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

Abstract

In the past few decades, efficient photon upconversion (anti-Stokes) luminescence has been extensively studied and is almost exclusively restricted to lanthanide (Ln³⁺) 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⁺ → Ln³⁺ → Mn⁴⁺ in specially prepared Yb³⁺/Ln³⁺/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 Ln³⁺ as well as the intermediate crystal field environment of Mn⁴⁺ in the YAlO₃ host, the possibility of using a Mn⁴⁺/Ln³⁺-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.