2004/04/29 by A E R Malins, A.E.R. Malins, N R J Poolton +7 · 2 citations
Materials Science · #Glass properties and applications #Luminescence Properties of Advanced Materials #Nuclear materials and radiation effects
paper · doi:10.1088/0022-3727/37/10/005
The first comprehensive survey of band-edge features in the ternary group of naturally occurring aluminosilicates (the feldspars) is presented. Synchrotron-based luminescence excitation of KAlSi3O8, NaAlSi3O8 and CaAl2Si2O8 allows the measurement of the evolution of the band-gap across the system, which, at 8 K, is found to vary from 7.86 eV in NaAlSi3O8 to 7.7 eV and 7.62 eV in KAlSi3O8 and CaAl2Si2O8, respectively: the band-gap energies are typically 0.1 eV smaller at 300 K. In comparison with measurements made on natural and synthetic hydrothermal α-quartz, where both the direct and indirect band-gap structures are distinctly observable, no significant post-edge band structure is discernable in the feldspars. In Ca-rich material, the luminescence is attenuated by more than two orders of magnitude for excitation energies up to 3 eV above the band-gap, partly supporting the proposition (derived from previous cyclotron resonance experiments) that the bands are simply parabolic and that the materials may be direct band-gap insulators. The luminescence excitation experiments also allow an initial survey to be made of sub-band-gap features in the materials, including low mobility, temperature sensitive band-tail states and mid-gap defects.