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Open AccessArticle

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

1
Lumilab, Department of Solid State Sciences, Ghent University, Krijgslaan 281 S1, 9000 Gent, Belgium
2
Department of Chemistry and Biochemistry and Center for Nanoscience Research, Concordia University, Montreal, QC H4B 1R6, Canada
*
Author to whom correspondence should be addressed.
Materials 2017, 10(8), 867; https://doi.org/10.3390/ma10080867
Received: 29 June 2017 / Revised: 16 July 2017 / Accepted: 24 July 2017 / Published: 28 July 2017
The performance of a persistent phosphor is often determined by comparing luminance decay curves, expressed in cd/m 2 . However, these photometric units do not enable a straightforward, objective comparison between different phosphors in terms of the total number of emitted photons, as these units are dependent on the emission spectrum of the phosphor. This may lead to incorrect conclusions regarding the storage capacity of the phosphor. An alternative and convenient technique of characterizing the performance of a phosphor was developed on the basis of the absolute storage capacity of phosphors. In this technique, the phosphor is incorporated in a transparent polymer and the measured afterglow is converted into an absolute number of emitted photons, effectively quantifying the amount of energy that can be stored in the material. This method was applied to the benchmark phosphor SrAl 2 O 4 :Eu,Dy and to the nano-sized phosphor CaS:Eu. The results indicated that only a fraction of the Eu ions (around 1.6% in the case of SrAl 2 O 4 :Eu,Dy) participated in the energy storage process, which is in line with earlier reports based on X-ray absorption spectroscopy. These findings imply that there is still a significant margin for improving the storage capacity of persistent phosphors. View Full-Text
Keywords: persistent luminescence; storage capacity; strontium aluminate; calcium sulfide; rare earths persistent luminescence; storage capacity; strontium aluminate; calcium sulfide; rare earths
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MDPI and ACS Style

Van der Heggen, D.; Joos, J.J.; Rodríguez Burbano, D.C.; Capobianco, J.A.; Smet, P.F. Counting the Photons: Determining the Absolute Storage Capacity of Persistent Phosphors. Materials 2017, 10, 867.

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