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Photoluminescence and cathodoluminescence of BaAl 2 O 4 :Eu 2+ and undoped BaAl 2 O 4 : evidence for F-centres

2020; Optica Publishing Group; Volume: 10; Issue: 8 Linguagem: Inglês

10.1364/ome.10.001962

2159-3930

Daniel den Engelsen, George R. Fern, Terry G. Ireland, Fengli Yang, Jack Silver,

Glass properties and applications

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.