Fundamental Loading‐Curve Characteristics of the Persistent Phosphor SrAl₂O₄:Eu²⁺,Dy³⁺,B³⁺: The Effect of Temperature and Excitation Density

Abstract

The compound SrAl2O4:Eu2+,Dy3+ is currently one of the best‐performing persistent phosphors and numerous studies have been performed to understand the mechanisms involved in its afterglow process. One aspect which so far has received only limited attention is the dependence of loading curve characteristics on dopant concentrations. Herein, a detailed study of the loading curves of SrAl2O4:Eu2+,Dy3+ as a function of composition, sample temperature, and pump intensity is presented, completed by emission decay and quantum yield measurements. The observed emission decays can be described using the Inokuti−Hirayama equation for a Dexter energy transfer (ET) process. As the Dexter ET rate and the electron transfer rate have a similar radial dependence, the Inokuti−Hirayama equation can also describe the electron transfer process involved for the trapping process. These observations indicate that in this persistent phosphor, the trapping process is a local process; however, different types of traps appear to present different “Dexter” critical radii R0. This electron transfer is also temperature dependent, which requires further investigations.

Recent Progress in Inorganic Afterglow Materials: Mechanisms, Persistent Luminescent Properties, Modulating Methods, and Bioimaging Applications

“…Diaz-Torres and co-workers reported that Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ ,Bi 3+ phosphors with different bismuth concentrations always decrease the emission spectra and afterglow time, [204] which can be attributed to the formed quenching centers. In other systems, like ZnGa 2 O 4 :Cr 3+ ,Bi 3+ , [90a] Ca 3 Ga 2 Ge 3 O 12 :Cr 3+ ,Bi 3+ , [172b] Zn(Ga 1-x Al x ) 2 O 4 :Cr 3+ ,Bi 3+ , [181a] ZnGa 2 O 4 :Cr 3+ ,B 3+ , [205] SrAl 2 O 4 : Eu 2+ ,Dy 3+ ,B 3+ , [35,206] Ca 0.85 Zn 0.15 TiO 3 :Pr 3+ ,B 3+ , [152] Ca 2 Zn 4 Ti 16 O 38 : Pr 3+ ,B 3+ , [79] and Sr 4 Al 14 O 25 :Eu 2+ ,Dy 3+ ,B 3+ , [207] a certain extent of PL improvements were present, while the mechanisms are divergent, such as the suppression of the self-reduction effect of Cr 3+ , [90a] formation of the electron traps as the Cr 3+ -Bi 3+ couple, [172b] and probably increased depth or concentration of the traps. [35,205] Obviously, further and deep studies are in urgent need.…”

Exploring the luminescence of tin‐incorporated nickel‐sensitized lithium gallate short‐wave‐infrared phosphors

“…It is evident that the incorporation of Sn 4+ into the phosphor lattice significantly lowers the QY. The results of the quantum efficiency test demonstrate that the rate of trapping in Sn‐doped phosphors is significantly higher than the rate of radiative emission 29 . The process of determining the QY, using an integrated sphere, is illustrated in Figure S7a–e.…”

“…This can also explain why we observe a significant reduction in QY of emission, decreasing from around 21% to 5% because of the presence of Sn 4+ . 29…”

Control of stoichiometry in garnet crystals presenting persistent luminescence

“…Thicker transparent crystals (1.5 mm thickness) exhibit more intense afterglow than thinner transparent crystals (0.6 mm thickness) as a larger volume of the sample could be excited in the inner part of the material (see data in Figure 2). This can be expressed as a volume effect [28,29] . Indeed, the initial intensity is about 1.7 times higher for the 1.5 mm crystals in regards to the 0.6 mm crystal.…”