Ln3+-Sensitized Mn4+ near-infrared upconverting luminescence and dual-modal temperature sensing

In the past few decades, efficient photon upconversion (anti-Stokes) luminescence has been extensively studied and is almost exclusively restricted to lanthanide (Ln(3+)) doped fluorophores. However, investigations on upconversion emissions of transition metal activators, whose (Stokes) luminescence is known to be tunable via modifying the crystal-field of the hosts, are extremely scarce. In the present work, a strategy to achieve Mn4+-based room-temperature near-infrared upconversion luminescence with the aid of efficient energy transfer of Yb3+ -> Ln(3+) -> Mn4+ in specially prepared Yb3+/Ln(3+)/Mn4+ (Ln = Er, Ho, Tm): YAlO3 products is reported for the first time. Steady-state and time-resolved upconversion emission spectra are adopted to systematically clarify the related energy transfer mechanisms and determine energy transfer efficiencies. Benefitting from the completely different thermal-quenching mechanisms of Mn4+ and Ln(3+) as well as the intermediate crystal field environment of Mn4+ in the YAlO3 host, the possibility of using a Mn4+/Ln(3+)-based dual-emitting upconversion fluorescence intensity ratio and Mn4+ upconversion lifetime as dual-modal temperature signals for accurate temperature sensing is demonstrated. It is believed that this preliminary study will offer a significant advance in exploring novel transition metal-based upconversion materials as well as self-calibrated optical thermometric media.