Unravelling the intrinsic luminescence in single-doped Yb3+ fiber microspheres for multi-mechanism optical thermometry

Trivalent ytterbium (Yb 3+ ) ions demonstrate a range of intrinsic luminescent properties, including cooperative luminescence, Stokes and anti-Stokes luminescence, and defect-related emissions, which extend significantly beyond their traditional role as sensitizers. However, the concurrent observation of such multi-mechanism luminescence within a single-doped material remains rare. Here, we unravel the intrinsic luminescence characteristics of Yb 3+ -doped fiber microspheres produced through CO 2 laser melting. Under 980 nm excitation, we identify four coexisting emission mechanisms: multi-ion cooperative luminescence, Stokes luminescence, phonon-assisted anti-Stokes luminescence, and defect-related luminescence from non-bridging oxygen hole centers (NBOHCs) in silica. The CO 2 laser reflow process is pivotal in activating this multi-mechanism behavior by promoting the formation of Yb 3+ dimers, enhancing phonon coupling, and introducing controlled defect states. Building on this intrinsic luminescence, we develop a multi-mechanism fluorescence intensity ratio (FIR) thermometer that combines thermally coupled Boltzmann-type transitions (Stark-splitting levels of Yb 3+ ) with non-Boltzmann strategies involving cooperative and defect-related emissions. The thermometer achieves high relative sensitivity and low temperature uncertainty over the range of 298–798 K, demonstrating rapid response and outstanding stability in real-time monitoring on ceramic heating plate. This work introduces a new approach for single-doped rare-earth optical thermometry by harnessing the luminescence capabilities of Yb 3+ , offering simplicity and reliable performance.