The detection of foreign phases in Gd2O2S: Tb3+

Full text: The luminescence spectra at 20K of a series of 12 Tb3+doped Gd2O2S samples under several excitation conditions are investigated. The powder samples, from various origins, differ following the synthesis conditions, the grain dimensions, the Tb3+ content, the nature and concentration of added impurities. In non-selective experiments, the emission is excited at 355 nm by the third harmonic of a Q-switched neodymium YAG laser. Wavelength selectivity is ensured by the means of an optical parametric oscillator pumped by the neodymium laser. Simultaneous time-resolved measurements are obtained via a digital oscilloscope coupled with a microcomputer. In addition to the strong lines due to the dominating C3v site of Tb3+ in gadolinium oxysulfide, several sets of spurious lines are detected. They are enhanced by selecting the adequate 5D4 excitation wavelength. Nearly all the samples exhibit the same spurious lines, but the intensity of the various sets is different, depending on the samples. The origin of the additional lines is discussed and an assignment to possible and plausible impurity phases is attempted. The influence of the impurity phases on the intensity is discussed