The University of Innsbruck has succeeded in developing a new red phosphor that increases the luminous efficacy of LEDs and makes lighting much more efficient.
Light-emitting diodes or LEDs can only produce light of a certain colour. The situation is different with white light, which consists of several colours and requires a special colour mixing process. With white LEDs, red and yellow-green phosphors are stimulated by the light of a blue diode. The particles emit corresponding light in the red and green range and, in combination with the blue light, produce white light, explains Hubert Huppertz from the Institute for General, Inorganic and Theoretical Chemistry at the University of Innsbruck.
The weakness of conventional white LEDs lies in their low luminous efficacy. This is due to the nature of the human eye. It perceives green particularly well, blue and red less well. Huppertz and his team have now succeeded in developing a new red phosphor whose light is well perceived by the eye. The phosphor increases the luminous efficacy of white LEDs by around one-sixth and significantly improves the energy efficiency of lighting systems. The innovation is based on red phosphorus, which meets all the requirements for the optical properties of a phosphor. Based on the formula Sr[Li2Al2O2N2]: Eu2+, the researchers named it SALON.
The development goes back to Huppertz’s doctorate, which he completed at the University of Bayreuth. At that time, he developed nitrides doped with europium, which fluoresce. Europium is a rare earth metal. Further optimised by the former research group, the fluorescent nitrides are now widely used.
The red colorants of red phosphorus are partly responsible for the fact that LEDs no longer glow cold white, but warm white as well. But even these red dyes are not clearly perceptible to the human eye. Although they emit red light in the visible range, a large part of the energy goes into the infrared range, which the human eye does not perceive.
With the newly developed SALON phosphor, it has now been possible to slightly shift the light emission from red towards blue in order to obtain an orange-emitting substance. Hubert Huppertz:
“With SALON we have less energy loss, it emits exactly in the red area we can see.”
It was difficult to optimise the synthesis, the research team reports. Initially, only a few very small particles were available in an inhomogeneous sample. Finally, it was possible to isolate a crystal from one of the most promising synthesis products and thus determine the structure of the new material.
To further characterize the new material, the researchers cooperated with industrial partner OSRAM Opto Semiconductors, the Fraunhofer Institute for Microstructure of Materials and Systems IMWS as well as the research group led by Dirk Johrendt at the Ludwig Maximilian University in Munich. The innovation has already been registered for a patent.
Click here for the paper:
Sr[Li2Al2O2N2]: Eu2+ – A high-performance red phosphor to brighten the future. Gregor J. Hoerder, Markus Seibald, Dominik Baumann, Thorsten Schröder, Simon Peschke, Philipp C. Schmid, Tobias Tyborski, Philipp Pust, Ion Stoll, Michael Bergler, Christian Patzig, Stephan Reißaus, Michael Krause, Lutz Berthold, Thomas Höche, Dirk Johrendt & Hubert Huppertz. Nature Communications 10, 1824 (2019)