Structural Confinement Induced Near‐Unity Quantum Yield for Single‐Band Ratiometric Thermometry

Abstract Luminescence quenching at high dopant concentration and temperature typically limits the brightness of luminescence materials, which remains a major obstacle in diverse technological applications, especially in the field of luminescence thermometry. In this work, a unique class of non‐concentration quenching double‐tungstate phosphors is reported that feature the near‐unity quantum yield of Tb 3+ and Eu 3+ emissions induced by the structural confinement effect. Mechanistic studies affirm that the activator ions can be isolated in NaYW 2 O 8 crystal to confine the absorbed photon energy, leading to a relatively high quenching concentration of various lanthanide activators. By facilitating interionic cross‐relaxation at heavy dopant concentration, a remarkable thermal enhancement of Tb 3+ emissions over 20‐fold upon the excitation of excited‐state absorption is recorded. In contrast, thermally quenched emissions are detected under the excitation of ground‐state absorption. This excitation wavelength‐dependent thermal behavior of Tb 3+ emissions is harnessed for single‐band ratiometric thermometry, registering superior thermal sensitivity and resolution ( S r = 4.01% K −1 , δT = 0.1 K). The advances in combating concentration and thermal quenching of luminescence materials provide exciting opportunities for flexible thermometry in real‐world sensing scenarios.