Cathodoluminescence and Photoemission of Doped Lithium Tetraborate
Abstract
Lithium tetraborate (Li2B4O7) crystals are being developed for possible use in solid state neutron detectors. Already used in thermoluminescent dosimeters, enriched Li2B4O7 is of interest due to its large cross section for neutron capture by 6Li and 10B. The 6Li(n, alpha)3H and 10B(n, alpha)7Li reactions are the basis for neutron detection, and a Li2B4O7 crystal enriched with Mn should show improved efficiency for neutron detection. Li2B4O7 crystals doped with Mn significantly increases the light output in dosimeter applications. There is, however, a lack of fundamental characterization information regarding this useful material, particularly with regard to its electronic configuration. Photoemission spectroscopy was used to determine the energy level structure of the Mn doped Li2B4O7 crystals. Measurements were made using ultraviolet photoemission spectroscopy (UPS) at the Louisiana State University Center for Advanced Microstructures and Devices, using synchrotron radiation on two different beamlines. The first was the 3 m toroidal grating monochromator (TGM) beam line equipped with a 50 mm hemispherical electron energy analyzer providing a resolution of 70 mev and a photon energy range up to 95 eV. The TGM spectra confirmed the presence of Mn. The second was the normal incident monochromator (NIM) beamline equipped with a Scienta SES200 electron energy analyzer with a resolution of approximately 10 mev and a photon energy range from 24 to 32 eV to study the band gap states. Measurements were made at elevated sample temperatures to reduce charging effects. Photoemission studies provided evidence of Mn in the bulk crystal at 47.2 eV. Valence band analysis provided the presence of surface states but no acceptor sites. Cathodoluminescence studies were also made on undoped and Mn doped Li2B4O7 using excitation from a Kimball Physics EMG-12 electron gun and a Horiba half-meter Spectrometer. Measurements were made at various beam energies from 5-10 KeV and at room temp.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2011
- Accession Number
- ADA590997
Entities
People
- Christina Dugan
Organizations
- Air Force Institute of Technology