Self-reduction process and enhanced blue emission in SrAl₂Si₂O₈: Eu, Tb via electron transfer from Tb³⁺ to Eu³⁺

Eu, Tb co-doped SrAl₂Si₂O₈ luminescent materials were synthesized via a high-temperature solid-state reaction. Excitation spectra of SrAl₂Si₂O₈: Eu²⁺ gives two broad excitation bands maximizing at 270 and 330 nm, resulting from splitting Eu²⁺ energy levels in octahedral crystal field. Eu single doped SrAl₂Si₂O₈ luminescent material exhibits two emission bands at about 406 and 616 nm. Intensity of the blue emission from Eu²⁺ is always strong, compared with that of the red emission band of Eu³⁺. Reduction from Eu³⁺ to Eu²⁺ can be explained with the model of charge compensation. Blue emission in SrAl₂Si₂O₈: xEu was strengthened after incorporation of Tb, which can be explained by electron transfer from Tb³⁺ to Eu³⁺ (Tb³⁺+Eu³⁺ → Tb⁴⁺ +Eu²⁺). Under 230 nm excitation, intensity of Tb³⁺ emission was nearly unchanged and that of Eu²⁺ was increased, obviously due to the delivery of more electrons to Eu³⁺. The strongest emission of Eu²⁺ in 0.09Eu/0.06Tb co-doped SrAl₂Si₂O₈ and excited at 270 and 330 nm was remarkably enhanced by about four times compared to that of 0.15Eu Single doped SrAl₂Si₂O₈. All of the results indicate that SrAl₂Si₂O₈: xEu, yTb are potential blue emitting luminescent materials for UV-LEDs. More importantly, this research may provide a new perspective in designing broad band blue luminescent materials.