NaLaS₂:Yb/Tm蛍光体を介した電荷移動状態による赤色および近赤外線アップコンバージョン発光

The red and near-infrared (600-1100 nm) regions, known as biological "optical window" due to minimized tissue absorption and scattering, are vital for high-contrast deep-tissue imaging. Here, we report intense red (≈696 nm) and near-infrared (≈797 nm) emissions from NaLaS₂:Yb³⁺,Tm³⁺ under 980 nm excitation, both falling within this window. In addition to its enhanced chemical stability compared with conventional NaYF₄ host, the NaLaS₂ lattice effectively suppresses the typical blue emissions of Tm³⁺ (¹D₂ → ³F₄/¹G₄ → ³H₆, 450-500 nm) due to the overlap between the ¹D₂/¹G₄ states and the low-lying S^2- → Yb³⁺ charge transfer state (CTS) with an absorption edge extending to 560 nm. As a result, the red emission at 696 nm (³F_2,3 → ³H₆) and the near-infrared emission at 797 nm (³H₄ → ³H₆) dominate the spectrum. Furthermore, the thermal sensing performance of the NaLaS₂:Yb³⁺, Tm³⁺ sample was evaluated over a wide temperature (303-573 K) using fluorescence intensity ratio of the 696 nm and 797 nm emissions. It exhibits a maximum absolute sensitivity (S_A) of 0.122 K^-1 and a high relative sensitivity (S_R) of 0.896 % K^-1, which is significantly higher than that of other Yb³⁺, Ln³⁺ co-doped samples. These results highlight NaLaS₂:Yb³⁺, Tm³⁺ as a promising multifunctional luminescent material for deep-tissue bioimaging and high-performance optical thermometry.