A novel red-emitting K5La(MoO4)4:Eu3+ phosphor with a high quantum efficiency for w-LEDs and visualization of latent fingerprints

A new series of red luminescent K5La(MoO4)4:xEu3+ (KLMO:xEu3+) phosphors (x = 0.05–1.00 mol) was successfully synthesized by a high-temperature solid phase reaction at a low reaction temperature (600 ℃). The X-ray diffraction (XRD) pattern, photoluminescence properties, thermal quenching mechanism, quantum efficiency, and lifetime decay curves of the phosphors were measured and discussed in detail. The prepared phosphors exhibited strong red-light emission (at 615 nm) upon excitation at 394 nm, attributed to the electric dipole 5D0-7F2 transition of Eu3+. The optimal doping concentration of phosphors is 0.8 mol. The quenching temperature of the KLMO:0.80Eu3+ phosphor was found to exceed 480 K, with high activation energy (Ea) of 0.43 eV, showing good thermal stability. Impressively, the KLMO:0.80Eu3+ phosphor with a 0.8 mol concentration of Eu3+ doping also has an internal quantum efficiency (IQE) of up to 84.5%. The packaged white light emitting diode (w-LED) showed a good color rendering index (CRI) (89), correlated color temperature (CCT) (5117 K), and the Commission International de L′Eclairage (CIE) chromaticity coordinates (0.342, 0.345). Furthermore, the KLMO:0.80Eu3+ phosphor was surface-functionalized with oleic acid (OA) (KLMO:0.80Eu3+@OA) to help better identify Level I-III fingerprint details with high resolution and contrast. The results show that the KLMO:Eu3+ and KLMO:Eu3+@OA phosphors have very promising applications in the w-LEDs and latent fingerprints (LFPs).