Visible-emitting hybrid sol-gel materials comprising lanthanide ions: Thin film behaviour and potential use as phosphors for solid-state lighting

The synthesis and characterization, as well as the film-forming and luminescent properties of four visible-emitting hybrid organic-inorganic sol-gel materials are reported. They show thermal stability up to 165 °C. Deposition conditions were optimized to coat these materials as homogeneous and transparent thin films (∼50 nm) of a smooth surface, as probed by AFM. They were specifically designed to emit the three primary colours. The blue-emitting material 1 was made up of a polyfluorene derivative embedded into a silica matrix, while the green (2) and red (3)-emissive materials comprise the Tb^III and Eu^III ions bound to the matrix, respectively. The films showed relatively high emission quantum yield efficiencies, with values of 19% (blue), 46% (green), and 21% (red). The three emitters were used to design a single emissive material (4) that showed emission from yellow-green to blue in a wide range of excitation wavelengths (254-380 nm). In particular, white light was obtained for excitation at 340 nm. The Eu^III material was investigated as a potential phosphor coated on an UV LED, and primary investigations on its stability under operating conditions are reported.