Application of Eu(III) activated tungstates in solid state lighting

Abstract

Tungstates play a major role in the, now for more than 60 years, ongoing scientific research of Eu(III) activated phosphors. Similarly, to other compounds featuring a closed shell transition metal anion like molybdates, vanadates, niobdates, tantalates, and tungstates are a family of materials that offer a wide range of potential host matrices for rare earth ions. Furthermore, tungstates provide several favourable characteristics like facile synthetic conditions via solid state synthesis, the possibility of high activator concentrations (low concentrations quenching), as well as intrinsic sensitization of lanthanides ions through a ligand-to-metal charge transfer (W⁶⁺/O²⁻). This review sets in by discussing the fundamentals of Eu(III) luminescence followed by a closer look at some general features of tungstates and their respective intrinsic luminescence. Various Eu(III) activated tungstates are explored in detail regarding their synthesis conditions and optical properties. Their compositional makeups and structures are correlated to the resulting optical properties. Potential strategies to improve the luminescent efficiency of new rare earth doped tungstates are derived from these correlations. In the closing section some general remarks regarding thermal quenching, concentration quenching, and charge transfer energies are discussed. Finally, comparisons to the related molybdates are drawn and the prospects of commercial application towards different fields of optical technologies are explored.