Co-doping effect of Mn2+ on fluorescence thermostability of Ca-α-sialon:Eu2+ phosphors

Abstract

To reveal transition metal manganese ion (Mn²⁺) co-doping influence on Ca-α-sialon:Eu²⁺ phosphors, Mn²⁺ and europium ion (Eu²⁺) co-doped Ca-α-sialon phosphors were synthesized using a solid state reaction at 1600 °C under an ambient nitrogen atmosphere, and the effects of the co-dopant Mn²⁺ on the fluorescence thermostability of Ca-α-sialon:Eu²⁺ phosphors were systematically investigated. With increasing Mn²⁺ concentration, X-ray diffraction analysis shows a phase-pure host Ca-α-sialon structure and unit cell shrinkage (or a tighter structure). The photoluminescence spectra of all samples, with or without Mn²⁺ co-doping, exhibit a strong yellow emission. For the energy transfer between Mn²⁺ and Eu²⁺, the emission intensity is strongest when the co-doping concentration of Mn²⁺ is 0.02 molar and the CIE chromaticity index of the strongest emission composition is (0.474, 0.513) with a high internal quantum efficiency of 72.4%. Importantly, the fluorescence thermal quenching behavior of the as-prepared phosphors is remarkable and is over 80% of the initial emission intensity tested at room temperature, at a higher temperature of 275 °C. The major energy transition mechanism between co-dopants Mn²⁺ and Eu²⁺ during the heating process was deduced and considered to be a non-radiative energy transfer and phonon-assisted tunneling. Using further calculations, the thermal activation energy, ΔE, is 0.28 eV. In consequence, Mn²⁺ and Eu²⁺ co-doped Ca-α-sialon is an attractive and competitive phosphor candidate for applications in white light emitting diodes.