Latent fingermarks light up: facile development of latent fingermarks using NIR-responsive upconversion fluorescent nanocrystals

NaYF4:Yb,Er and NaYbF4:Er/Tm/Ho NIR-responsive upconversion fluorescent nanocrystals were used to develop latent fingermarks on the surfaces of various substrates. Development exhibited high developing contrast, high developing sensitivity, and high developing selectivity. In particular, one-year-old fingermarks, fingermarks on wet substrates, and fingermarks on surfaces with multicolored background and strong fluorescent properties could be clearly observed through our method.