Self-reduction and enhanced luminescence in transparent Mn2+-doped mullite glass-ceramics derived from EMT-type zeolite

Mn2+ activated glass-ceramic (GC) has received tremendous attention in the exploration of luminescent materials for solid-state lighting due to the high stability, broad red emission, and low toxicity. However, the doped Mn2+ ions still suffer from the oxidation and uncontrollable ions migration during the melting process of conventional preparation techniques, which is detrimental to the luminescence performance. Herein, transparent Mn2+-doped mullite GCs have been prepared at low temperature (similar to 850 degrees C) via the spark plasma sintering of EMT-type zeolite. The GC samples show typical red emission peaking at 620 nm that can be assigned to spin-forbidden T-4(1)(G)->(6)A(1)(S) transition of Mn2+ located in the octahedral coordination site of the host. Owing to the charge compensation mechanism and produced oxygen vacancies, the self-reduction of Mn3+ to Mn2+ ions is realized and the oxidization is inhibited. The mullite nanocrystals acted as additional scattering centers introduce Rayleigh scattering to enhance the emission intensity. Moreover, benefitted from the established mullite nanocrystals network, the Mn2+-doped GCs exhibit improved thermal conductivity up to 1.79 W K-1 m(-1) and more excellent mechanical properties than conventional GCs, simultaneously.