Role of oxidative pre-calcination in extending blue emission of Sr4Al14O25 nanophosphors formed with microemulsions

► Conventional single step reductive calcination is improved by two stage calcination. ► Oxidative pre-calcination prevents formation of residual carbon and glassy phases. ► Allows improved incorporation of BO4 to form deep traps aiding persistence emission. ► Enhanced phosphorescence achieved with Sr3.95Eu0.01Dy0.04Al14O25:5-15 mol% H3BO3. ► Two stage process enhances long persistence with a lifetime of traps (τ3) of 850 s.