On the “Bi3+–Ti4+” charge transfer transition in the pyrochlore Y2Ti2O7:Bi3+

• Spectroscopic properties of Bi3+ in Y2Ti2O7 is examined.
• The host crystallizes in the pyrochlore structure.
• The luminescence is attributed to Bi3+–Ti4+ charge transfer transition.
• The Bi3+ ground state is located 0.40 eV from top of valence band.

We have studied the low temperature (15–300 K) spectroscopic properties of Bi3+ impurities in the pyrochlore Y2Ti2O7. The spectroscopic properties of Y2Ti2O7:Bi3+ are interpreted on the basis of the Bi3+(6s2)–Ti4+(4d0) metal-to-metal charge transfer transition that is caused because the Bi3+1S0 ground state (6s2) energy occurs at about 0.40 eV from the top of the O2− 2p band (valence band). The reason for the low quenching temperature of the charge transfer luminescence is established. A comparative study of the Bi3+ luminescence in the pyrochlores Y2Ti2O7, Y2Sn2O7 and La2Zr2O7 is presented. The Bi3+1S0 ground state (6s2) energy is located about 0.46 eV from the top of the O2− 2p band in La2Zr2O7.