(Sr ₃ Ca ₄ )(Ca ₂ Ga ₆ )O ₁₈ :Mn ⁴⁺ : crystallographic spatial isolation enables high doping levels, exceptional anti-thermal quenching, and promising temperature sensing applications

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:<i>x</i>Mn⁴⁺ (SCCGO:<i>x</i>Mn⁴⁺), 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 <i>x</i> = 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, the Mg²⁺-modified phosphor SCCM_0.25GO: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 (<i>S</i>_r = 4.70% K^-1 at 200 K) and outstanding temperature resolution (δ<i>T</i> = 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.