Low phonon-energy glass ceramics with tunable and ultra wide absorption and emission bands for highly efficient frequency conversion – GCWEB

This is a basic research project aiming at the development of innovative glass ceramics with very low phonon energy for highly efficient frequency conversion with tunable and ultra wide absorption and emission bands.
Materials for frequency conversion have been studied for decades and they are now used in many applications such as display and laser sources. More recently, these materials are intensively studied especially for general lighting based on LEDs and for increasing the efficiency of photovoltaic solar cells. All current materials suffer from the following problems: a). currently used materials are based on oxides with high phonon energy which is often detrimental for having high conversion efficiency. b). the absorption and emission wavelengths depend mainly on the nature of the active ions and they are not continuously adjustable to best fit the pumping wavelengths or to obtain the exact emission wavelength. c). All current materials are either glasses or crystals, without possibility to combine the advantages of these two states of solid materials.
This basic research project is to demonstrate the feasibility of active ions doped materials with large and tunable absorption and emission bands. We are not targeting any specific application. However, the materials to be developed can allow to better use the whole spectrum of the Sun for increasing the solar cell efficiency, to select the emission wavelength for obtaining desired CRI (color rendering index) for general lighting based on LEDs and to provide new laser sources with broadband emissions.
We propose to develop new luminescent materials, in bulk form and thin films, doped with divalent rare earths or/and transition metal ions. The originality and the novelty of this project are associated with
- the use of our newly developed and patented sulfide based glass ceramics for optical absorption and emission tuning in a wide range of wavelengths. These unique infrared transparent glass ceramics with highly controllable crystal content are characterized by very low phonon energy (lower than 300 cm-1 instead of 1100 cm-1 for silica glass).
- the use of a new concept of absorption and emission tuning of active ions (mainly divalent rare earth and transition metal) by creating different chemical environments for these ions in the same glass ceramic. In order to increase the tuning range, we will also combine the change of crystallinity with the change of composition in thin film structure. To the best of our knowledge, this concept is proposed for the 1st time. The crystallinity is referred as the crystal rate in a glass ceramic.
The success criteria of this project will be the following:
- Obtaining different doped bulk materials with wide absorption or emission bands of at least 200 nm (FWHM) in the UV/visible region and at least 300 nm (FWHM) in the near IR region. The peak absorption/emission wavelength should be tunable in a range of at least 100 nm
- Obtaining transparent thin film with at least 30% of crystals. The objective is to obtain 50% in order to take full profit of the benefic crystalline environment for active ions. The scattering losses should be very low, less than 2% at the wavelength of 1 µm for a thickness of 1 µm for example.
- Obtaining quantum efficiency higher than 100% for down conversion, the objective being to obtain 150%, and 30% for up conversion, the objective being to obtain 40%.

This is a multidisciplinary project including material synthesis, structure studies, thin film preparation and optical characterization.