Laser-induced time-resolved spectroscopy of visible broad luminescence bands in zircon

This work examines the luminescence of zircon studied by laser-induced time-resolved methods. This method allows the differentiation between luminescence centers of similar emission wavelengths, but different decay times. Samples include a suite of natural zircons, nominally pure synthetic ZrSiO₄, and ZrSiO₄ artificially doped by Mn, Fe, Cr, Ni, Co, Pb, Sb, Ti, Ta, V, Sc, U, U-P, and Th-P. In addition, pure ZrSiO₄ samples irradiated by thermal neutrons have been studied. We have clarified the nature of several luminescence bands reported previously from time independent studies, and suggest the following as the causes of luminescence in zircon systems: 1) the yellow band with peak wavelength (λ_max) = 575nm, peak half-width (Δ) = 120-130nm, and decay time (τ) = 30-35μs is connected with neutron and alpha irradiation, 2) the green band with λ_max = 505nm and vibrational structure is linked to the presence of the uranyl ion, but it is only observed in artificial samples with codoping by U and P, 3) the red band with λ_max = 750nm, Δ = 110-120nm and τ = 3-5ms is connected with Fe³⁺. We have also identified new luminescence bands, obscured by stronger emissions. These are: emission a) with λ_max = 480nm, Δ = 70-80nm and τ = 300-325μs, emission b) with λ_max = 515nm, Δ = 90-100nm and τ = 500-520μs, emission c) with λ_max = 605nm, Δ = 110-125nm and τ = 8-10μs. These emissions have not been detected in synthetic doped zircons and their interpretation remains the subject of further investigation.