Síntese e caracterização da matriz Nb2O5:La3+ , Eu3+ , obtida pelo processo sol-gel não-hidrolítico

• Autor(a) principal: Matias, Carlos Roberto
• Data de Publicação: 2014
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório do Centro Universitário Braz Cubas
• Texto Completo: https://repositorio.cruzeirodosul.edu.br/handle/123456789/1031
• topic: Diodos Emissores de Luz; Sol-Gel Não-hidrolítico; Óxido de nióbio; Luminescência; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA

Light Emitting Diode (LED) is an important strategy for solid-state lighting, for generation of white light from blue, green and red phosphors (RGB). Sulfide-based red-emitting phosphors are the most commonly used, but are chemically unstable and inefficient. Therefore, it is important to find a new source of phosphor which can emit intense red light absorbing energy in the near ultraviolet spectral region. Considering that luminescence characteristics, such as radiative lifetime, quantum efficiency of emission, emission intensity and color purity depend on the chemical environment surrounding the lanthanide ion, the non-hydrolytic sol-gel method using ethanol as the oxygen donor is presented as a good alternative for producing high-purity materials, fewer pores, a greater homogeneity and less formation of OH groups, which are effective deactivater for relaxation nonradiative. Thus, the present study aimed to the preparation and characterization of arrays of Nb2O5:La3+ , Eu3+ from the non-hydrolytic sol-gel process (NHSGP). To achieve the objectives arrays with different percentages of doping elements La3+ e Eu3+ were synthesized. In order to increase the energy transfer to the activator ions Eu3 +, some specimens were also doped with Bi3 +. The arrays were obtained from NHSGP method, having metal chlorides as precursors. Like the quantum efficiency of the emission from the state 5D0 to Eu3+ is dependent of the chemical environment around the ion emitter, the samples were subjected to heat treatment at different temperatures and times, aiming structural changes. The spectroscopic properties and structural characteristics of the samples in function of the composition and calcining temperature were evaluated. Diffraction patterns of X-rays of the arrays indicated that La3+, Eu3+ e/ou Bi3+ ions incorporated in the material did not change the structure of the matrix and the thermal treatment afforded different phases Nb2O5. Fluorescence assays indicated strong emission in the red for excitations at 276, 394, 465 and 525 nm. All samples showed the transitions characteristics of state 5D0 to Eu3+: 5D0→7 F(0,1,2,3,4), with more intense emission around 614 nm. Samples treated at 900 and 1200 ° C showed an anormal intensity of 7 F4 transition around 700 nm. Almost all the samples had values for chromaticity indices equal or slightly superior to the CIE defined by the National Television System Committee (NTSC). Higher heat treatment temperatures lead to smaller values for the wave widths at half height (FWHM) of the order 3 to 4 nm. Higher emission quantum efficiencies were observed for samples treated at 550 °C. Minor amounts of Eu3+ also resulted in higher quantum efficiency of emission. The material showed intense red emission for excitation at 276 nm. Such characteristic enables it to be a good candidate for be used in fluorescent lamps, replacing the red sulfide-based emitter. The material also showed intense emission in red for excitation at 394, 465 and 525 nm, indicating the possibility of its use as a red emitter in the composition of trichromatic LEDs, it can be excited by the energy of the blue emission at 455 nm emitter, and also the issue of energy green emitter at 520 nm. Addition of bismuth, contrary to what was expected, resulted in decrease in the value of the optical properties of the material. It is concluded that the developed material has potential for application both as a substitute for red phosphors currently used, and for application as red emitter in LEDs. Keywords: Sol-Gel Non-hydrolytic; Niobium oxide; Light Emitting Diodes; Luminescence.