Tunable color emitting of CaAl2Si2O8: Eu, Tb phosphors for light emitting diodes based on energy transfer

► Both the emission of Eu2+ and Eu3+ were observed due to the self-reduction effect. ► Energy transfer from Eu2+ and Tb3+ in CaAl2Si2O8 were elucidated. ► The modulation of valence distribution of Eu2+/Eu3+ were discussed in detail. ► White emission can be obtained by controlling the codoped contents of Li+.