Highly efficient latent fingerprint detection from NaYF4:Eu down-shifting microparticles

Each person's latent fingerprints (LFP) are unique and hardly change, so LFP detection provides essential clues in forensic science. Currently, the powder dusting method is being promoted for viewing LFP due to its environmental safety; however, its low efficiency, low sensitivity, and toxicity are drawbacks, restricting its applications. To overcome these points, we proposed a NaYF4:Eu3+ downshifting microparticle (DSMPs) phosphor synthesized by a hydrothermal method with intense emission of similar to 590-620 nm under excitation of 395 nm. We systematically studied the effect of synthesis conditions such as chelator, reaction time, temperatures, and doping concentrations on the structural, luminescent properties, and decay curves. The obtained results reveal that the crystal phase and particle morphology strongly depend on the reaction temperature. The emission properties of NaYF4:Eu3+ DSMPs can be significantly improved by changing the reaction temperatures and Eu doping contents. The optimized DSMPs with the most intense luminescent intensity were achieved when the phosphors were prepared at 180 C-degrees for 24 hours, the rare earth stearate/oleic acid ratio of 1:24, and Eu doping amount of 10 mol %. This finding contributes to the suppression of substrate interference in LFP detection. The prepared NaYF4:Eu3+ DSMPs address the earlier limitations and show good potential for LFP detection.