PERSIST

Project summary: In persistent luminescence materials, energy can be stored by controlled traps/defects under brief irradiation -namely few minutes under UV or natural daylight-. This energy is then released at room temperature for several hours via light emission once the excitation is stopped. The search for innovative and properties-enhanced materials is an active research -mainly in Asia- and has recently led to several new phosphor materials and new applications (such as bio-imaging at the nanoscale). Most of these researches were performed on powder materials. A better understanding of the persistent luminescence mechanism is crucial for the development of practical applications. Moreover, the quest to unravel the mechanism behind the persistent luminescence has entered a new path. In the PERSIST project three complementary research groups (IRCP-Paris, CEMHTI-Orleans and IMN Nantes) and one company (BREVALOR-Swiss) are gathered to propose some breakthroughs in the field. The purpose of the PERSIST project is twofold. (i) In one part for better adaptation to new lighting requirements, we aim at overtaking the current persistent luminescence properties. For instance by developing cationic substitutions in the hexagonal polymorph of the commercial monoclinic SrAl2O4. Indeed under 460 nm blue LED excitation, the hexagonal polymorph and related compounds obtained with cationic substitutions are expected to glow longer times that the commercial monoclinic. This is expected from the persistent luminescence excitation recently obtained. Furthermore cationic substitutions can also tune the color from blue or green to white. Scientific deep analysis of the trapping and recombination centers will be characterized by combining state of the art of experimental optical and magnetic techniques available in the three research laboratories and band structure calculations. (ii) The second main objective of the PERSIST project relies on the huge “volume effect” expected from the transparent persistent phosphors to be developed. If only a few micrometers from the phosphor surface are participating to persistent luminescence in powder samples, using transparent or translucent materials will open the path to much enhanced capabilities. PERSIST project will be focused on transparent glass-ceramics with an original way, recently proposed, to obtain crystals embedded in glass, ceramics and single crystals, starting at first by strontium aluminate and relative compounds where first results were recently obtained. Preliminary centimetric large crystals, not optimized, of calcium aluminate were grown for the first time. Other materials will be grown by the Czochralski processes within the project such as garnet spinels and mixed-aluminates. Within these new materials, charge and discharge capabilities will be tested for indoor and outdoor applications. If the applications at the present time for such materials mostly consist in emergency signalization, dials, displays and medical diagnostics, stronger signal and new designs could open the path to new “outdoor” applications (in building materials, road signs). Finally, it is anticipated that the important enhancement of persistent luminescence expected from transparent materials will also be interesting for new applications in luxury and jewelry.