Coupling of carbon dots in Eu3+ doped dicalcium silicate, derived from marine and agro-waste, offers a luminescent armor for counterfeiting, improving thermal sensing and advancing forensic explorations

Abstract

A series of red-emitting composite based on carbon dots in β-Ca₂SiO₄:Eu³⁺ (CDs@CSO:Eu³⁺) nanocomposites (NCs) were synthesized through a solid state (SS) method, aiming to enhance applications in latent fingerprints (LFPs), lip prints (LPs) detection, anti-counterfeiting (AC) techniques and optical thermometry. The powdered X-ray diffraction (PXRD) analysis confirmed the monoclinic crystal structure of the phosphor. Under 394 nm excitation, the Eu³⁺ doped β-CSO:Eu³⁺ display a broad red emission peak at 615 nm, attributed to the ⁵D₀→⁷F₂ transition of Eu³⁺ ions. The optimal concentration of Eu³⁺ ions is determined to be 3 mol %, as higher concentrations led to a decrease in photoluminescence (PL) emission intensity due to concentration quenching (CQ). Additionally, a fabricated white light emitting diode (w-LED) using these phosphors achieved chromaticity coordinates of (0.355, 0.352) according to the Commission International de L'Eclairage (CIE), with the CIE, correlated colour temperature (CCT), and colour purity (CP) metrics indicating a bright green output with values of (0.6122, 0.3499), 1177 K, and 88.7%, respectively. The optimized 3wt % CDs@β-CSO:3Eu³⁺ composite demonstrated a remarkable CP of 97.7 %. Notably, the composite maintained 92.6 % of their emission intensity at 420 K, showcasing exceptional thermal stability. The internal quantum efficiency (I_QE) is an impressive 85.8%, demonstrating the effectiveness of the process. This study explores the application of composite materials for LFPs detection and cheiloscopy. Utilizing advanced phosphor composites, we achieved enhanced visualization of fingerprints (FPs) features, including level I (ridge patterns), level II (minutiae points), and level III (ridge details such as pores and scars). Additionally, the composite's efficacy is demonstrated in cheiloscopy, capturing detailed LPs across type I to VI categories. The results highlight the composite's superior performance in both fingerprint and LP analysis, offering improved resolution and reliability for forensic applications. In addition, a novel approach is employed via brush mode to create AC patterns using optimized security ink. The resulting AC tags featured high resolution and durability. These findings underscore the 3wt%CDs@β-CSO:3Eu³⁺ composite as superior luminescent materials for use in fields requiring LFP, AC strategies, and optical thermometry.