On the Nature of the Luminescence of Sr[sub 2]CeO[sub 4]

Abstract

Recently efficient blue-white luminescence from Sr 2 CeO 4 was reported. 1 The emission was assigned to a ligand-to-metal chargetransfer transition of Ce 4ϩ . Charge transfer (CT) emission from Ce 4ϩ , or any other tetravalent lanthanide, had not been reported previously. Here, further research on the luminescence of Sr 2 CeO 4 is reported. Three topics are discussed. First the nature of the luminescence is investigated. The results provide evidence that the efficient blue-white emission is not related to a lattice defect and support the assignment of the emission to a Ce 4ϩ -O 2Ϫ CT transition. Second, lifetime measurements are discussed. The lifetime, 65 Ϯ 5 s at 6 K, is long for a parity allowed CT transition. The spin-forbidden nature of the emission can explain the observed lifetime. Finally, the temperature dependence of the emission intensity and luminescence lifetime is investigated. At 300 K both the emission intensity and the lifetime are reduced to about 50% of the values at 6 K. This shows that the quantum efficiency measured to be about 40% at room temperature is close to the maximum efficiency at room temperature. The low quenching temperature is a serious drawback for application of Sr 2 CeO 4 as a phosphor in lighting.

Optical and electrical characterization of samaria-doped ceria

“…All samples exhibit a high intensity and broad absorption band in the spectral range of 250-450 nm, assigned to the ligand-to-metal charge-transfer states O → Ce 4+ (LMCT) from O 2 2− ligand to Ce 4+ ion. The LMCT absorption bands are asymmetric and correlate with those of van Pieterson et al [22] who calculated the position of O → Ce 4+ LMCT absorption band of Sr 2 CeO 4 compound using an empirical formula of optical electronegativity data given by Jørgensen [23]. However, these two absorption bands observed for the Sr 2 CeO 4 system were related to different Ce 4+ -O 2 2− distances in the lattice.…”

“…Moreover, the tetravalent cerium ion (Ce 4+ , 4f 0 ) has an empty electronic configuration. The CeO 2 host exhibits a strong UV absorption arising from the ligand-to-metal charge-transfer states O → Ce 4+ (LMCT) from O 2 2− ligand to Ce 4+ ion that can act as a promising luminescent material [22]. Fig.…”

Hydrothermal synthesis and luminescent properties of LnPO4:Tb (Ln = La, Gd) phosphors under VUV excitation

“…Using (O) = 3.2 [15], (Tb) = 0.95 [16], the CTB of Tb 3+ in oxide can be calculated as 148 nm. So, the former is attributed to the CTB of Tb 3+ .…”

Inorganic Phosphor Materials for Lighting

“…In these materials the optical transitions are based on a ligand-to-metal charge transfer (CT) from O 2-to Ce 4? [122,123]. It was found that the addition of Sn 4?…”