Achieving a Eu2+-doped NIR phosphor via ionic modulation and its multifunctional applications

Abstract

Latent fingerprint (LFP) detection is an important tool in criminal offense detection. Nowadays, ultraviolet (UV) excited visible emission phosphors are widely used in LFP detection; however, due to the shortcomings of UV excitation (λ_ex < 270 nm) such as low power, high price, and susceptibility of visible light to the influence of natural light, their application in LFP detection is restrained. Here, a new idea is proposed: the use of blue light-excited near-infrared (NIR) emitting phosphors as a tool for fingerprint detection visualization. To this end, in this work, a series of blue-excited (λ_ex = 467 nm) NIR phosphors Ca_(1−x)Sr_xO:Eu²⁺ (x = 0–0.2) were designed based on CaO:Eu²⁺ by using the crystal field engineering strategy. When x = 0.2, the luminescence center is red-shifted from 733 nm to 783 nm, and the full width at half maximum (FWHM) is broadened from 100 nm to 156 nm, and the red-shift and broadening of the spectrum greatly improve the accuracy of fingerprint detection. Finally, Ca_0.8Sr_0.2O:0.1%Eu²⁺ gives high-quality visualized fingerprints in LFP detection, which is a good solution to the problems faced by UV-excited visible-emitting phosphors in LFP detection. Not only that, a NIR phosphor-converted light-emitting diode (NIR pc-LED) was prepared by combining Ca_0.8Sr_0.2O:0.1%Eu²⁺ with a blue LED chip, which was verified to have the potential for applications in biological tissue penetration and night vision illumination. This work introduces a new idea for the detection of a LFP and demonstrates that rationalizing the local structure around Eu²⁺ is an effective strategy for exploring Eu²⁺-doped NIR luminescent phosphors.