Investigating the influence of carbon dots on β-Ca2SiO4:Ce3+ phosphors derived from agro-waste for diverse applications

A series of blue-emitting composite based on 3 wt% carbon dots in β-Ca2SiO4:Ce3+ (3 wt% CDs@β-CSO:Ce3+) was synthesized through a hydrothermal method, aiming to enhance applications in latent fingerprint (LFP) detection, anti-counterfeiting (AC) measures, and optical thermometry. The X-ray diffraction (XRD) analysis confirmed that these phosphors possess a monoclinic crystal structure. Under 356 nm excitation, the Ce3+ doped β-Ca 2SiO4 phosphors (β-CSO:Ce3+) display a broad blue emission peak at 431 nm, attributed to the 5d → 4f electric dipole transition of Ce3+, while the inclusion of Carbon dots (CDs) shifts this emission to 442 nm. This shift and the improved photoluminescence (PL) intensity are thought to result from the Fӧrster Resonance Energy Transfer (FRET) mechanism. The optimal concentration of Ce3+ ions was determined to be 5 mol%, as higher concentrations led to a decrease in emission intensity due to concentration quenching (CQ). Additionally, a fabricated white light diode using these phosphors achieved chromaticity coordinates of (0.344, 0.330) 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 (0.1486, 0.0433), 1759 K, and 96.4%, respectively. The optimized 3 wt% CDs@β-CSO:5Ce3+ composite demonstrated a remarkable CP of 99.9%. Notably, the phosphors maintained 85.77% of their emission intensity at 423 K, showcasing exceptional thermal stability. A novel approach utilizing sketch pen and brush mode was developed to apply the optimized AC security ink, allowing for the creation of various intricate patterns. The resulting AC tags featured high resolution and durability. These findings underscore the 3wt%CDs@β-CSO:5Ce3+ composite as superior luminescent materials for use in fields requiring LFP, AC strategies, and optical thermometry.