Coexistence of the Eu2+ and Eu3+ Centers in the CaO : Eu Powder Phosphor

Abstract

Coexistence of the Eu2+ and Eu3+ centers is confirmed for two kinds of normalCaO:normalEu phosphors prepared in N2 and H2 by observing electron spin resonance (ESR) spectra, photoluminescence and optical excitation spectra and luminescence decay curves. The ESR signal intensity due to Eu2+ in normalCaO:normalEu prepared in H2 was about 7 times that in normalCaO:normalEu prepared in N2 . Details of the luminescence spectra of the Eu2+ centers in normalCaO are reported. The emission band of normalCaO:Eu2+ is located at 733 nm at 300 K, and the emission and excitation bands exhibit phonon structures at low temperatures. The luminescence lifetime of the Eu2+ center is about 1 μs at 300 K.

Valence States and Luminescence Properties of Ytterbium Ions in Strontium Haloborates

“…Therefore, the asymmetric shape of the 185 nm excitation band can be explained by the existence of several kinds of ytterbium centers in Sr B O X, namely the isolated Yb> center and the associated pair center of Yb> and strontium vacancy. Such a situation was reported for Eu> ions in CaO (20,21). The CT bands of CaO : Eu> have been observed at 235 nm for the Eu z !…”

Photoluminescence of Ba(SCN)2:Eu2+

“…In contrast, the position of the bands changes in many cases with the change of the cationic size. This is extreme for CaO:Eu 2+ [11] and SrO:Eu 2+ [12], where the emission maxima differ of more than 100 nm. On the other hand, the influence of the covalency of the host lattice seems to be large.…”

Tailoring of Deep‐Red Luminescence in Ca2SiO4:Eu2+

“…However, there have been a few reports of redemitting oxide phosphors excited by blue light in previous studies. [24,25] Therefore, we consider that the Ca 2 SiO 4 :Eu 2+ phosphors are interesting candidates as red-emitting oxide phosphors in white LEDs if its PL efficiency is further improved by the optimization of the preparation conditions such as use of flux reagent and heat-treatment. As mentioned above, the deep-red emission observed in Ca 2 SiO 4 :Eu 2+ in the present work should be associated with the occupancies of Eu 2+ ions in the Ca(2n) sites.…”