Structure-property relations of inorganic luminescent materials obtained by microwave-assisted synthesis method

Abstract

Energy-converters inorganic materials are in full development and have fundamental importance in modern society in the form of solar cells, optical batteries, LEDs for lighting, digital memory storage devices, etc.Since the mid-1990s, these inorganic materials have played a key role in emerging solid state lighting (SSL) technology. PC-LED (phosphor converting lighting emitting diode) is a combination of a LED (emitting diode) emitting in near or blue UV and a phosphor that absorbs this radiation and emits at longer wavelengths (green, yellow and red etc.)The current challenge is the development of luminescent materials activated by solar radiation, which have application from emergency lighting to diagnosis of diseases and tumors.Moreover, in the current economic situation, energy-efficient synthesis alternatives, coupled with low-cost materials, are extremely necessary to ensure that the processes are sustainable. The use of inexpensive and abundant raw materials and new low-cost synthetic routes in obtaining high-quality phosphors, together with the application of solid-state lighting technology, can bring significant energy savings worldwide.The most commonly used phosphors for light conversion consist of inorganic materials derived from oxides, nitrides, oxynitrites, oxysulfides and fluorides, which are normally doped with rare earth ions (Ce3 + or Eu2 +). These ions have electronic configurations [Xe] 4f1 and [Xe] 4f7 for the cerium and europium ions, respectively. The emission colors of these ions are derived from interconfiguration transitions (4f5d) that can be tuned to appropriate regions of the visible spectrum and therefore strongly depend on the binding domain of the host matrix.Alternatively, other ions such as transition metals d (Ti, Mn, and Cr) have the potential to be applied as activators in phosphors due to their low cost, abundance and easy separation. The ions that particularly attract attention in the area of luminescence are the Ti, because it has broad band and tunable in the region of the visible, and the Mn because it has broad emission band in the red region.In this project will be developed new routes of obtaining luminescent materials for application in light energy conversion, among them: i) Microwave-assisted solid-state synthesis and ii) Conventional solid-state synthesis (ceramic method). In addition, the spectroscopic properties of luminescent materials will be investigated based on: i) In the study of the structure-property relations of the materials; Ii) the structure of the energy levels of the emitting ions involved, as well as energy transfer and migration processes; Iii) optical properties - lifetimes (t) and emission quantum yields (qexp). Finally, the project contemplates the manufacture of white light emitting devices with high quality phosphors, as well as the study of their photoluminescent properties.The mechanisms of inorganic reactions assisted by microwave radiation will be studied using ex-situ and in-situ analysis by means of X-ray diffraction technique, in order to correlate structural properties with luminescent efficiency. The photoluminescent processes of the obtained materials will also be analyzed in order to facilitate the design of new luminescent materials. (AU)