Powder Reflection Spectroscopy in the Vacuum uv range

• DOI: 10.1007/s10812-014-9934-5
• Publication Date: 2014-05-14T04:57:03Z
• Authors: D. Enseling; B. Herden; A. Katelnikovas; S. Möller; H. Winkler; R. Petry; H.-J. Meyer; T. Jüstela
• Keywords: Integrating sphere; Absorption edge

The measurement of diffuse refl ectance spectra below 230 nm for ceramic luminescent materials is usually not performed although it is of tremendous interest, e.g., to determine their quantum effi ciency upon VUV excitation. In contrast, the recording of VUV excitation spectra is well established, e.g., to evaluate VUV phosphors. The lack of access to diffuse powder refl ection spectra in this range is caused by the absorption edge (optical band gap) of the most common refl ectance standards; for instance, BaSO4 or CaCO3–VUV photons with energies higher than the absorption edge are not refl ected but absorbed and thus not amenable to detection in a synchronous scan. The measurement technique presented in this paper allows monitoring refl ection properties of powder samples in the range from 120 to 300 nm (10.3 to 4.1 eV). To this end, all VUV photons refl ected by the sample are converted into visible photons, which are collected in an Ulbricht sphere and fi nally counted by a photomultiplier tube (PMT). This requires a custom-built integrating sphere, viz. one that is coated with a (V)UV to Vis converter, e.g., a phosphor such as BaMgAl10O17:Eu2+ (BAM:Eu) showing a spectrally independent and high light output in the respective wavelength range. This paper sketches the technique and procedure for recording VUV refl ection spectra and shows the results for several standard phosphors. It also reveals the limits of this new technique.