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 K 5 La(MoO 4 ) 4 : x Eu 3+ (KLMO: x Eu 3+ ) 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 5 D 0 - 7 F 2 transition of Eu 3+ . The optimal doping concentration of phosphors is 0.8 mol. The quenching temperature of the KLMO:0.80Eu 3+ phosphor was found to exceed 480 K, with high activation energy ( E a ) of 0.43 eV, showing good thermal stability. Impressively, the KLMO:0.80Eu 3+ phosphor with a 0.8 mol concentration of Eu 3+ 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:0.80Eu 3+ phosphor was surface-functionalized with oleic acid (OA) (KLMO:0.80Eu 3+ @OA) to help better identify Level I-III fingerprint details with high resolution and contrast. The results show that the KLMO:Eu 3+ and KLMO:Eu 3+ @OA phosphors have very promising applications in the w-LEDs and latent fingerprints (LFPs).