Optical thermometry, latent fingerprint detection and anti-counterfeiting based on upconversion emission in Ho3+/Yb3+ doped KYF4 nanoparticles

Abstract

The structural, morphological, and optical properties of the KYF4:Ho3+/Yb3+ upconversion nanoparticles were investigated in this work. In the upconversion emission studies, emissions at 544 nm, 657 nm, and 740 nm resulting from the transitions 5F4 (5S2) → 5I8, 5F5 → 5I8 and 5F4(5S2) → 5I7, respectively, of the Ho3+ ion were observed. Temperature sensitivity was determined from temperature-dependent upconversion spectra, and it was found to be 1.32% K−1 for the synthesized upconversion nanoparticles. Additionally, the nanoparticles were utilized to detect latent fingerprints on the glass, and the recorded images show good contrast. Upconversion nanoparticles were also used to create the invisible ink, and the written words were subsequently recorded using upconversion emission mode.