Luminescence properties of Ho3+ co-doped SrAl2O4:Eu2+, Dy3+ long-persistent phosphors synthesized with a solid-state method

In this study our aim was partially substituting or replacing Dy3+ co-dopant ions in SrAl2O4:Eu2+, Dy3+ phosphors with less expensive Ho3+ co-dopant ions in order to open a more economical way towards the industrial scale synthesis of long-persistent strontium-aluminate phosphors while maintaining the good optical properties of Dy3+ co-doped phosphors. This was achieved by finding the optimum ratio between the Dy3+ and Ho3+ co-dopants to get the highest initial intensity and by compensating the fast decay speed caused by Ho3+ co-doping via defect site generation in the host through non-stochiometric Sr/Al ratios.The initial emission intensity was the highest when the co-activator was substituted entirely with Ho3+ ions, and even the phosphors containing mixed co-activators featured higher initial emission intensities than the reference Dy3+ co-doped samples. However, the samples co-activated with Ho3+ or mixed co-activators exhibited faster decay speeds relative to the Dy3+ co-activated samples. This negative effect could be compensated by increasing the relative amount of aluminum in the phosphor.