Tunable Upconversion Luminescence and Optical Thermometry in (Yb,Er) ₂ SiO ₅ /SiO ₂ Composite Phosphors

Upconversion luminescent materials have broad application prospects in lighting, display, and laser technology. However, single‐phase systems are constrained by performance bottlenecks, making it difficult to simultaneously achieve high temperature sensitivity and tunable luminescence. To address this challenge, (Yb x Er 1‐x ) 2 SiO 5 /SiO 2 multiphase composite phosphors are synthesized using a low‐temperature (300 °C) hydrothermal method. Under 976 nm excitation, the material exhibits concentration‐dependent luminescence: as the Yb fraction increases, the red emission at 660 nm continuously enhances, while the green emission shows initial enhancement followed by suppression. This behavior is attributed to an energy back‐transfer mechanism between Yb 3+ and Er 3+ ions. Regarding temperature sensing, a highly repeatable thermal response is observed through the fluorescence intensity ratio of Er 3+ levels. Specifically, the thermally coupled levels show a relative sensitivity of 1.91% K −1 , while the non‐thermally coupled levels exhibit an absolute sensitivity of 0.1063 K −1 . Furthermore, precise adjustment of Yb 3+ content, excitation power, or temperature enables continuous color tuning from green to red. This work simultaneously realizes high‐precision temperature sensing and dynamic luminescence color control in upconversion materials, providing novel design concepts and practical pathways for developing multifunctional optical materials.