Achieving a Cr-free Cr-activated spinel phosphor by a one-step solid-state reaction

Cr 3+ -doped oxide phosphors attract increasing attention due to their tunable photoluminescence and versatile applications. Meanwhile, a hidden danger of toxic Cr 6+ -formation during the synthesis of Cr 3+ phosphors should also be emphasized. Herein, a co-doping strategy of Bi 3+ to a spinel-typed ZnAl 2 O 4 :Cr 3+ phosphor is performed and thoroughly suppresses the formation of Cr( vi ). As a result, an environmentally friendly Cr 6+ -free Cr 3+ -activated phosphor is successfully synthesized by a one-step solid-phase method in an air atmosphere. The mechanism of Cr( vi ) suppression is investigated. In the absence of the Cr( vi ) impurity, ZnAl 2 O 4 :Cr 3+ ,Bi 3+ shows an over doubled luminescence intensity than that of the pristine ZnAl 2 O 4 :Cr 3+ . This work offers an effective way to prevent Cr( vi ) pollution fundamentally for the production and application of Cr 3+ activated phosphors. Co-doping of Bi 3+ into the spinel ZnAl 2 O 4 reduces the density of anti-site defects and further inhibits the formation of the Cr( vi ) impurity, leading to a Cr 6+ -free Cr 3+ -activated ZnAl 2 O 4 :Cr 3+ ,Bi 3+ phosphor.