High Efficiency Emission of Eu²⁺ Located in Channel and Mg‐Site of Mg₂Al₄Si₅O₁₈ Cordierite and Its Potential as a Bi‐Functional Phosphor toward Optical Thermometer and White LED Application

Abstract Eu²⁺ activated Mg₂Al₄Si₅O₁₈ cordierite phosphor is prepared by sol gel synthesis. The reduction process is carried out in a vacuum atmosphere. X‐ray diffraction, luminescence, decay times, quantum yield and emission thermal stability are studied. The emission from Eu²⁺ ions at different lattice sites, such as magnesium vacancies and inside the interstate channels, are identified and discussed. Considerations on crystal field strength and bond length allow to assign the blue emission band peak at 445 nm to Eu²⁺ ions located inside the interstitial channel, while the red band centered at 615 nm is related to Eu²⁺ ions on Mg site. It is found that the Mg₂Al₄Si₅O₁₈:Eu²⁺ phosphor excited by UV shows broad emission from 375 to 700 nm with high quantum efficiency (60%). The emission of Eu²⁺ in Mg₂Al₄Si₅O₁₈ has very good thermal stability, at 100 °C the intensity reaches 97% relative to the emission measured at room temperature. The investigations show that cordierite can be used as a temperature sensor with relative sensitivity of 0.45% at 400 °C. Moreover, the fabricated light‐emitting diode composed of 365 nm near‐UV chip and Mg₂Al₄Si₅O₁₈:Eu²⁺ phosphor exhibits bright white light with CIE coordinates (0.32, 0.34) for correlated color temperature of 6282 K and color rendering index of 82.