Exploring calibration-free luminescence thermometry with Mn 4+ anti-Stokes/Stokes emission

Abstract

Mn 4+ -activated phosphors offer a unique possibility of calibration-free primary luminescence thermometry using the ratio of anti-Stokes to Stokes (AS/S) vibronic emission lines of the 2 E → 4 A 2 transition. Previous work used the AS/S emission of Mn 4+ for thermometry but always relying on fitting procedures with effective vibrational energies that deviate from actual energies. Here, we explore a strategy without prior temperature calibration using two well-known Mn 4+ -doped hosts, Mg 14 Ge 5 O 24 (MGO) and K 2 SiF 6 (KSF). In both Mn 4+ occupies octahedral sites, replacing Ge 4+ or Si 4+ , resulting in a weak zero-phonon line (ZPL) and strong vibronic Stokes and anti-Stokes lines. From the temperature-dependent emission spectra the AS/S ratios ν 6 ′/ν 6 , ν 4 ′/ν 4 , ν 3 ′/ν 3 were determined to serve as input for luminescence intensity ratio (LIR) analysis. For the well-resolved vibronic lines of Mn 4+ in KSF it is feasible to realize temperature readout without temperature calibration – a capability rarely achieved in luminescence thermometry. In contrast, for Mn 4+ in MGO vibronic lines exhibit significant overlap, complicating single-phonon-mode modeling. Even spectral deconvolution methods do not allow for reliable calibration-free temperature sensing. This work establishes a generalizable approach to optical thermometry relying on anti-Stokes/Stokes vibronic lines, offering a path towards calibration-free temperature sensing.