Time-resolved and temperature-dependent spectroscopy for blue luminescence of monoclinic YSiO2N:Ce3+ phosphor

Abstract

The monoclinic YSiO2N activated with Ce3+ ions was synthesized, and its luminescence spectra were investigated to reveal the energy level structure of the Ce3+: 5d excited states. Depending on excitation wavelengths, two types of photoluminescence bands in violet and blue regions are observed, which differ in spectral shapes and thermal quenching behaviors. While one of them can easily be assigned to the Ce3+: 5d1 → 2F5/2, 2F7/2 transitions from the major sites, the other shows an anomalously broad weak luminescence band for the latter band. The time-resolved spectroscopy shows a luminescence lifetime distribution of 33–58 ns in the range of 440–540 nm that is also typical for the Ce3+: 5d1 levels. It is suggested that the broad luminescence bands and the distribution of Ce3+ luminescence lifetimes are due to various minor Ce3+ centers with slightly different coordination environments probably caused by intrinsic or anti-site anion defects. By analyzing the temperature dependence of decay curves for Ce3+: 5d luminescence, the activation energy for thermal quenching and the quenching temperature are estimated to be 0.272 eV and 422 K, respectively. The vacuum-UV spectroscopy found out the five separated 5d excitation levels, leading to the estimated centroid energy of 5d levels, 33112 cm−1.