Vibrational properties of europium phosphate glasses

We have studied the vibrational properties of phosphate glasses containing Eu using optical and ultrasonic techniques. The fluorescence and absorption spectra show that the Eu is present only in the 3+ state. When compressed, these glasses show the remarkable property of becoming easier to squeeze. Measurements of the effect of uniaxial stress on ultrasonic wave velocities have been used to evaluate the temperature dependences of the third order elastic stiffness tensor component CIJK (TOEC) of 5 mol % Eu phosphate glasses between 77K and 400K. The acoustic mode Grueneisen 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