Structural changes of europium stannate pyrochlore, Eu 2 Sn 2 O 7 , have been investigated at high pressures with in situ Raman spectroscopy, photoluminescence (PL), and synchrotron x-ray diffraction (XRD) techniques. The XRD measurements suggest that a pressure-induced phase transition starts at 34.4 GPa. The PL spectrum from Eu 3+ cations also suggests a phase transition above 36 GPa. XRD analysis shows that the unit cell of the cubic phase deviates from the equation of state at pressures above 23.8 GPa. This is due to the incorporation of water from the pressure medium in the structure at high pressures, which is confirmed by optical spectroscopy measurements.

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The crystal structure and light emission property of Yb/Tm doped gadolinium titanate and gadolinium zirconate with chemical composition of A 2 B 2 O 7 were studied by x-ray diffraction (XRD) and optical spectroscopy measurements, respectively. XRD results suggest that the rare earth titanates have an ordered pyrochlore structure and a defect-fluorite structure for the zirconates. Photoluminescence activated with 1064 nm infrared laser light shows different light emission behaviors for the titanate and zirconate samples, which is related to the different site occupancy of Tm 3+ in the lattice of the samples. Only a weak near-infrared (NIR) (~800 nm) light emission was observed in the titanate samples while a strong blue and red up-conversion emission was detected in the Tm 3+-doped zirconate samples. The strong blue and red emission is due to the 7-fold coordinated Tm 3+ in the structure.

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