A photoluminescence study of REE3+ emissions in radiation-damaged zircon

A series of natural zircon samples (with U concentrations of 140-2600 ppm and ranging from well crystalline to severely radiation damaged) were investigated by means of REE3+ photoluminescence spectroscopy. We found systematic changes in REE3+ emissions depending on the accumulated radiation damage expressed by the effective time-integrated alpha dose of zircon samples. Structural reconstitution as caused by dry annealing resulted in intensity gains and decreases of half-widths of REE3+ emissions. The band half-widths of distinct luminescence Stark's levels of the F-4(9/2) -> 6H(13/2) transition of Dy3+ (similar to 17250 cm(-1); 580 nm wavelength) and the F-4(3/2) -> I-4(9/2) transition of Nd3+ (similar to 11 300 cm(-1); similar to 885 nm wavelength) were found to correlate sensitively with the degree of radiation damage accumulated. These REE3+ emissions are proposed as potential measure of the irradiation-induced structural disorder of zircon. The two emissions are considered particularly suitable because (1) they are commonly detected in PL spectra of natural zircon, and (2) they are hardly biased by other emissions or Stark's levels. Preliminary calibration curves that relate band-width increases to the a dose were established using a suite of well-characterized Sri Lankan zircon. Band broadening upon increasing corpuscular self-irradiation is assigned to increasing structural destruction, i.e., the increasing perturbation of REE3+ cationic lattice sites. Possible advantages of REE3+ luminescence spectroscopy, complementary to Raman spectroscopy, as method to quantify structural radiation damage are discussed.