The search for defects in undoped SrAl2O4 material

Abstract

SrAl2O4:Eu,Dy is a very efficient long afterglow phosphor with wide range of possible applications. The lumi-nescence properties and the possible luminescence mechanism of this material have been studied extensively, but there is almost no information available about the undoped material. Therefore, this article deals with the luminescence and thermally stimulate d luminescence of an undoped SrAl2O4, revealing the possible defects that might be involved in the creation of the long afterglow in doped material. We conclude that undoped material exhibits some luminescence under X-ray irradiation in low temperature; close to room temperatures lumines-cence is almost fully thermally quenched in comparison to low temperatures. We can observe F and F2 center luminescence as well as trace metal luminescence in the emission spectrum. TSL glow curve yields the peaks that are close to those observed in material with Eu and Dy doping; therefore these peaks are clearly related to intrinsic defects. The peak at around 400 K, that is shifting with rare earth doping, might be due to dopant interaction with intrinsic defects.

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

“…The agreement between Fig. 3, which refers to undoped BaAl 2 O 4 , and the spectrum of undoped SrAl 2 O 4 at low temperature [32] is surprisingly good, taking into account the preliminary character of the deconvolution presented in Fig. 3.…”

“…In the introduction we have mentioned some recent studies on the intrinsic luminescence of undoped BaAl 2 O 4 [33][34][35][36][37] and undoped SrAl 2 O 4 [32]. Since the published spectra of undoped BaAl 2 O 4 show substantial differences, there is no obvious way to select an appropriate spectrum for comparison.…”

“…Vitola et al [32] assigned the 435 nm band in undoped SrAl 2 O 4 to an F-centre and the 510 nm band to an F 2 -centre. The luminescence of these defects in α-Al 2 O 3 and γ-Al 2 O 3 has been well described in the literature [39][40][41][42][43][44][45][46] and as mentioned by Vitola et al [32], the wavelength of the luminescence peaks does not depend strongly on the crystal structure, α-or γ-Al 2 O 3 . This was confirmed by Zorenko et al [44], who determined λ 0 of the F-centre luminescence in YAG at 464 nm and in YAP at 423 nm.…”

“…In our work on Sr 1−x Ca x Al 2 O 4 :Eu 2+ [4] we have elaborated on this alternative hypothesis and proposed that the origin of the 440 nm band in SrAl 2 O 4 is due the luminescence of an F-centre. This proposal has been based on the work of Vitola et al [32].…”

“…In addition to the second point in the summary of the most important results presented above, it is worthwhile to mention that the F-centre luminescence in BaAl 2 O 4 and SrAl 2 O 4 behave differently. The undoped BaAl 2 O 4 manifests clearly F-centre luminescence at room temperature, whereas in undoped SrAl 2 O 4 the F-centre luminescence (excited by X-rays [32]) is quenched at room temperature. In the doped materials the behaviour is not so different: in both BaAl 2 O 4 :Eu 2+ and SrAl 2 O 4 :Eu 2+ the F-centre luminescence is quenched at room temperature.…”