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Title: Unusual Thermally Induced Blueshift and Emission Amplification of Mn²⁺ Ions Enable Filter-Free Luminescent Thermal Imaging

Authors: Y. Abe, M. Szymczak*, J. Zeler, L. Marciniak*

Journal: Advanced Science

DOI: 10.1002/advs.75943

The shift from point-based thermal sensing to filter-free thermal imaging requires luminescent thermometers that exhibit pronounced and thermally driven spectral changes within spectral regions matching the sensitivity profiles of the red, green and blue (RGB) channels of a digital camera. In this work, we introduce such a system, enabled by the synergistic interplay between (i) thermal redistribution among the vibronic components of the ⁴T₁ excited state of Mn²⁺ ions and (ii) thermally assisted population of this state via optical trap sites. These combined processes result in a simultaneous thermal enhancement and blueshift of the Mn²⁺ emission band associated with the ⁴T₁→⁶A₁ electronic transition. Consequently, the emission intensity recorded in the G channel increases with temperature, while the luminescence signals detected in the B channel exhibit a corresponding decrease. As demonstrated, Ca₁₉Zn₂(PO₄)₁₄:Mn²⁺, Ce³⁺ supports not only sensitive filter-free thermal imaging, but also two additional ratiometric readout schemes: one based on the intensity ratio of Ce³⁺ and Mn²⁺ emissions, and another based on two distinct spectral regions of the Mn²⁺ emission band, yielding maximum relative sensitivities of 0.42 and 2.7% K^-1, respectively. This approach introduces a unique thermometric strategy that enables simple, robust, and cost-effective two-dimensional thermal imaging without the need for optical filters or specialized instrumentation.

This work was supported by the Foundation for Polish Science under the First Team FENG.02.02-IP.05-0018/23 project with funds from the 2nd Priority of the Program European Funds for Modern Economy 20212027 (FENG).