Sustainable fabrication of ZnGa2O4:Eu3+ phosphors via Aloe Vera for optical thermometers, dermal ridge detection and counterfeit deterrence

Abstract

This study introduces an eco-friendly synthesis method using Aloe Vera (A.V.) as a biosurfactant for hydrothermal synthesis of (0.5–9 mol %) Eu³⁺ doped ZnGa₂O₄ (ZGO:Eu³⁺) self-assembled superstructures. Metal oxide phosphors like ZGO have garnered interest for their versatile applications in catalysis, gas sensing, and biomedical engineering. Key synthesis parameters, A.V concentration, pH, sonication time, mechanical stirring, and sonication power are optimized to control the morphology, size, and shape of the resulting superstructures. Photoluminescence (PL) studies demonstrated effective energy transfer from the ZGO host to Eu³⁺ ions under 393 nm excitation, predominantly via dipole-dipole interactions. The ZGO:5Eu³⁺ phosphor exhibits a high internal quantum efficiency (I_QE) of 83.49 % and excellent thermal stability, retaining 88.93 % of its luminescence intensity at 420 K. Furthermore, it demonstrates high absolute (3.92 % K⁻¹) and relative (0.010 K⁻¹) thermal sensitivities, highlighting its potential for temperature sensing and white light emitting diode (w-LED) applications. A w-LED is successfully fabricated, achieving a correlated color temperature (CCT) of 5335 K, a high color rendering index (R_a = 92), and CIE coordinates of (0.336, 0.335). Additionally, the phosphor showed outstanding performance in detecting latent fingerprints (LFPs), poroscopy, anti-counterfeiting (AC) labels, and luminescent hydrogel applications, demonstrating its versatility across diverse surfaces. This adaptability enhances its utility in forensic investigations and biometric security, enabling accurate FP visualization in diverse scenarios. These findings demonstrate that ZGO:Eu³⁺ phosphors hold great potential for applications in LFP detection, security inks, and w-LEDs.