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

Abstract

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.