Excellent Upconversion Luminescence Obtained by Er³⁺ Self-Sensitization for Temperature Sensing in Deep Tissues and Anticounterfeiting Application

Abstract

The development of high-efficiency upconversion (UC) luminescent materials with multifunctional applications, particularly those excited by wavelengths within the second near-infrared (NIR) biological window, holds a paramount scientific significance. Herein, Er 3+ self-sensitization UC performance excited by 1532 nm wavelength is first studied in the CaSc 2 O 4 matrix. Strong green and red UC emission as well as 4 I 11/2 → 4 I 15/2 NIR transition are observed, though multipath optical thermometry with high sensitivity is realized. Moreover, the penetration depth of the 4 I 11/2 → 4 I 15/2 transition in the biological tissues can reach at least 6 mm, benefiting from its ideal excitation and emission wavelengths located in the biological window. Beyond that, CaSc 2 O 4: Er 3+ phosphor displays variable color luminescence under dual-wavelength excitation, including 980 and 1532 nm, which can be used for enhancing the security of anticounterfeiting materials. Our findings suggest that CaSc 2 O 4: Er 3+ phosphor with excellent UC properties is a promising candidate for the application in optical thermometry and anticounterfeiting field.