Unveiling the subtle emission transition of dysprosium in CaWO4 crystals for ultra-sensitive ratiometric thermometry and anti-counterfeiting applications

Dy 3+ -doped luminescent materials have a promising application in various optical and optoelectronic fields. The unveiling of detailed energy level distribution and subtle emission transition of Dy 3+ in oxide matrices is vital for developing new optical sensors . In this study, the crystallographic site symmetry of Dy 3+ in CaWO 4 :Dy 3+ phosphors prepared via the co-precipitation method was identified by the XRD , FT-IR, and Raman spectroscopy . The spectroscopic site of the S 4 symmetry of Dy 3+ in CaWO 4 crystals was confirmed using Eu 3+ as the structural probe through high-resolution, low-temperature photoluminescence spectroscopy. The detailed crystal-filed (CF) energy level arrangement and corresponding emission transition lines of Dy 3+ were revealed through the spectral well-resolving and temperature-dependent PL spectra . Furthermore, a new ratiometric thermometric strategy based on the two opposite thermal-dependent CF transitions exhibited excellent sensitivity to a wide temperature range from 80 to 700 K. In addition, a novel barcode anti-counterfeiting applicability has been certified to realize dynamic information encryption . This study provides insight into the development of new Dy 3+ -based phosphors and the exploration of CaWO 4 :Dy 3+ phosphors in advanced luminescent thermometers and anti-counterfeiting under extreme temperature conditions.