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.

A reverse Monte Carlo (RMC) method is developed to obtain the energy loss function (ELF) and optical constants from a measured reflection electron energy-loss spectroscopy (REELS) spectrum by an iterative Monte Carlo (MC) simulation procedure. The method combines the simulated annealing method, i.e., a Markov chain Monte Carlo (MCMC) sampling of oscillator parameters, surface and bulk excitation weighting factors, and band gap energy, with a conventional MC simulation of electron interaction with solids, which acts as a single step of MCMC sampling in this RMC method. To examine the reliability of this method, we have verified that the output data of the dielectric function are essentially independent of the initial values of the trial parameters, which is a basic property of a MCMC method. The optical constants derived for SiO 2 in the energy loss range of 8-90 eV are in good agreement with other available data, and relevant bulk ELFs are checked by oscillator strength-sum and perfect-screening-sum rules. Our results show that the dielectric function can be obtained by the RMC method even with a wide range of initial trial parameters. The RMC method is thus a general and effective method for determining the optical properties of solids from REELS measurements. V C 2013 AIP Publishing LLC. [http://dx.

Eu(OH)3 rods, with diameters of 140 nm and lengths of 100−500 nm were prepared by a hydrothermal method. X-ray diffraction indicated a pure hexagonal phase (space group P63/m) of the rods. The relations between structural and optical properties of Eu(OH)3 rods under high pressures were obtained by photoluminescence (PL) and Raman spectra. Two structural phase-transition points at around 4 and 8 GPa were observed in this work. When a pressure of about 4 GPa was applied to the samples, one new emission peak at 593 nm was observed in the PL spectra, indicating the splitting of the 7F1 Stark level in Eu3+ ions. Such a splitting was attributed to the decrease of site symmetry of Eu3+ ions from C 3h to D 2 at high pressures. Two new Raman bands appeared under a pressure up to about 8 GPa due to the pressure-induced amorphization. After the pressure was released, the original PL and Raman spectra were recovered.

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