A simple process for preparing light-emitting layers of silica with wide colour variation has been developed by Italian scientists.

The promise of preparing white light emitting materials for flat displays stimulated a team led by Gianluca Accorsi of National Research Council, Bologna, to develop luminescent hybrid layers. They combined the light emission properties of different lanthanide-based dyes with stable and optically transparent glassy films.

Lanthanide luminescence has major obstacles to overcome before it can realise its potential for many applications, including photonics. The obstacles include low light absorption and losing luminescence intensity due to interactions between the long-lived lanthanide excited states and the hosting matrix.

Accorsi's team have overcome these hurdles by employing acetophenone units to play the role of antennae and using a transparent silica layer as the host matrix, preventing excited state deactivation. Furthermore, these highly efficient lanthanide complexes are covalently linked to (rather than dispersed in) the matrix, allowing homogeneous loading of controlled distrubutions of the well-known red Eu(III) and green Tb(III) emitters.

Accorsi said that an advantage of their synthetic strategy is that it is based on the 'statistical distribution of the different photoactive centres within the transparent film, and not on the tedious and time-consuming multistrata arrangement technique often used, as an example, in the fabrication of white-light emitting OLED devices.' He went on to forecast 'The use of blue-greenish emitters could afford white-light emitting single layers obtained through the easily manageable synthesis of photoactive materials and simple fabrication processes.'

This view was echoed by Vincenzo Balzani, a specialist in photochemistry and nanotechnology at the University of Bologna, Italy, who believes that this 'most interesting result may open the way to construct colour tunable luminescent devices'.

Ian Gray