Visible‐Light‐Excited Optical Thermometry in Ca ₃ Sc ₂ Si ₃ O ₁₂ : Er ³⁺ via an Efficient Eu ²⁺ Bridge

ABSTRACT Er 3+ ions are promising for optical thermometry due to their thermally coupled levels. However, their parity‐forbidden transitions result in weak and narrowband absorption, which restricts excitation to infrared lasers (e.g., 808, 980, or 1550 nm). Moreover, the single emission center inherently limits temperature sensitivity. In this work, we demonstrate that incorporating Eu 2+ ions into Ca 3 Sc 2 Si 3 O 12 : Er 3+ creates an efficient energy transfer bridge, enabling full‐visible‐spectrum excitation and a significant enhancement of Er 3+ ‐ion emission at 1540 nm. The Ca 3 Sc 2 Si 3 O 12 : Eu 2+ , Er 3+ phosphor achieves a high energy transfer efficiency of 66.56% and excellent temperature‐sensing performance, with a maximum absolute sensitivity ( S a ) of 5.05% K −1 at 473 K and a relative sensitivity ( S r ) of 2.34% K −1 at 293 K. A portable optical thermometry system excitable by visible light and featuring dual‐band near‐infrared (NIR) emission was developed. Moreover, a NIR phosphor‐converted light‐emitting diode (pc‐LED) was fabricated based on the optimized Ca 3 Sc 2 Si 3 O 12 : Eu 2+ , Er 3+ phosphor, demonstrating its potential for applications in night‐vision imaging and nondestructive testing.