Blue light-induced rare-earth free phosphors for the highly sensitive and selective imaging of latent fingerprints based on enhanced hydrophobic interaction

The demand for in-situ detection of latent fingerprints (LFPs) in ways of high sensitivity, high selectivity, high contrast, low cost and user-friendly is still urgent. To overcome this challenge, a moisture-stable, red-emitting fluoride phosphor K₃AlF₆: Mn⁴⁺ (KAF: Mn⁴⁺) with an organic hydrophobic skin was prepared. The phosphor has a uniform and superfine morphology with excellent luminescence properties. More importantly, this non-ultraviolet (UV) or non-near infrared (NIR) induced phosphor was proved to be an ideal fluorescent label for LFP imaging, which is both friendly for touch DNA analysis and compatible to forensic light sources. The well-defined ridge details with little background interference on various surfaces were presented by the oleic acid (OA) modified KAF: Mn⁴⁺ (KAF: Mn⁴⁺-OA) phosphor in few seconds using the powder dusting method. To confirm the high selectivity of KAF: Mn⁴⁺-OA for LFP imaging, an efficient quantitative evaluation method is proposed with the aid of ImageJ & Origin software. Due to the superiority of the Mn⁴⁺-doped fluoride for the rapid imaging of LFPs in terms of low-cost, high compatibility and good availability, it is expected to be a promising candidate for forensic science as well as fluorescence imaging in other fields instead of rare earth luminescent materials.