Renato B. Guimarães

Spectroscopic analysis of Eu3+ -and Eu3+:Yb3+-doped yttrium silicate crystalline powders prepared by combustion synthesis

Yttrium silicate powders doped with Eu3+ and codoped with Eu3+ and Yb3+ were prepared by combustion synthesis. The x-ray powder diffraction data showed the presence of Y2SiO5 and Y2Si2O7 crystalline phases. Singly doped (1 wt %) sample illuminated with ultraviolet light (λ=256 nm) showed the characteristic red luminescence corresponding to D50→F7J transitions of Eu3+. The Judd–Ofelt intensity parameters were calculated from experimental data and the radiative and nonradiative relaxation rates were estimated. The results showed that the nonradiative relaxation rate is smaller in yttrium silicate compared to yttrium oxide powder, a reference material, prepared under similar conditions. Codoped samples were exposed to near-infrared laser excitation (λ=975 nm) and the red luminescence of Eu3+ was also observed. In this case, the luminescence is achieved due to a cooperative upconversion (CUC) process involving energy transfer (ET) from pairs of ytterbium ions to europium ions. The ET rate was estimated by fit...

Experimental observation of quantum entanglement in low-dimensional spin systems

We report macroscopic magnetic measurements carried out in order to detect and characterize field-induced quantum entanglement in low-dimensional spin systems. We analyze the pyroborate

Magnetism and charge ordering in Fe 3 O 2 BO 3 studied by Fe 57 Mössbauer spectroscopy

\mathrm{Mg}\mathrm{Mn}{\mathrm{B}}_{2}{\mathrm{O}}_{5}

Structural and spectroscopic analyses of europium doped yttrium oxyfluoride powders prepared by combustion synthesis

and the warwickite

Magnetic and transport properties of low-dimensional oxi-borates

\mathrm{Mg}\mathrm{Ti}\mathrm{O}\mathrm{B}{\mathrm{O}}_{3}

Strongly disordered Heisenberg spin-1 chains : vanadium warwickites

, systems with spin

Magnetic properties of Fe–Cu alloys prepared by pulsed electrodeposition

5∕2

Thermal stability and diffusion studies in the Au and Bi implanted AZ1350 photoresist

and

Three- and four-photon excited upconversion luminescence in terbium doped lutetium silicate powders by femtosecond laser irradiation

1∕2

Guanidine-functionalized Fe3O4 magnetic nanoparticles as basic recyclable catalysts for biodiesel production

, respectively. By using the magnetic susceptibility as an entanglement witness we are able to quantify entanglement as a function of temperature and magnetic field. In addition, we experimentally distinguish a system exhibiting a random singlet-phase state from one with the Griffiths phase. This analysis opens the possibility of a more detailed characterization of low-dimensional materials.