Adamantane-Type Nitridophosphate Phosphors AE_xLi_10-2xP₄N₁₀ : Eu2⁺ via Medium-Pressure Ion-Exchange Reactions

Nitridophosphates have emerged as promising host compounds in the field of solid-state lighting. Their industrial relevance has increased significantly, mainly due to recent advances in synthetic approaches under medium-pressure (MP) conditions, including ammonothermal synthesis and hot isostatic pressing (HIP). In this study, we report on the synthesis and characterization of the quaternary representatives Ca_xLi_10-2xP₄N₁₀ (x=2, 2.7, 4) and Sr₃Li₄P₄N₁₀, prepared via a simplified ion exchange reaction under MP conditions, starting from the nitridophosphate-based lithium ion conductor Li₁₀P₄N₁₀. The synthesis route allowed for the preservation of the anionic [P₄N₁₀]^10- structural motif of the starting material, while simultaneously introducing potential doping sites for Eu²⁺ by incorporating divalent alkaline earth cations (Ca²⁺/Sr²⁺). Upon excitation of Eu²⁺ doped samples with blue light, strong luminescence due to parity-allowed 4f⁶(⁷F)5d¹→4f⁷(⁸S_7/2) transition can be observed in the red (Ca₂Li₆P₄N₁₀ : Eu²⁺: λ_max=626 nm), yellow/orange (Ca_2.7Li_4.6P₄N₁₀ : Eu²⁺: λ_max1=506 nm, λ_max2=592 nm and Sr₃Li₄P₄N₁₀ : Eu²⁺: λ_max=596 nm) and green (Ca₄Li₂P₄N₁₀ : Eu²⁺: λ_max=546 nm) spectral regions of the visible light. The compounds presented, together with the simplified synthetic approach, demonstrate the significant potential of ion exchange on Li ion conductors for the development of novel nitridophosphates in the future.