Spectroscopy of gadolinium gallium garnet crystals doped with Y b3 + revisited
The optical spectroscopy measurements of gadolinium gallium garnet (GGG) crystals doped with Yb show evidence of the presence of non-equivalent optical centers with very similar radiative decay rates. The energy level schemes of those centers have been determined on the basis of optical absorption, luminescence and Raman experiments. Crystal field fitting resulted in two sets of slightly different crystal field parameters for two non-equivalent Yb centers. Both sets of parameters describe perfectly the experimentally detected Y b3 + energy levels. Correlation between systematic trends in the experimental energy level schemes and crystal field parameters is discussed.
Optical spectroscopy of Yb3+-doped Ca3Sc2Ge3O12 garnet crystal
Good quality Ca3Sc2Ge3O12 garnet crystals activated with Yb3+ have been grown by means of the flux growth method and characterized using optical spectroscopy techniques. The low-temperature absorption and emission spectra give evidence of the presence of nonequivalent optical centers, as a consequence of the distribution of the Yb3+ ions in different lattice sites. The effect of codoping with Na+ or Mg2+ on the Yb3+ site distribution has been investigated. The energy-level schemes of the most important centers have been determined on the basis of site-selective spectroscopy experiments. Cooperative luminescence has also been observed and reliably compared with the self-convolution of the NIR luminescence.
Site selection and up-conversion studies in erbium and ytterbium doped CsCdBr3
A detailed study of absorption and fluorescence lines of transitions between excited state 4S32 and ground state 4I152 has been carried out in several doped and codoped samples. Polarized absorption confirmed the C3v site symmetry of Er3+. Using laser excitation in the 4F72 level, three kinds of Er3+ sites have been observed and attributed to Er3+ -vacancy-Er3+, Er3+-Er3+-vacancy dimers and isolated ions in single doped compounds. In codoped samples the same experiments showed that Er3+, Yb3+ pairs are formed. Up-conversion under infrared and red excitation results in emissions between 380 and 670 nm and confirms the results obtained under direct excitation. Finally, other parameters for anti-Stokes emissions have been measured under low power infrared excitation, including the dependence of fluorescence intensity with incident power and temperature.