Blue long lasting phosphorescence of Tm3+ in zinc pyrophosphate phosphor

Phosphate long lasting phosphorescence (LLP) phosphors with composition of (Zn1−xTmx)2P2O7 were prepared by the high-temperature solid-state method. Their properties were systematically investigated utilizing XRD, photoluminescence, phosphorescence and thermoluminescence (TL) spectra. These phosphors emit blue light that is related to the characteristic emission due to the 1D2–3H6, 1D2–3H4 and 1G4–3H6 transitions of Tm3+. After the UV light excitation source was switched off, the bright blue long lasting phosphorescence can be observed which could last for more than 1 h in the limit of light perception of dark-adapted human eyes (0.32 mcd/m2). Two TL peaks at 336 K and 415 K appeared in the TL spectrum. By analyzing the TL curve the depths of traps were calculated to be 0.67 eV and 0.97 eV, respectively. Also, the mechanism was discussed in this report.