Photoluminescence enhancement in manganese-doped magnesium stannate phosphors synthesized by millimeter-wave irradiation

We have investigated photoluminescence (PL) of Mg₂SnO₄:Mn phosphors synthesized by the irradiation with millimeter-wave of 24 GHz. The PL spectrum at room temperature is dominated by a green band peaking at 500 nm, suggesting the existence of tetrahedral Mn²⁺ sites. When the phosphors are grown by the millimeter-wave heating, the 500 nm band is so much intense compared to those by the electric furnace heating. To clarify the origin of the PL enhancement, we have carried out the measurements of scanning electron microscope (SEM) and electron spin resonance (ESR). The SEM image exhibits the growth of small round particles with an average size of 1.6 μm. Such well-grown micron-sized particles were not observed under the electric furnace heating. The ESR spectra exhibit six prominent lines, the intensity of which becomes greater for the phosphors obtained by the millimeter-wave heating. From this observation, it is supposed that the PL enhancement is mainly due to the increase in the number of tetrahedral Mn²⁺ sites. Therefore, the millimeter-wave heating has an important advantage over the electric furnace heating in the synthesis of Mg₂SnO₄:Mn phosphors.