The Raman and luminescence spectra of GdVO 4 :Eu 3+ microcrystals have been measured in the pressure range from ambient pressure to 16.4 GPa at room temperature by using a diamond anvil cell. The discontinuities on Raman mode and luminescence intensity and the appearance of new Raman bands and luminescence peaks have provided strong evidence for a phase transition at 7.4 GPa from zircon-type to scheelite-type structure, and the zircon-type and scheelite-type phases coexist over a pressure range of 7.4-16.4 GPa. The scheelite-type phase is retained after release of pressure.

The transition-metal oxide MoO 3 is an important semiconductor and has various technological applications in catalysts, electrochromic and photochromic devices, gas sensors, and battery electrodes. In this study, the hexagonal MoO 3 prepared by a hydrothermal method is in morphology of microrod with diameter of 0.8-1.2 mm and length of 2.0-4.3 mm. Its structural stability was investigated by an in situ Raman scattering method in a diamond anvil cell up to 28.7 GPa at room temperature. The new Raman peak around 1000 cm À1 implies that a phase transition from hexagonal to amorphous starts at 5.6 GPa, and the evolution of the Raman spectra indicates that the structural transition is completed at about 13.2 GPa. After releasing pressure to ambient condition, the Raman spectrum pattern of the high pressure phase was retained, revealing that the phase transition is irreversible.