Luminescent Lanthanide Sensors and Lanthanide Doped Upconversion Nanoparticles: Current Status and Future Expectations

Abstract

Lanthanide ions exhibit fascinating optical properties with their potential applications largely governed by their interaction with light. This chapter deals with some relevant aspects concerning the electronic and coordination properties of lanthanides and the basic principles related to the design of efficient luminescent lanthanide complexes. The cleverly designed environment consisting of ligands containing adequate chromophoric groups provide a rigid and protective coordination shell to minimize non-radiative deactivation. Lanthanide doped upconversion nanoparticles (UCNPs) have attracted extensive attention in the field of biomedical applications due to their long luminescence lifetime, narrow emission bandwidth, high quantum yields and low toxicity. In this chapter the upconversion phenomenon is explained with emphasis on the mechanism of upconversion, selection of host materials and impurities in host matrices. The various chemical approaches for the synthesis of lanthanide doped UCNPs have also been discussed. Subsequently, some selected results of our recent work concerning the photoluminescence studies of Eu(III) and Yb (III) complexes are reported which exhibit the characteristic emission bands of Eu(III) ion corresponding to 5Do → 7FJ (J = 0–4) transitions with intense red emission at 615 nm due to 5D0 → 7F2 transition of the central Eu(III) ion. These complexes show long radiative lifetime and quantum efficiency which suggest that these complexes can be well utilized as fluorescent probes.