bulk counterparts.