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Title: Role of the Nephelauxetic Effect in Engineering Mn4+ Luminescence Kinetics for Lifetime-Based Thermometry

Authors: A. Basheer, M. Szymczak, M. Piasecki, A. M. Srivastava, M.G. Brik, L. Marciniak*

Journal:  Chemical Engineering Journal.

DOI: 10.1016/j.cej.2026.177734

Although the considerable potential of luminescence thermometry based on emission kinetics has been widely demonstrated, reliable tools for the intentional prediction of thermometric performance remain limited. To address this challenge, the present work introduces an approach that enables a theoretical description of the ²E-state lifetime of Mn⁴⁺ ions, as well as the absolute and relative sensitivities, in terms of the nephelauxetic effect within the group of double perovskites: Sr₂InNbO₆, Sr₂InTaO₆, Ba₂InTaO₆, and Ba₂InNbO₆. Our results clearly show that, contrary to common assumptions, for this particular group of phosphors the Dq/B ratio is not the primary factor governing either the spectroscopic behaviour of Mn⁴⁺ ions or the thermometric performance of Mn⁴⁺-doped phosphors. Instead, the nephelauxetic β₁ parameter plays the dominant role. The empirical analysis carried out in this study led to the development of a predictive model that enables estimation of S_AMAX and S_RMAX values based exclusively on β₁. This methodology represents a significant step toward the rational design of lifetime-based luminescence thermometers with predefined thermometric characteristics tailored to the requirements of specific applications.

This work was supported by the National Science Center (Poland) under 2023/49/B/ST5/03384 project.