Phonon-assisted Cross-relaxation Research Articles

Optical study of CaNdAlO 4

Crystal structure and optical properties of single crystals of CaNdAlO 4 were studied. The results of X-ray measurements on single crystal samples were used to perform the vibrational analysis and to discuss the luminescence properties of the crystal. It was concluded that the occurrence of luminescence in this compound, in spite of the high neodymium concentration, is due to the limited efficiency of phonon-assisted cross relaxation.

Relaxation of the [formula omitted] level of Nd 3+ IN BaLa 1−xNd xGa 3O 7

Single crystals of BaLa 1− x Nd x Ga 3O 7, where 0 ⩽ x ⩽ 0.2, were investigated experimentally using the methods of conventional spectroscopy and crystallography. Structural data and the results of vibrational analysis were employed to interpret the temperature and concentration dependence of excitation decay in the crystals. It has been found that in diluted samples the relaxation process is consistent with multiphonon emission involving high energy Ga-O vibrations. In concentrated samples the excitation decay is governed by phonon-assisted cross relaxation via the 4I 15 2 intermediate level and by a thermally-triggered quenching process, which is supposed to be the energy transfer to structural defects, acting as energy sinks, accelerated by excitation energy migration on Nd 3+ ions.

Fluorescence Studies of Energy Transfer between Single and PairCr3+Systems inAl2O3

The fluorescence intensities and lifetimes of various no-phonon lines in ruby samples with 2.1 and 0.94% ${\mathrm{Cr}}^{3+}$ were studied from 13 to 700\ifmmode^\circ\else\textdegree\fi{}K. The temperature dependences of the intensities of numerous lines were used to determine the energy levels of two pair systems. The relative intensities of the single-ion ($R$) lines and the pair ($N$) lines are proportional to Boltzmann factors ${e}^{\frac{\ensuremath{-}\ensuremath{\Delta}E}{\mathrm{kT}}}$, where $\ensuremath{\Delta}E$ is the difference in energy of the metastable states, at high temperatures but not at low temperatures. The deviation from this law is greater and occurs at higher temperatures in the less concentrated sample. The fluorescence decays of the $R$ and $N$ lines are pure exponentials in the temperature region where the $N$ lines follow a Boltzmann law; at low temperatures the $N$ lines have an initial rise in fluorescence and then a decay. These results are interpreted in terms of coupled fluorescence systems consisting of single ions and pairs. A phonon-assisted cross-relaxation coupling process is suggested which allows for thermalization of the systems at high temperatures and direct pumping of the pair systems by the single-ion system at low temperatures. Energy transfer from single-ion to multi-ion systems was also observed.