Thermal history forensics using the emission intensity ratio of YVO4:Eu3+ phosphor

We demonstrate the thermal history forensic measurements founded on the emission intensity ratio of Eu3+-doped yttrium vanadate. An increase in phosphor’s crystallite size with annealing temperature is observed, causing a significant and permanent increase in the emission intensity and symmetry ratio (ratio of Eu3+ 5D0 → 7F1 and 5D0 → 7F2 emissions). This ratio is used as a forensic indicator of the maximal temperature to which phosphor was exposed. Additionally, we demonstrated that irreversible change in the symmetry ratio after exposure to high temperatures is insensitive to the exposure time. Finally, it is shown that thermal history readings can be performed at any temperature. The applicative potential of the proposed approach was confirmed in the proof-of-concept experiment on a steel plate covered with phosphor and exposed to high temperatures.