The role of the Eu3+ concentration on the SrMoO4:Eu phosphor properties: synthesis, characterization and photophysical studies.

SrMoO(4) doped with rare earth are still scarce nowadays and have attracted great attention due to their applications as scintillating materials in electro-optical like solid-state lasers and optical fibers, for instance. In this work Sr(1-x)Eu(x)MoO(4) powders, where x=0.01; 0.03 and 0.05, were synthesized by Complex Polymerization (CP) Method. The structural and optical properties of the SrMoO(4):Eu(3+) were analyzed by powder X-ray diffraction patterns, Fourier Transform Infra-Red (FTIR), Raman Spectroscopy, and through Photoluminescent Measurements (PL). Only a crystalline scheelite-type phase was obtained when the powders were heat-treated at 800 °C for 2 h, 2θ=27.8° (100% peak). The excitation spectra of the SrMoO(4):Eu(3+) (λ(Em.)=614 nm) presented the characteristic band of the Eu(3+5)L(6) transition at 394 nm and a broad band at around 288 nm ascribed to the charge-transfer from the O (2p) state to the Mo (4d) one in the SrMoO(4) matrix. The emission spectra of the SrMoO(4):Eu(3+) powders (λ(Exc.)=394 and 288 nm) show the group of sharp emission bands among 523-554 nm and 578-699 nm, assigned to the (5)D(1)→(7)F(0,1 and 2) and (5)D(0)→(7)F(0,1,2,3 and 4), respectively. The band related to the (5)D(0)→(7)F(0) transition indicates the presence of Eu(3+) site without inversion center. This hypothesis is strengthened by the fact that the band referent to the (5)D(0)→(7)F(2) transition is the most intense in the emission spectra.

Europium(III) concentration effect on the spectroscopic and photoluminescent properties of BaMoO(4):Eu.

BaMoO(4):Eu (BEMO) powders were synthesized by the polymeric precursor method (PPM), heat treated at 800 degrees C for 2 h in a heating rate of 5 degrees C/min and characterized by powder X-ray diffraction patterns (XRD), Fourier Transform Infra-Red (FTIR) and Raman spectroscopy, besides room temperature Photoluminescence (PL) measurements. The emission spectra of BEMO samples under excitation of 394 nm present the characteristic Eu(3+) transitions. The relative intensities of the Eu(3+) emissions increase as the concentration of this ion increases from 0.01 to 0.075 mol, but the luminescence is drastically quenched for the Ba(0.855)Eu(0.145)MoO(4) sample. The one exponential decay curves of the Eu(3+ 5)D(0)-->(7)F(2) transition, lambda (exc) = 394 nm and lambda (em) = 614 nm, provided the decay times of around 0.54 ms for all samples. It was observed a broadening of the Bragg reflections and Raman bands when the Eu(+3) concentration increases as a consequence of a more disordered material. The presence of MoO(3) and Eu(2)Mo(2)O(7) as additional phases in the BEMO samples where observed when the Eu(3+) concentration was 14.5 mol%.

Effect of the order and disorder of BaMoO4 powders in photoluminescent properties.

The study of the photoluminescent properties affected by order and disorder of the BaMoO(4) powders is the principal objective in this work. BaMoO(4) compounds were prepared using soft chemical process called Complex Polymerization Method. In this work, different deagglomeration types and different heating rates were used to promote different disorder degrees. Scheelite type phase (BaMoO(4)) was determined by X-ray Diffraction (XRD), Fourier Transformed Infra-Red (FTIR) and Raman spectroscopy after heat treating the sample at 400 degrees C. The room temperature luminescence spectra revealed an intense single-emission band in the visible region. Based on XRD and Raman data it was observed that the transition between the completely disordered structure to completely ordered structure is a good condition for photoluminescence (PL) emission. The best PL emission is obtained when the material possesses short range disorder, i.e., is periodically ordered (XRD), but some disorder as measured by Raman spectroscopy. The excellent optical properties observed for disordered BaMoO(4) suggested that this material is a highly promising candidate for optical applications.

Synthesis, characterization and photophysical properties of Eu3+ doped in BaMoO4.

In this work Ba(0.99)Eu(0.01)MoO(4) (BEMO) powders were prepared by the first time by the Complex Polymerization Method. The structural and optical properties of the BEMO powders were characterized by Fourier Transform Infra-Red (FTIR), X-ray Diffraction (XRD), Raman Spectra, High-Resolution Scanning Electron Microscopy (HR-SEM) and Photoluminescent Measurements. XRD show a crystalline scheelite-type phase after the heat treatment at temperatures greater than 400 degrees C. The ionic radius of Eu(3+) (0.109 nm) is lower than the Ba(2+) (0.149 nm) one. This difference is responsible for the decrease in the lattice parameters of the BEMO compared to the pure BaMoO(4) matrix. This little difference in the lattice parameters show that Eu(3+) is expected to occupy the Ba(2+) site at different temperatures, stayed the tetragonal (S(4)) symmetry characteristic of scheelite-type crystalline structures of BaMoO(4). The emission spectra of the samples, when excited at 394 nm, presented the (5)D(1)-->(7)F(0, 1 and 2) and (5)D(0)-->(7)F(0, 1, 2, 3 and 4) Eu(3+) transitions at 523, 533, 554, 578, 589, 614, 652 and 699 nm, respectively. The emission spectra of the powders heat-treated at 800 and 900 degrees C showed a marked increase in its intensities compared to the materials heat-treated from 400 to 700 degrees C. The decay times for the sample were evaluated and all of them presented the average value of 0.61 ms. Eu(3+) luminescence decay time follows one exponential curve indicating the presence of only one type of Eu(3+) symmetry site.