Photon avalanche upconversion in TiO2∶Mo

Abstract

The Mo-doped titania exhibits a visible broadband emission under a 978 nm laser diode excitation. The luminescence has been assigned to the transitions from the excited states 3T1, 3T2 to the ground state 1A1 of the ［MoO4］2- radical. In TiO2∶Mo system, the p ower dependence of the upconversion-luminescence intensity exceeds a quadratic dependence, and the time evolution of the upconversion luminescence after the onset of continuous wave excitation is characterized by a rise time of 63 ms. These properties show the typical fingerprints of a photon avalanche. No luminescence was observed from the sample when excited with a pulsed laser (1064 nm) from a Nd∶YAG or a pulsed Raman-shift laser (953.6nm) pumped by a second harmonic of the Nd∶YAG. Regardless of the energy mismatch between the pulsed laser and the continuous wave diode laser, another reason may be that the duration time of a single laser pulse (10 ns) is much shorter than the rise time of the photon avalanche. The fluorescence “transfer function” theory is used to study the luminescence dynamics, which provides a good description of the experimental data.