Eu 2þ or Cr 3þ singly doped and Eu 2þ -Cr 3þ co-doped MgSrAl 10 O 17 luminescent materials were synthesized by solid-state reactions and their photoluminescence properties were investigated. These luminescent materials have absorption in the UV-Vis region and give luminescence in the deep-red region ($693 nm), which are suitably applied in a device of luminescent solar concentrator (LSC) for improving the efficiency of silicon solar cells. In these luminescent materials, Eu 2þ located at Sr 2þ site can effectively transfer its absorbed energy to Cr 3þ at Al 3þ site. The energy transfer from Eu 2þ to Cr 3þ takes the dipole-dipole interaction mechanism. The transfer efficiency (g ET ) approaches about 0.63 and the optimized quantum efficiency (QE) for Cr 3þ emission is about 11%.Over past tens years, many attentions have been paid to the development of solar cells as promising devices for inexpensive and large-scale solar energy conversion. The efficiency in the commercial Si solar cells is just about 15%, which means that most of sunlight energy (over 70%) is lost. 1-3 The main energy loss for these cells in the conversion of solar energy to electricity is related to the so-called spectral mismatch between incident solar photon energies and the energy gap (E g ) of the cells. 4 As we know, the main energy of the solar emission dispersing on the earth surface is in visible light region, but E g of the Si cell ($1.1 eV) is suitable for the absorption in deep-red and near-infrared region.Nowadays, luminescent solar concentrator (LSC) has attracted research interest worldwide. LSC is a kind of unique and efficient device that can collect solar photons and transfer them to the photons matching E g of the Si solar cells. A typical LSC is constructed by a transparent waveguide plate coated with a luminescent material film and the Si solar cells are closely mounted at the edges of the plate. When luminescent materials with efficient UV-Vis absorption and deep-red and near-infrared emissions are applied in LSCs, the efficiency of Si cells would be significantly enhanced. Recently, Michael J. Currie et al. 5 reported a LSC constructed by organic luminescent materials. Normally, organic luminescent materials have high efficiency, but their stability is doubtable. If inorganic materials with efficient far-red and near-infrared emissions are developed, the stability of the LSCs will be improved, which will be significantly to enhance the efficiency of Si cells.As we know, Cr 3þ with red emission is one of the most used activators in laser crystals. 6 Recently, Ruixia Zhong et al. have reported the efficient energy transfer from Eu 2þ to Cr 3þ in Sr 4 Al 14 O 25 , 7 SrAl 12 O 19 nano-rods 8 and Sr 3 Al 10 SiO 20 -SrAl 12 O 19 mixed phases 9 , which were reportedly to be used for illumination and display. It may be deduced that Eu 2þ ÀCr 3þ co-doped luminescent materials may be used in LSC. In this paper, we report the photoluminescence characteristics of Eu 2þ or Cr 3þ singly doped and Eu 2þ ÀCr 3þ co-doped MgSrAl 12 O 19 and t...
NaSr 2 Nb 5 O 15 piezoelectric ceramics were sintered at different temperatures with or without atmospheric powder. The effects of atmospheric powder and sintering temperature on the dielectric, piezoelectric, and ferroelectric properties of the ceramics were analyzed. According to the modified Curie-Weiss law, we know that all these ceramics show an intermediate relaxor-like behavior between the normal and ideal relaxor ferroelectrics. Atmospheric powder affects significantly the properties of ceramics because the ceramics sintered without atmospheric powder lose lots of sodium. Furthermore, sintering temperature also significantly affects the properties of ceramics because the relative density of ceramics is enhanced when sintering temperature is increased.*
NaSr 2 Nb 5 O 15 lead-free piezoelectric ceramics were prepared by the sol-gel method; they were sintered at different temperatures with or without protective atmosphere. The influences of sintering temperature and protective atmosphere on the characterization and properties of the ceramics were investigated. All the ceramics showed the pure tungsten bronze structure and an intermediate relaxor-like behaviour between normal and ideal relaxor ferroelectrics according to the modified Curie-Weiss law. The sintering temperature affected significantly the properties of ceramics, with the sintering temperature increased both with and without protective atmosphere, the ε r , d 33 , K p and P r of these ceramics initially increased and decreased finally, whereas the variation of Q m and E c showed the opposite tendency. Furthermore, the protective atmosphere also significantly affected the properties of these ceramics, ε r , d 33 , K p and P r of such ceramics sintered with protective atmosphere were superior to those of the ceramics sintered without protective atmosphere, while the tan δ, Q m and E c gave the contrary results.
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