Novel red-emitting Sr6Al18Si2O37:Mn4+ phosphor for white LEDs

Mn4+-doped Sr6Al18Si2O37 phosphor is synthesized by a high temperature solid-state reaction method. Addition of H3BO3 flux leads to the formation of pure phase of Sr6Al18Si2O37, which is confirmed with XRD measurement. Sr6Al18Si2O37:Mn4+ phosphor can be effectively excited by both near-UV light (397 nm) and blue light (467 nm) of LED chips and emits a deep red emission at 665 nm due to the spin-forbidden E-2 ->(4)A(2) electron transition of Mn4+ ions. The optimized concentration of Mn4+ in the Sr6Al18Si2O37:Mn4+ phosphor is determined. Codoping a certain amount of Ge4+ ions improves the luminescence intensity of Sr6Al18Si2O37:Mn4+. The presence of Ge4+ leads to the formation of isolated luminescence center Mn 4 +/- ions rather than Mn4+-Mn4+ pairs connected with interstitial O2- and therefore eliminates the energy transfer, which enhances the Mn(4+)emission. All these results indicate that Sr6Al18Si2O37 could act as the host structure for Mn4+-doped phosphors.