Red emitting CaTiO₃: Pr³⁺ nanophosphors for rapid identification of high contrast latent fingerprints

Red emitting (~612 nm) CaTiO₃:Pr³⁺ long afterglow nanocrystals with a persistence time ~20 min (dark adapted human eyes) have been synthesised for developing high contrast latent fingerprints using the sol-gel process. Due to the persistent emission, CaTiO₃:Pr³⁺ nanophosphor does not require a continuous source for excitation, thereby eliminating the background information even from multi-colour substrates, resulting in a high signal to noise ratio. As a consequence of which, minute features of level- I, II and III can be clearly studied in high contrast fingerprints. Considerable blue shift (~20 nm) was recorded in photoluminescence excitation due to the quantum confinement properties of CaTiO₃:Pr³⁺ nanocrystals. Powder x-ray diffraction confirms the formation of a single phase orthorhombic structure of CaTiO₃:Pr³⁺ with average crystallite size ~40 nm. Spectral parameters indicate a very high color purity of 99% with CIE coordinates (0.62, 0.37) which are very close to NTSC standards for an ideal red-emission. Transmission electron microscopy studies confirm the formation of spherical particles with narrow size distribution which makes them suitable to combine with fingerprint development methods such as powder dusting and cyanoacrylate fuming methods.