A detailed aging analysis of MPO4:X (M = Y3+, La3+, Lu3+; X = Bi3+, Pr3+, Gd3+) due to the Xe excimer discharge

Mike Broxtermann*, Lena Marie Funke, Jan Niklas Keil, Hellmut Eckert, Michael Ryan Hansen, Andries Meijerink, Ting Yu, Norbert Braun, Thomas Jüstel

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

Phosphate hosts doped with luminescent ions are widely applied for efficient spectral conversion in light emitting devices. However, in Xe discharge lamps a rapid degradation of light output is observed indicating a decrease in the efficiency of conversion of the VUV output of the Xe discharge. This work aims at providing a better understanding of the degradation mechanism. We summarize peculiar findings made within a survey of different inorganic UV emitting phosphors of the MPO4:X (M = Y, La, Lu; X = Bi, Pr, Gd) type regarding their stability under operation in a dielectric barrier Xe excimer discharge lamp. Test lamps containing these phosphors as a particle layer coating onto the inner wall of the lamp vessel suffer from a rapid degradation which was monitored by the loss of UV radiation output during lamp operation. The thus aged materials were recovered and further analysed by optical spectroscopy. It turned out that the aged materials do not only exhibit a new broad absorption in the UV/visible range, which explains the rapid decline of radiation output during lamp operation, but also that all aged materials show photoluminescence in the red upon exposure to UV radiation. It is argued that this luminescence originates from phosphorus in the oxidation state +III (configuration: [Ne]3 s2) which is present as a point defect. These defects are formed when the respective materials are aged in direct contact with the Xe excimer discharge within the lamp discharge vessel. This detailed study of phosphor aging by means of VUV luminescence spectroscopy as well as temperature and time dependent luminescence spectroscopy and solid state EPR spectroscopy points to the existence of phosphorus +III ([Ne]3 s2) which shows characteristic ns2 luminescence which has not been reported before.

Original languageEnglish
Pages (from-to)450-460
Number of pages11
JournalJournal of Luminescence
Volume202
DOIs
Publication statusPublished - 1 Oct 2018

Funding

The authors are grateful to the German Federal Ministry of Education and Research (BMBF) and MB and LF further acknowledge the Foundation of German Economy for generous financial support. Support by FAPESP (CePID project 2013–07793-6 ) to HE is also acknowledged. Special thanks are due to Prof. Dr. Rainer Pöttgen, WWU Münster for taking some XRD measurements and to the whole Fluoro UV BMBF project team for the fruitful cooperation. Appendix A

Keywords

  • Decay constants
  • EPR Spectroscopy
  • Lamp aging
  • Ns luminescence
  • Phosphorus
  • Solid state NMR
  • Temperature and time dependent spectroscopy
  • UV phosphors
  • VUV spectroscopy
  • Xe excimer discharge

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