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Thermal sensing in NIR to visible upconversion of Ho3+ and Yb3+ doped yttrium o...
Jakka, S.K.; Soares, M.J.; Graça, M.P.F.; Neves, A.J.; Nagajyothi, P.C.; K, PavaniRare-earth (RE) oxyfluorides compatible for RE doping make a path for efficient near-infrared (NIR) to visible upconversion (UC). This paper describes the efficient use of YOF:Ho3+/Yb3+ phosphor nanoparticles synthesised by the Pechini sol-gel method as thermal sensors using UC in the visible region. Material characterisations such as X-ray diffraction, Raman spectroscopy and scanning electron microscopy (SEM),...
YAG:Ag nanophosphors – synthesis and characterization
Sundari, S. Shanmuga; Karthika, S.; Durairajan, A.; Graça, M.P.F.; Valente, M. A.Yttrium Aluminium Garnet (Y3Al5O12)-YAG and Ag of four different mol% in YAG (0.5, 1.0, 1.5 and 2.0 mol % of Ag) – YAG:Ag were synthesized by Pechini method. The synthesized pure YAG was white in colour but the incorporation of Ag in the YAG matrix forms colour centre and turns to pink. The intensity of pink Ag doped YAG is increasing with the increase in mol% of Ag. In the present work the synthesis and ...
Analogy of different optical temperature sensing techniques in LaNbO4:Er3+/Yb3+...
Pavani, K.; do Nascimento, J.P.C.; Jakka, S.K.; do Carmo, F.F.; Sales, A.J.M.; Soares, M.J.; Graça, M.P.F.; de Aquino, F.J.A.; Gouveia, D.X.Three of the possible approaches to optical temperature sensing of a thermographic phosphor were formally compared in upconversion (UC) of Er3+ and Yb3+ doped lanthanum orthoniobate (LNO) phosphor. The three approaches used in the study were namely fluorescence intensity ratio (FIR) of thermally coupled levels (TCL), Valley to Peak ratio (VPR) and the ratio of non-thermally coupled levels (NTCL), respectively. ...
Structural characterization of Brazilian niobium pentoxide and treatment to obt...
da Cruz, J.A.; Volnistem, E.A.; Ferreira, R.F.; Freitas, D.B.; Sales, A.J.M.; Costa, L.C.; Graça, M.P.F.Studies indicate that the degree of polymorphism of niobium pentoxide (Nb2O5) is related to the origin of its extraction and that adequate heat treatments can improve its quality concerning the number of structural phases. In this study, the niobium pentoxide extracted from the region of the Triângulo Mineiro in the state of Minas Gerais in Brazil was heat treated and its structural characterization reveals to ...
YAG:ag nanophosphors – synthesis and characterization
Sundari, S. Shanmuga; Karthika, S.; Durairajan, A.; Graça, M.P.F.; Valente, M.A.Yttrium Aluminium Garnet (Y3Al5O12)-YAG and Ag of four different mol% in YAG (0.5, 1.0, 1.5 and 2.0 mol % of Ag) – YAG:Ag were synthesized by Pechini method. The synthesized pure YAG was white in colour but the incorporation of Ag in the YAG matrix forms colour centre and turns to pink. The intensity of pink Ag doped YAG is increasing with the increase in mol% of Ag. In the present work the synthesis and the pr...
Impact of the pulling rate on the redox state and magnetic domains of Fe-Si-O g...
Salehizadeh, S.A.; Ferreira, N.M.; Ivanov, M.S.; Khomchenko, V.A.; Paixão, J.A.; Costa, F.M.; Valente, M.A.; Graça, M.P.F.This work studies the effect of the pulling rate, varying from 100 to 400 mm/h, on the redox state, structure and magnetic properties of iron oxide bearing silica glasses processed by laser floating zone (LFZ) method. XRD analysis revealed that the maximum crystallinity is obtained in the fibre grown at the lowest pulling rate. A detailed Raman analysis demonstrated that the global content of Fe2+ increases wit...
Sharp photoluminescence of Pr3+ ions in yttrium oxyfluoride nanospheres: thermo...
Suresh Kumar, J.; Pavani, K.; Graça, M.P.F.; Soares, M.J.YOF:Pr nanoparticles prepared by Pechni sol-gel method were investigated for temperature sensing in this work. Structural investigation such as XRD, Raman, SEM and EDS were done. Photoluminescence experiments at ambient temperature for three different concentrations and with variation in temperature were performed for application in fluorescence intensity ratio (FIR) technique. The FIR of the thermally coupled ...
Investigating the structural, morphological, dielectric and electric properties...
Issaoui, H.; Benali, A.; Bejar, M.; Dhahri, E.; Graça, M.P.F.; Valente, M.A.; Costa, B.F.O.The (La0.8Ca0.2)0.9Bi0.1FeO3 (LCBFO) compound has been synthesized by the sol-gel method and characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Raman spectroscopy and electrical impedance spectrometry. XRD results revealed that (La0.8Ca0.2)0.9Bi0.1FeO3 crystals are orthorhombic, belonging to the Pnma space group. The SEM measurements showed that the sample presents a large distributio...
Oxygen-vacancy-related giant permittivity and ethanol sensing response in SrTiO...
Trabelsi, H.; Bejar, M.; Dhahri, E.; Valente, M.A.; Graça, M.P.F.The ethanol sensing properties of SrTiO3-δ (δ = 0.075 and 0.125) ceramics was analyzed by dielectric measurements. The ceramics were prepared by solid state reaction method followed by the creation of oxygen vacancies-δ, through a thermal activated process. The crystal symmetry, space group and unit cell dimensions were derived from the X-ray diffraction (XRD) data using FullProf software whereas grain's size d...
Modulation of magnetism and study of impedance and alternating current conducti...
Amor, S.B.; Benali, A.; Bejar, M.; Dhahri, E.; Khirouni, K.; Valente, M.A.; Graça, M.P.F.; Al-Turjman, F.; Rodriguez, J.; Radwan, A.A spinel ferrite sample Zn0.4Ni0.6Fe2O4 was prepared by a conventional solid-state reaction method at high temperature. This compound was found to exhibit a single phase and crystallize in a cubic structure with Pm3 m Space group. The complex impedance was investigated in the temperature range 400–700 K and in the frequency range 100 Hz - 1 MHz. The Z-impedance analysis revealed that the relaxation phenomenon i...