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Notes: Abstract To investigate how the local symmetry of the Sm3+ ion affects the fluorescence of a samarium metaphosphate glass of composition (Sm2O3)0.248(P2O5)0.752, the temperature and pressure dependences of its laser induced fluorescence spectrum are compared with those of a samarium pentaphosphate crystal (SmP5O14). Findings include: (i) The crystal field splitting of the energy levels responsible for fluorescence in SmP5O14 at room temperature is consistent with the local symmetry of oxygen atoms of the phosphate cage around the Sm3+ ions being quite close to cubic – in accord with crystal structure. At 12 K there is a systematic disappearance of the shortest wavelength lines of each fluorescence band attributable to a decreasing population of higher crystal field levels, which are occupied at ambient temperature. (ii) The (Sm2O3)0.248(P2O5)0.7520.248 glass fluorescence spectrum forms five bands, which can be related to that of the crystal but with inhomogeneous line broadening; the short wavelength edges sharpen at low temperatures, also attributable to a decreasing population of higher crystal field levels at lower temperatures. (iii) The shifts (dλ/dp) in the wavelengths of the fluorescence peaks of the SmP5O14 crystal induced by pressure up to 50 kbar in a diamond anvil cell are small but measurable at room temperature, being about +0.03 nm kbar−1 (+0.3 Å kbar−1). Application of pressures up to 50 kbar to the (Sm2O3)0.248(P2O5)0.752 glass did not alter the positions of the bands within the error in the fluorescence wavelength measurements. Neither the SmP5O14 crystal nor the metaphosphate glass showed any indication of undergoing a phase transition up to the highest pressure reached. A low frequency Raman mode has been observed, which softens with reducing temperature, indicating softening of the associated optical mode and suggesting that, like other RP5O14 crystals, SmP5O14 undergoes a ferroelastic phase transition.

Notes: Abstract To provide an overall picture of the vibrational properties of phosphate glasses containing high concentrations of europium, measurements have been made of their ultrasonic wave velocities and attenuation, optical absorption spectra and laser-induced fluorescence. To examine their valence state, the fluorescence of the glasses has been examined. The spectra do not show any obvious sign of divalent europium ions, only trivalent europium ion fluorescence being observed. Room-temperature absorption spectra of these glasses also provide evidence of only the absorption bands of trivalent europium. The elastic stiffnessesC 11 andC 44 continue to increase down to low temperatures and the ultrasonic attenuation is characterized by a broad peak, properties which are consistent with thermally activated relaxations of two-level systems. The longitudinal and shear ultrasonic wave velocities decrease under pressure; the hydrostatic pressure derivatives (∂C 11/∂P) T, P=0 and (∂C 44/∂P) T, P=0 of the elastic stiffness tensor componentsC IJ and (∂B/∂P) T, P=0 of the bulk modulus,B 0, are negative. When compressed, the europium phosphate glasses, like their samarium analogues, show the interesting property of becoming easier to squeeze. Measurements, using a pulse superposition technique, of the effect of uniaxial stress on ultrasonic wave velocities have been used to determine the temperature dependences of the third-order elastic stiffness tensor components of (Eu2O3)0.186(P2O5)0.814 and (Eu2O3)0.20(P2O5)0.80 glasses between 77 and 400 K. The uniaxial and hydrostatic pressure dependences of the elastic constants quantify the cubic term in the strain Hamiltonian and the vibrational anharmonicity of the long-wavelength phonons of these glasses. The acoustic mode Grüneisen parameters are negative: application of pressure induces a decrease in the long-wavelength acoustic phonon mode frequencies. As the temperature is reduced the pressure-induced mode softening becomes enhanced. The hydrostatic pressure derivative (∂C 11/∂P) T, P=0 is larger than (∂C 44/∂P) T, P=0 over the whole temperature range, and the longitudinal acoustic mode Grüneisen parameter ∥γL∥ is larger than that ∥γS∥ of the shear wave: the longitudinal mode softens more with pressure than the shear mode. Murnaghan's equation-of-state is used to determine the compressionV(P)/V 0.