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

Unlike conventional central-site doping, herein, abnormally equivalent Mn 4+ accommodation in a five-fold coordinated distorted octahedron in the vertical occupation site is reported in fluorotellurate KTeF 5 :Mn 4+ . This very unique substitution results in thermally stable (remaining emission of 86.7% at 423 K) and highly purified red emission in KTeF 5 :Mn 4+ . Refined contrasts of the coordination environment, crystal field, nephelauxetic effect, temperature-dependent static and dynamic luminescence behavior, and defect mechanism between fluorides with different Mn 4+ accommodation models (K 2 SiF 6 :Mn 4+ , K 2 NaAlF 6 :Mn 4+ , KTeF 5 :Mn 4+ , K 3 ZrF 7 :Mn 4+ , K 2 TaF 7 :Mn 4+ and Na 3 TaF 8 :Mn 4+ ) are conducted to investigate the local environment dependence of the Mn 4+ emission properties. It is found that the emission of KTeF 5 :Mn 4+ might be stabilized by equivalent octahedral Mn 4+ accommodation with interstitial defects. These findings reveal the possible effects of special accommodation models on the Mn 4+ emission properties, which further enlighten us to explore stable fluoride red phosphors with suitable Mn 4+ accommodation for white light-emitting diode applications. Unlike conventional central-site doping, here, we firstly report a stable Mn 4+ emission in novel fluorotellurate KTeF 5 via Mn 4+ abnormally equivalent and penta-coordinated octahedral vertical-site occupation.