Thermal and concentration dependent energy transfer of Eu^2+ in SrAl_2O_4

Abstract

SrAl 2 O 4 doped with europium and dysprosium is a powerful and widely used afterglow material. Within this material strontium is found in two crystallographic different sites. Due to the similar ion radii and same charge, Eu 2+ -ions can occupy both sites, resulting in two different Eu 2+ -ions, one emitting in the blue and one in the green spectral range. The blue emission is thermally quenched at room temperature. In this paper we investigate the energy transfer between different Eu ions depending on the concentration and temperature using two different approaches: lifetime measurements and integrated intensity. We find an activation energy for the thermal quenching of the blue emission of 0.195 ± 0.023 eV and a critical radius for the energy transfer of 3.0 ± 0.5 nm. These results can help in designing better afterglow materials due to the fact that with energy transfer parts of the lost emission in the blue region at room temperature can be converted to the green site.

Two-color thermosensors based on [Y $$_{1-x}$$ 1 - x Dy $$_x$$ x (acetylacetonate) $$_3$$ 3 (1,10-phenanthroline)] molecular crystals

“…In addition to the thermal quenching affecting the emission intensity we also find that it affects emission lifetime, which is consistent with previous measurements of other lanthanide-doped complexes [77,[81][82][83]. We characterize the influence of thermal quenching on the lifetime of [Y 1−x Dy x (acac) 3 (phen)] by measuring the lifetime of the emission at 482 nm and 575 nm for the 10 mol% sample, as shown in Figure 12.…”

“…where c 0 is the critical concentration [81] and k D is a material dependent constant. From the functional forms of Equations 3 and 4 we note that LRET results in the lifetime asymptotically approaching zero, while the Dexter mechanism has the lifetime asymptotically approaching a nonzero value.…”

Counting the Photons: Determining the Absolute Storage Capacity of Persistent Phosphors

“…The field of persistent luminescent materials gained importance with the discovery of SrAl${}_2$O${}_4$:Eu,Dy by Matsuzawa et al [1], replacing ZnS:Cu,Co [2] as the benchmark afterglow phosphor. This green emitting phosphor shows afterglow for several hours after the excitation has stopped, and has been extensively investigated [3,4,5]. Two decades after the discovery by Matsuzawa et al, the list of afterglow phosphors has grown, and in addition to the alkaline earth aluminates it now also includes, among others, silicates and sulfides doped with a wide variety of activators, such as Eu${}^{2+}$ [6], Ce${}^{3+}$ [7,8] or transition metal ions [9].…”

Feature issue introduction: persistent and photostimulable phosphors – an established research field with clear challenges ahead

“…In a systematic study, Bierwagen et al focussed on the luminescence intensity and lifetime of both emission bands as a function of temperature and of europium concentration in SrAl 2 O 4 :Eu [18]. Although the blue emission band quenches around room temperature, energy transfer to the green emission center rescues the overall efficiency of the phosphor.…”