Effect of extra added Mg2+ and Si4+ on the microstructure and luminescence properties of Ce:YAG ceramic phosphors for high power LED/LD lighting. Issue 7 (1st April 2023) - Zhang, Qian
Abstract: The study deals with the use of different amounts of MgO or tetraethyl orthosilicate (C8 H20 O4 Si, TEOS), from 0.04 wt %, 0.06 wt %, 0.08 wt %, 0.4 wt %, 0.6 wt % to 0.8 wt %, respectively, as additional sintering aids during the vacuum sintering of transparent Ce 3+ doped Y3 Al5 O12 (Ce:YAG) ceramics to investigate their effect on microstructure and luminescence properties. A comparative study was carried out by using X - ray diffraction, scanning electron microscopy/energy dispersive X - ray spectroscopy, optical and photo-luminesce spectra, as well as electroluminescent spectra. The dominant garnet phase was obtained even when adding 0.8 wt % of MgO or TEOS, while adding MgO led to finer average grain size (∼ 5 - 10 μm) and more homogenous distribution compared to TEOS (∼ 20 - 25 μm) in Ce:YAG ceramics. Adding a large amount of MgO was found to result in the segregation of MgO in Ce:YAG ceramics, while an excess of TEOS led to the segregation of Al2 O3 . A strong absorption peak at 308 nm was observed in Ce:YAG ceramics with MgO sintering aids, which was ascribed to the existence of Ce 4+ induced by a charge compensation effect of Mg 2+ . The optimum transmittance reached 80% @ 800 nm in Ce:YAG ceramics when adding 0.6 wt % TEOS, which also exhibited a maximum luminous efficacy of 106 lm/W. Si 4+ was experimentally proved to have a better optimization effect on luminous efficacy compared to Mg 2+ . Highlights: MgO or TEOS (C8 H20 O4 Si) was added as additional sintering aids in a wide amount range. MgO proves to have distinct inhibit effect on the grain growth. Better luminous efficacy were observed in ceramics with TEOS additives.