Photoluminescence and cathodoluminescence of BaAl₂O₄:Eu²⁺ and undoped BaAl₂O₄: evidence for F-centres

Abstract

In this article the photoluminescence (PL) and cathodoluminescence (CL) of undoped BaAl 2 O 4 and BaAl 2 O 4 doped with 500 ppm and 3 mol% Eu 2+ is described. The most important results from the CL measurements are: (1) Undoped BaAl 2 O 4 manifested intrinsic CL at 460 nm, which increased at low temperature and did not change significantly upon exposure to the e-beam; (2) Doping BaAl 2 O 4 with Eu 2+ changed the character of the intrinsic luminescence band: it became more sensitive to temperature variations and the band experienced a blue shift to ∼425 nm; (3) electron beam (e-beam) exposure of Ba 0.97 Eu 0.03 Al 2 O 4 at low temperature increased the 425 nm band strongly while the Eu 2+ emission at ∼500 nm decreased by about 70%. The Eu 2+ emission band was symmetric, indicating that BaAl 2 O 4 :Eu has changed to the P6 3 22 phase upon e-beam exposure at low temperature; (4) We have identified the 460 nm band in undoped BaAl 2 O 4 and the 425 nm band in BaAl 2 O 4 :Eu 2+ with F-centre luminescence, corresponding to the F-centre emission in α-Al 2 O 3. The evidence for the assignment of the 425 nm band in BaAl 2 O 4 :Eu 2+ is the spectacular increase of the spectral radiance at 425 nm by e-beam exposure at 200 keV and low temperature. A preliminary model is presented that explains the results. The PL from BaAl 2 O 4 :Eu 2+ quenched at the rather low temperature of 140°C; this observation is explained in terms of thermal ionization of the Eu 2+ ion.

Visualizing the valence states of europium ions in Eu-doped BaAl2O4 using X-ray nanoprobe mapping

“…The F-centre is a type of colour centre that is associated with an oxygen vacancy with two electrons (Wang et al, 2013;Ghamnia et al, 2003;Itou et al, 2009). den Engelsen, Fern, Ireland, Yang & Silver (2020) also observed an F-centre emission in the Eu-doped BaAl 2 O 4 phosphor via photoluminescence and cathodoluminescence.…”

Dy3+ Katkılı BaB4O7 Bileşiğinin Sentezlenmesi ve Optiksel Özelliklerinin Araştırılması

“…Literatürde bu durumlar ile ilgili çalışmalar vardır. Karbon katkılı Al2O3'te lüminesans emisyonun, oksijen anyon eksikliklerinden (F merkezlerinden) kaynaklandığı belirtilmektedir (Engelsen et al 2020, Zhou et al 2021, Akselrod et al 1998, Lee and Crawford, 1979. Baryum tetraborat bileşiği nominal olarak katkısız olduğundan, gözlemlenen parlak ışıma (emisyon merkezi) için olası aday olarak oksijen boşluğu kabul edilebilir.…”

Bluish-green afterglow and blue photoluminescence of undoped BaAl2O4

“…4 Irrespective of the difference in Re, the PL spectra of BaAl 2 O 4 :Eu 2+ ,Re 3+ are similar to that of Eu 2+ doped BaAl 2 O 4 (BaAl 2 O 4 :Eu 2+ ). 11–14 Consequently, Eu 2+ is generally assumed to be the luminescent center of afterglow and the luminescent center of PL for BaAl 2 O 4 :Eu 2+ and BaAl 2 O 4 :Eu 2+ ,Re 3+ . 1–18…”