High resolution spectroscopy to investigate impurity traces in YAB single crystals

The work explores the feasibility of high resolution (as fine as 0.02 cm-1) Fourier transform spectroscopy applied at 9 K in the 500-25000 cm-1 range to detect traces of unwanted impurities, mainly rare earths (RE3+)in crystals: the system chosen is YAl3(BO3)4 (YAB). Weak traces of RE3+ (Nd, Dy, Er, Tm, Yb), but also of Cr3+ and OH-, were successfully monitored by comparing the spectra of YAB samples under examination with those intentionally doped with a given ion. The analysis performed on a variety of samples shows how Cr3+, Nd3+, and Yb3+ are the most frequent unwanted dopants and can provide suggestions to the crystal growers about the performances of different crystal growth lines. According to a preliminary evaluation, the Er3+ traces detection limit is as low as 1-2×10-4 mol% in 1 cm thick samples. The advantages of the method, which is sample non-destructive, are discussed in comparison with those currently applied.