Rapid microwave preparation of cerium-substituted sodium yttrium silicate phosphors for solid state white lighting

Abstract

The preparation of two cerium-substituted sodium yttrium silicate phosphors, NaY9Si6O26:Ce3+ and Na3YSi2O7:Ce3+, was achieved using rapid heating via a modified microwave-assisted preparation technique. Activated carbon is used as a microwave susceptor allowing reaction temperatures greater than 1000 °C to be reached in minutes while producing the reducing atmosphere necessary to achieve Ce3+. Because this method immediately heats the sample and does not employ a H2/N2 gas mixture to maintain Ce3+ in its reduced state, volatilization of starting materials is limited, allowing the products to be prepared from a stoichiometric mixture of starting materials. The samples prepared were characterized using synchrotron X-ray powder diffraction and fluorescence spectroscopy. Photoluminescence measurements indicate NaY9Si6O26:Ce3+ contains a broad excitation band in the UV ranging between 280 nm and 330 nm that produces a blue emission between 350 nm and 500 nm with a 10% quantum yield. Na3YSi2O7:Ce3+ has a strong absorption band at 350 nm and also emits in the blue (375 nm–500 nm) with a quantum yield of 28%.