Trap and nonradiative centers in Ba₃Si₆O₁₂N₂:Eu²⁺ phosphors observed by thermoluminescence and two-wavelength excited photoluminescence methods.

Abstract

We have studied trap centers and nonradiative (NRR) recombination centers in a Ba3Si6O12N2:Eu2+ (BSON), one of promising materials for efficient and stable phosphors in white LED lamp applications. The energy distribution of four trap centers was obtained by thermo-luminescence (TL) with the excitation energy of 5.59eV. By superposing a below-gap excitation light of 1.77eV and observing the intensity change of the 5d-4f emission of Eu2+ centered at 2.36eV in our two-wavelength excited photoluminescence (TWEPL) measurement, both transient and steady state enhancement were observed. Such peculiar behavior of photo-stimulation is attributed to the coexistence of trap centers and NRR centers: the photoexcitation of electrons from trap centers generates the transient component, while that from NRR centers maintains the steady state component. An optical detection of relatively faint contribution of defects became possible in order to improve further the reliability and efficiency of phosphor materials.