(Sr3Ca4)(Ca2Ga6)O18:Mn4+: crystallographic spatial isolation enables high doping levels, exceptional antithermal quenching, and promising temperature sensing applications

Abstract

Mn4+-activated oxide phosphors have been extensively studied as promising candidates for red phosphors. However, their practical applications are significantly hindered by severe thermal quenching and the inherently low absorption capability in blue light caused by low doping concentration. In this work, we report a novel Mn4+-activated phosphor series, (Sr3Ca4)(Ca2Ga6)O18:xMn4+ (SCCGO:xMn4+), where Mn4+ emitters are confined within well-separated perovskite-like structural units, spaced more than 10.9 Å apart. This special isolation effectively suppresses concentration quenching, thus enabling a high optimal doping level of x = 0.06, an order of magnitude higher than that in perovskites. The structural confinement effect also facilitates strong coupling between the Mn4+ red-emission and the local MnO6 octahedral vibrations, thereby resulting in tunable thermal quenching (TQ) behaviors. Impressively, Mg2+-modified phosphor SCCM0.25GO:0.045Mn4+ exhibits pronounced anti-TQ behavior, retaining 142% of its room temperature emission intensity at 423 K, outperforming hitherto reported Mn4+-activated phosphors. In contrast, SCCGO:0.03Mn4+ exhibits conventional TQ performance but demonstrates exceptional relative sensitivity (Sr = 4.70 % K-1 at 200 K) and outstanding temperature resolution (δT = 0.002 K), surpassing existing lifetime-based optical thermometers. The findings highlight the effectiveness of crystallographic confinement of Mn4+ emitters as a powerful strategy for designing multifunctional, high-performance Mn4+-activated oxide phosphors with superior luminescence thermal stability and advanced thermometric sensing capabilities.