Distinctive Ce3+ luminescence from single-crystalline and glassy Ce:LaB3O6

Abstract

Ce³⁺ luminescence depends on both the composition and the structure of host materials, whereas the role of the structure is still not well understood. In this work, Ce:LaB₃O₆ (LBO) in both single crystalline and glassy forms are synthesized, and their distinctive photoluminescence (PL) and X-ray radioluminescence (XRL) are compared and discussed for the first time from the points of view of structure and defects. Crystalline Ce:LBO exhibits a very narrow PL band centered at 303 nm and a small Stokes shift of 3098 cm⁻¹, while the glassy Ce:LBO emission is broad and bluish, peaking at 396 nm, with a larger Stokes shift of 4778 cm⁻¹. The PL of crystalline Ce:LBO is constant over the whole cryogenic temperature range until the steep Mott–Seitz quenching mechanism starts even below RT. Its PL decay is characterized by a short and single-exponential lifetime of about 15 ns, corresponding to a quantum efficiency (QE) of ∼50%. In contrast, glassy Ce:LBO shows an even higher QE but its PL decreases gradually from the He temperature up until 400 °C with a bi-exponential decay characteristic. Moreover, radio- and thermo-luminescence measurements indicate the presence of a much larger population of defects in glassy than in crystalline Ce:LBO. All the observed luminescence differences mainly stem from the distinct local structures of Ce³⁺, being a unique single-site in a regular periodic lattice in the case of crystalline Ce:LBO and non-equivalent sites in amorphous glassy Ce:LBO, as found by means of X-ray atomic pair-distribution function analysis and high-resolution transmission electron microscopy. These results provide new insights into the host structure's contribution to the dopant's luminescence properties.