Evaluation of Li2SnO3:Cr3+, Mn4+ as a dual-emitter luminescence sensor for cryogenic temperatures

Abstract

The sensitivity of luminescence properties in materials doped with transition metal (TM) ions to changes of temperature makes them particularly promising for thermometric applications. Designing and optimizing such materials requires a deep understanding of their structure, local environment of emission centres, and luminescence processes. In this work, we investigate the potential of Li₂SnO₃ doped with Cr³⁺ and Mn⁴⁺ as a dual-emitting luminescence temperature sensor. Li₂SnO₃ was chosen as the host material due to it being able to host both Cr³⁺ and Mn⁴⁺ at Sn octahedral positions. As a result, Mn⁴⁺ ions exhibit a distinctive ²E → ⁴A₂ line emission due to a strong crystal field, and Cr³⁺ ions experience an intermediate crystal field strength resulting in both, ²E → ⁴A₂ and ⁴T₂ → ⁴A₂ emissions. Through thorough examination, using powder X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and photoluminescence techniques we identified two distinct types of [SnO₆] octahedral centers that correspond to two types of slightly different Cr³⁺ and Mn⁴⁺ emission centers in the Li₂SnO₃ structure. The high sensitivity of the decay time constant for the ²E → ⁴A₂ emission of Li₂SnO₃–Cr³⁺, Mn⁴⁺ to temperature changes (2.0%/K at 190 K and 5.8%/K at 220 K for Cr³⁺ and Mn⁴⁺, respectively) positions the material as an attractive non-contact temperature sensor. Furthermore, application of such a dual-emitter luminescence material as a temperature sensor expands its sensitivity across a broader temperature range and offers the additional advantage of cross-checking measurements compared to materials solely doped with Cr³⁺ or Mn⁴⁺.