First phosphite-bridging lanthanide–bismuth heterometallic selenotungstates and their ratio-metric-temperature luminescence sensing properties

Abstract

Designing luminescent materials with adjustable emission and high-temperature sensitivity in a rational manner remains a significant challenge in advanced temperature-sensing applications. Herein, we prepared two phosphite-bridging Ln^III–Bi^III heterometallic selenotungstates [H₂N(CH₃)₂]₈Na₂H₄[Ln₂W₃BiO₆(HPO₃)(H₂MA)(H₂O)₅]₂[B-α-SeW₉O₃₃]₄·52H₂O (Ln³⁺ = Eu³⁺, {Eu₄Bi₂P₂W₄₂}; Ln³⁺ = Tb³⁺, {Tb₄Bi₂P₂W₄₂}; H₆MA = mucic acid) by introducing [HPO₃]²⁻, Bi³⁺ and [SeO₃]²⁻ into the Ln³⁺/WO₄²⁻ system through a one-step self-assembly strategy. Their polyanions feature a mucic-acid-modified phosphite-bridging Ln^III–Bi^III heterometallic {[Ln₂W₃BiO₆(HPO₃)(H₂MA)(H₂O)₅]₂}¹⁸⁺ cluster connecting four [B-α-SeW₉O₃₃]⁸⁻ units. Luminescence measurements confirm the good luminescent properties of {Ln₄Bi₂P₂W₄₂}. Through the Eu³⁺/Tb³⁺ co-doping method, {Eu_4xTb_4−4xBi₂P₂W₄₂} doped-Ln–POMs were prepared, and energy transfer from Tb³⁺ to Eu³⁺ within the Eu_0.2Tb_3.8Bi₂P₂W₄₂ doped-material was observed, enabling tunable emission color from green to red under 365 nm UV irradiation. Furthermore, the ratio-metric-temperature luminescence sensing properties of the doped-Ln–POMs were systematically investigated. From 110 to 320 K, the luminescence intensities of Tb³⁺ and Eu³⁺ decrease due to the thermal activation of the non-radiative decay pathway. Notably, the Eu_0.2Tb_3.8Bi₂P₂W₄₂ doped material shows the highest relative sensitivity (S_r = 6.4% K⁻¹) and the lowest temperature uncertainty (δT = 0.36 K) at 320 K compared to other co-doping Ln–POM-based materials. This work not only offers a new approach for constructing innovative lanthanide–main-group heterometallic selenotungstates but also establishes a promising platform for the development of high-performance ratio-metric-temperature luminescence sensing.