Stable narrowband red emission in fluorotellurate KTeF5:Mn4+ via Mn4+ noncentral-site occupation

Unlike conventional central-site doping, herein, abnormally equivalent Mn4+ accommodation in a five-fold coordinated distorted octahedron in the vertical occupation site is reported in fluorotellurate KTeF5:Mn4+. This very unique substitution results in thermally stable (remaining emission of 86.7% at 423 K) and highly purified red emission in KTeF5:Mn4+. Refined contrasts of the coordination environment, crystal field, nephelauxetic effect, temperature-dependent static and dynamic luminescence behavior, and defect mechanism between fluorides with different Mn4+ accommodation models (K2SiF6:Mn4+, K2NaAlF6:Mn4+, KTeF5:Mn4+, K3ZrF7:Mn4+, K2TaF7:Mn4+ and Na3TaF8:Mn4+) are conducted to investigate the local environment dependence of the Mn4+ emission properties. It is found that the emission of KTeF5:Mn4+ might be stabilized by equivalent octahedral Mn4+ accommodation with interstitial defects. These findings reveal the possible effects of special accommodation models on the Mn4+ emission properties, which further enlighten us to explore stable fluoride red phosphors with suitable Mn4+ accommodation for white light-emitting diode applications.