FellowMohamed Radwan
Project NameTransparent Luminescent Oxynitrides
Host organisationInstitute of Inorganic Chemistry
Duration of the project11.01.2016 - 31.12.2018

Abstract
The European Union member states took measures in recent years to phase-out incandescent bulbs and switch to energy-saving lighting sources. White light-emitting diodes (wLEDs) are solid-state mercury-free lighting technologies widely penetrated in liquid crystals displays (LCDs) backlighting in televisions, computers, mobiles and smart devices which are remarkable in our daily life. For small-area lighting, wLEDs have higher light efficiency and longer lifetime than other traditional sources such as incandescent, compact fluorescent and halogen lamps. However, their progress in large-area lighting is slow mainly due to the need to improve the light intensity and thermal conductivity management of phosphor materials. The current project aims to develop nanostructured transparent luminescent oxynitride ceramics at a low cost in order to obtain phosphor materials with high luminescence efficiency for high-energy wLEDs. The project focuses on the following research objectives: 1) Chemical synthesis of nano-size phosphor powders with oxynitride compositions of MAlON (M = alkaline earth or transition metals) and Si2-xAlxO1+xN2-x by using the co-precipitation and polymer-pyrolysis routes. 2) Sintering of synthesized phosphor powders by rapid hot pressing (RHP) and/or hot isostatic pressing (HIP) to prepare fully dense transparent phosphor ceramics of uniform nano-scale microstructure. 3) Evaluation of the powder and bulk phosphors in terms of phase composition, particle morphology, photoluminescence properties, optical transmittance, thermal conductivity, thermal expansion and mechanical properties. The project results are expected to be a one step forward for the development of large-area SSL which will significantly decrease the energy consumption for lighting in Europe.

Project Summary with Interim Results

Transparent Luminescent Oxynitrides (acron. LUMON) is a research project within the Third Call of the Incoming Mobility Scheme at the Slovak Academy of Sciences Programme (SASPRO) co-funded by the Slovak Academy of Sciences (SAS) and the Marie Curie Actions of EU 7th Framework Programme (EU-FP7). The project is implemented at the Institute of Inorganic Chemistry (IIC SAS) in Bratislava and funded for 3 years starting from January 2016.

The LUMON project aims to conduct basic research studies to develop new transparent luminescent ceramics as remote phosphors for the application of high-power white light emitting diodes (wLEDs). It focuses on the preparation of doped transparent magnesium aluminium oxynitride (MgAlON) and silicon oxynitride (Si2N2O) ceramics, in addition to the characterization of their structural, thermal and optical properties.

In the first year (11.01.2016 – 31.12.2016), the objectives of the project were to prepare doped MgAlON ceramic powders by appropriate chemical methods, and to analyse their physicochemical properties.

MgAlON ceramics are non-stoichiometric solid-solutions in the ternary MgO-Al2O3-AlN system that form at a temperature ≥ 1750 °C and remain stable at room temperature. They constitute homogeneous single-phase region of cubic spinel crystal structure, and are characterized by high-temperature chemical stability and promising optical transparency in the visible–infrared range of the spectrum.

During the last 12 months of the project, pure MgAlON spinel powders have been synthesized with 3 different compositions from the mixtures of MgO, Al2O3 and AlN powders by the solid-state reaction method. Additionally, different sintering routes were investigated to fabricate transparent MgAlON ceramics to understand the effect of composition of MgAlON spinels on optical transmittance. Recently, full-dense semi-transparent MgAlON material was prepared by combination of reactive pre-sintering in vacuum and post hot isostatic pressing (HIP).

It is expected in the second year of the project to (1) improve the optical transmittance of the sintered MgAlON specimens, (2) get more knowledge about the relationship between the composition of MgAlON and optical transmittance, (3) fabricate doped transparent phosphor plates based on favourable MgAlON compositions, and (4) evaluate the outcomes of photoluminescence properties. Most likely, with the currently developed two-steps synthesis and sintering methodology, the preparation of transparent Si2N2O-based phosphors will begin later in the second half of the year.