Evaluation of photonic properties of photolinescent material based on Er3+/Yb3+/Eu3+ tri doped SiO2 and Gd2O3 for energy conversion

This work reports the preparation, structural and spectroscopic characterization of the SiO2-Gd2O3:Er3+/Yb3+/Eu3+ materials. The materials were successfully obtained by the sol-gel method after heat treatment at 900 °C/ 8 h. The XRD and Rietveld refinement data indicated the formation of the cubic structure of Gd2O3 with spatial group Ia3 (206); the undoped sample also showed the formation of 8.24% of the monoclinic phase (C2/m). Infrared spectroscopy results confirmed the formation of SiO2 and Gd2O3 as well as the presence of dopants in the matrix. SEM micrographs indicated a system in which Gd2O3 are dispersed in SiO2. The EDS analysis showed peaks related to Si, Gd, O, in addition to Er, Yb and Eu, confirming the doping. The excitation spectra showed similar profiles, with bands assigned to transitions 8S7/2 → 6DJ and 8S7/2 → 6IJ of the Gd3+ ion, intraconfigurational 4f – 4f 5D0 → 7FJ (J: 0 – 4) of Eu3+ transitions and 4I15/2 → 4F7/2 of Er3+ ion, in addition to the O2-(2p) → Eu3+(4f6) charge transfer band. In the downconversion process, bands related to the transitions 5D0 → 7FJ (J: 0 – 4) of the Eu3+ ion, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 (Er3+) were observed. The 5D0 excited state lifetimes were calculated for all samples at different excitation wavelengths. The material SGEYE1 presented the highest lifetime value of 2.987 ms, suggesting that the tri-doped with Er3+, Yb3+ and 1.0 mol% of Eu3+ sample is the best concentration of Eu3+ for the SiO2-Gd2O3 system. In the upconversion process, bands were observed in all spectra related to 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ion. Based on the best results of downconversion and upconversion, the SGEYE1 material was subjected to luminescence spectroscopy under simultaneous excitation at 247.50 and 980.00 nm. Both DC and UC phenomena were noted simultaneously with the presence of emission bands related to 5D0 → 7FJ (J: 0 – 4) transitions of Eu3+ ion, and 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ion.CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorCNPq - Conselho Nacional de Desenvolvimento Científico e TecnológicoFAPEMIG - Fundação de Amparo a Pesquisa do Estado de Minas GeraisFAPESP - Fundação de Amparo a Pesquisa do Estado de São PauloFinep - Financiadora de Estudos e ProjetosUFU - Universidade Federal de UberlândiaDissertação (Mestrado)Neste trabalho foram realizadas a preparação, caracterização estrutural e espectroscópica dos materiais SiO2-Gd2O3:Er3+/Yb3+/Eu3+. Os materiais foram obtidos pelo método sol-gel sucedido de tratamento térmico a 900 °C/8 h. Os dados de DRX e refinamento de Rietveld indicaram a formação da estrutura cúbica do Gd2O3 com grupo espacial Ia3 (206), sendo que o material não dopado apresentou também a formação de 8,24% da fase monoclínica (C2/m). Os resultados de espectroscopia de infravermelho confirmaram a formação do SiO2 e Gd2O3 bem como a presença dos dopantes na matriz. A análise de MEV indicou a morfologia em que partículas de Gd2O3 são formadas dentro do SiO2. Nos espectros de EDX foram observadas bandas atribuídas à Si, Gd, O, além de Er, Yb e Eu, confirmando a presença dos dopantes nos materiais. Os espectros de excitação apresentaram perfis semelhantes, com bandas relacionadas às transições 8S7/2 → 6DJ e 8S7/2 → 6IJ do íon Gd3+, intraconfiguracionais 4f–4f do íon Eu3+ e 4I15/2 → 4F7/2 do íon Er3+, além da banda de transferência de carga O2-(2p) → Eu3+(4f6). No processo de downconversion, foram observadas bandas designadas às transições 5D0 → 7FJ (J: 0 – 4) do íon Eu3+, 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 e 4F9/2 → 4I15/2 do íon Er3+. Foram obtidos os tempos de vida do estado excitado 5D0. O maior valor de tempo de vida, 2,987 ms para o material SGEYE1, sugere que o material triplamente dopado com Er3+, Yb3+ e 1,0 % em mol de Eu3+ é a concentração ideal de Eu3+. No processo de upconversion, em todos os espectros foram observadas bandas atribuidas às transições 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 e 4F9/2 → 4I15/2 do íon Er3+. Com base nos melhores resultados de fotoluminescência, o material SGEYE1 foi submetido à espectroscopia de luminescência sob excitação simultânea em 247,50 e 980,00 nm. Observou-se os processos de downconversion e upconversion simultaneamente devido ao aparecimento de bandas de emissão relacionadas com as transições 5D0 → 7FJ (J: 0 – 4) do íon Eu3+, e 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 e 4F9/2 → 4I15/2 do íon Er3+

Efficient Ni and Fe doping process in ZnO with enhanced photocatalytic activity: A theoretical and experimental investigation

Zn1-xNixO and Zn1-xFexO structures were synthesized by the microwave-assisted hydrothermal method. The best photocatalytic degradation of rhodamine B (RhB) and 4-nitrophenol (4-NP) were achieved by the Zn0.96Ni0.04O and Zn0.99Fe0.01O. The specificity of each dopant showed significance in the positions of the impurity energy levels, which ended up influencing the electron-hole separation and transport, as demonstrated by the photoluminescence emissions. The morphological analysis revealed that besides inhibiting the growth of particles, the incorporation of dopant ions into the ZnO lattice triggered a nucleation process, consequently changing their morphology. Density functional theory (DFT) calculations showed that the Fe3+ 3d orbitals generate energy levels below the conduction band (CB) while for Ni2+, the levels were found to be spread in a broad energy range above the valence band (VB). The synergistic effect of band gaps alteration, inhibition of electron-hole pair recombination and appearance of new trapping energy sites justifies the superior photocatalytic activity

Detection of SARS-CoV-2 RNA on public surfaces in a densely populated urban area of Brazil: a potential tool for monitoring the circulation of infected patients

The world is experiencing the worst global health crisis in recent decades since December/2019 due to a new pandemic coronavirus. The COVID-19 disease, caused by SARS-CoV-2, has resulted in more than 30 million cases and 950 thousand deaths worldwide as of September 21, 2020. Determining the extent of the virus on public surfaces is critical for understanding the potential risk of infection in these areas. In this study, we investigated the presence of SARS-CoV-2 RNA on public surfaces in a densely populated urban area in Brazil. Forty-nine of 933 samples tested positive (5.25%) for SARS-CoV-2 RNA, including samples collected from distinct material surfaces, including metal and concrete, and distinct places, mainly around hospital care units and public squares. Our data indicated the contamination of public surfaces by SARS-CoV-2, suggesting the circulation of infected patients and the risk of infection for the population. Constant monitoring of the virus in urban areas is required as a strategy to fight the pandemic and prevent further infections

Núcleos de Ensino da Unesp: artigos 2008

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq