Evidence of three different Eu2+ sites and their luminescence quenching processes in CaAl2O4:Eu2+

• CaAl2O4:Eu2+ shows 5d–4f and Eu trapped exciton (ETE) luminescence related to different Eu sites.
• The quenching temperature of 440, 540 and 650 nm PL are >300, 195 and 69 K.
• The photoconductivity related to Eu2+ in the two different sites was observed.
• Energy diagram of the 5d, ETE, 4f levels, VB and CB is determined in each Eu site.

We report the 5d–4f luminescence of Eu2+ and europium trapped exciton (ETE) luminescence in the different three crystallographic Ca sites in the Eu2+-doped CaAl2O4 and those quenching processes based on the results of the temperature dependence of photoluminescence and photoconductivity. The CaAl2O4:Eu2+ shows the 5d–4f luminescence peaked at 440 nm, 540 nm and the ETE luminescence peaked at 650 nm by UV and blue light excitation at low temperatures. The quenching temperature, at which the luminescence intensity is 50% of the intensity at low temperatures, of 440 nm, 540 nm and 650 nm bands are >300 K, 195 K and 69 K, respectively. The strong quenching for the 650 nm band is caused by the thermal ionization process, which was proved by the photoconductivity measurement. We also construct the vacuum referred binding energy diagram in each Ca site and discuss optical properties from the relative energy location between the 5d state, ETE state and conduction band.