Europium doped thiosilicate phosphors of the alkaline earth metals Mg, Ca, Sr and Ba: Structure and luminescence (original) (raw)
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Structure and luminescence of (Ca,Sr) 2 SiS 4 : Eu 2+ phosphors
Journal of Physics D: Applied Physics, 2010
Sr 2 SiS 4 :Eu 2+ , Ca 2 SiS 4 :Eu 2+ and the solid solution of both, europium-doped (Ca,Sr) 2 SiS 4 , were investigated as UV-VIS excitable green to red powder phosphors. Sr 2 SiS 4 :Eu 2+ shows two emission bands, peaking at 480 nm and 550 nm. By changing the ratio between Ca 2+ and Sr 2+ , the photoluminescent emission spectrum can be tuned. Using X-ray diffraction, the phase composition and lattice parameters of the thiosilicate compounds were determined. The material forms a single, monoclinic Sr 2 SiS 4 -like phase up to 40% substitution of Sr 2+ by Ca 2+ . From 50% to 90% of substitution by Ca 2+ , phase separation was observed, leading to more complex emission spectra.
A XAS study of the luminescent Eu centers in thiosilicate phosphors
Physical Chemistry Chemical Physics, 2013
Due to its bright yellow-to-red emission, europium doped Ca 2 SiS 4 is a very interesting material for phosphor converted light emitting diodes. The emission spectrum is highly dependent on the Eu concentration and can consist of more than one emission band. We combined X-ray absorption fine structure and photoluminescence measurements to analyze the structure of europium centers in (Ca,Eu) 2 SiS 4 luminescent powders. This paper provides an explanation for the concentration dependency of the emission spectra. We find that at low dopant concentrations a large fraction of trivalent europium ions is unexpectedly present in the powders. These trivalent europium ions tend to form defect clusters in the luminescent powders.
ACS Applied Materials & Interfaces, 2014
A new Ce 3+-activated thiosilicate phosphor, BaLa 2 Si 2 S 8 :Ce 3+ , was synthesized by using solid-state methods in a fused silica ampule and found to crystallize in the structure type of La 2 PbSi 2 S 8. The crystal structure has been characterized by synchrotron X-ray diffraction and refined with Rietveld methods. This novel cyan-emitting phosphor can be excited over a broad range from UV to blue light (380−450 nm) and generates a broadband emission peaking at 471 nm with a quantum efficiency of 36%. Nonradiative transitions between Ce 3+ ions in BaLa 2 Si 2 S 8 :Ce 3+ have also been demonstrated to be attributable to dipole−dipole interactions, and the critical distance was calculated to be 17.41 Å. When BaLa 2 Si 2 S 8 :Ce 3+ phosphor was utilized to incorporate with yellow-emitting (Sr,Ca) 2 SiO 4 :Eu 2+ phosphor and red-emitting CaAlSiN 3 :Eu 2+ phosphor on a 430 nm blue LED chip, a warm white light LED device with color rendering index of ∼96 was obtained. The results indicate that cyan-emitting BaLa 2 Si 2 S 8 :Ce 3+ can serve as a potential phosphor for incorporation in fabrication of solid-state lighting. The preparation, spectroscopic characterization, quantum efficiency, decay lifetime, thermalquenching behavior, and related LED device data are also presented.
Structure and photoluminescence of (Ca,Eu) 2 SiS 4 powders
Journal of Physics: Condensed Matter, 2007
The photoluminescence of Ca 2 SiS 4 :Eu powders was investigated in detail as a function of europium concentration (from 0.1% Ca substitution to the fully substituted Eu 2 SiS 4 ). At low europium dopant concentration (<10%) the powders crystallize in an orthorhombic structure and the emission spectrum is dominated by two broad emission bands, at 564 and 660 nm. The emission can be tuned from yellow (CIE x = 0.46, y = 0.53) to red (CIE x = 0.65, y = 0.35) by variation of the Eu concentration. An energetic coupling exists between both bands, leading to a broad excitation wavelength range. Powders with high europium concentration (>40%) crystallize in a monoclinic structure, details of which were determined by Rietveld refinement of x-ray diffraction data. For the composition CaEuSiS 4 (i.e. 50% substitution), the luminescence peaks at 614 nm, shifting to shorter wavelengths upon further substitution of Ca by Eu. Although considerable thermal quenching is present at room temperature in the fully Eu-substituted compound, Eu 2 SiS 4 is still photoluminescent, with a peak emission wavelength of 577 nm. A strong correlation is found between the crystallographic and luminescent properties of the (Ca, Eu) 2 SiS 4 powders. The broad emission and excitation bands make this phosphor a good candidate for use in phosphor-converted light-emitting diodes (pcLEDs).
Luminescence : the journal of biological and chemical luminescence, 2015
A europium (Eu)-doped di-calcium magnesium di-silicate phosphor, Ca2 MgSi2 O7 :Eu(2+) , was prepared using a solid-state reaction method. The phase structure, particle size, surface morphology, elemental analysis, different stretching mode and luminescence properties were analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) with energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, photoluminescence (PL) and mechanoluminescence (ML). The phase structure of Ca2 MgSi2 O7 :Eu(2+) was an akermanite-type structure, which belongs to the tetragonal crystallography with space group P4̅21 m; this structure is a member of the melilite group and forms a layered compound. The surface of the prepared phosphor was not found to be uniform and particle distribution was in the nanometer range. EDX and FTIR confirm the components of Eu(2+) -doped Ca2 MgSi2 O7 phosphor. Under UV excitation...
Journal of Radiation Research and Applied Sciences, 2015
Europium doped di-strontium magnesium di-silicate phosphor namely (Sr 2 MgSi 2 O 7 :Eu 3þ) was prepared by the traditional high temperature solid state reaction method. The phase structure of sintered phosphor was akermanite type structure which belongs to the tetragonal crystallography with space group P42 1 m, this structure is a member of the melilite group and forms a layered compound. The EDX and FTIR spectra confirm the present elements in Sr 2 MgSi 2 O 7 :Eu 3þ phosphor. Photoluminescence measurements showed that the phosphor exhibited strong emission peak with good intensity, corresponding to 5 D 0 / 7 F 2 (613 nm) red emission and weak 5 D 0 / 7 F 1 (590 nm) orange emission. The excitation spectra monitored at 613 nm show broad band from 220 to 300 nm ascribed to OeEu charge-transfer band (CTB) centered at about 269 nm, and the other peaks in the range of 300e400 nm originated from fef transitions of Eu 3+ ions. The strongest band at 395 nm can be assigned to 7 F 0 / 5 L 6 transition of Eu 3þ ions due to the typical fef transitions within Eu 3þ of 4f 6 configuration.
Research on Chemical Intermediates, 2014
Sr 2 MgSi 2 O 7 :Eu 2? , Dy 3? and Ca 2 MgSi 2 O 7 :Eu 2? , Dy 3? phosphors were synthesized by the high-temperature solid-state reaction method. The phase structure of the prepared phosphors was of akermanite type, which belongs to the tetragonal crystallography. The EDX and FTIR spectra confirm the presence of elements in prepared phosphors. Sr 2 MgSi 2 O 7 :Eu 2? , Dy 3? and Ca 2 MgSi 2 O 7 :Eu 2? , Dy 3? phosphors would emit blue and green light; the main emission peaks that appeared at 465 and 535 nm belong to the broad emission band ascribed to the 4f 6 5d 1 ? 4f 7 transition. Decay graph indicates that both the phosphors have fast decay and slow decay. Investigation into afterglow property showed that the Sr 2-MgSi 2 O 7 :Eu 2? , Dy 3? phosphor held better afterglow property than Ca 2 MgSi 2 O 7 :-Eu 2? , Dy 3? phosphors. ML measurements showed a linear increase in the ML intensity with the impact velocity of the moving piston.
Luminescence Properties of Sr2MgSi2O7:Eu2+, Ce3+ Phosphor by Solid State Reaction Method
Physics Procedia, 2015
The Sr 2 MgSi 2 O 7 :Eu 2+ , Ce 3+ phosphor was prepared by solid state reaction method, boric acid (H 3 BO 3) was added as flux. The phase structure of Sr 2 MgSi 2 O 7 :Eu 2+ , Ce 3+ phosphor was akermanite type structure which belongs to the tetragonal crystallography with space group P4̅ 2 1 m, this structure is a member of the melilite group and forms layered compound. EDX and FTIR spectra confirm the present elements in Sr 2 MgSi 2 O 7 :Eu 2+ , Ce 3+ phosphor. Three peaks in excitation spectra were found at 253, 293, 325nm and corresponding emission peak was recorded at 465nm, belonging to the broad emission ascribed to the 4f 6 5d 1 →4f 7 transition of Eu 2+. The ML intensity of prepared phosphor was increasing linearly with increases of mechanical load.
Materials Science and Engineering: B, 2008
Rare earth doped thiosilicates are promising materials for use in phosphor converted light emitting diodes (pcLEDs). These phosphors (including the hosts Ca 2 SiS 4 , BaSi 2 S 5 and Ba 2 SiS 4 in combination with Ce 3+ and/or Eu 2+ doping) cover the entire visible part of the spectrum, as the emission colour can be changed from deep blue to red. The photoluminescence emission spectrum and the overlap of the excitation spectrum with the emission of pumping LEDs is evaluated. The trade-off between high colour rendering and high electrical-to-optical power efficiency is discussed by simulation with both blue and UV emitting LEDs. Finally, a phosphor combination with low colour temperature (3000 K) and high colour rendering (CRI = 93) is proposed.
Luminescence of Cesium Thiocyanate (CsSCN) doped with Eu 2+ (CsSCN:Eu 2+ )
Many host lattices have been investigated, as it is known that the effect of the host lattice in luminescence is complex, therefore this work seek to investigate Cesium Thiocyanate (CsSCN) as a suitable host lattice in luminescence. Cesium Thiocyanate is doped with EU 2+ and the Luminescence of the doped compound measured. CsSCN was prepared from Cd(SCN) 2 and Ca(CO) 3 . The prepared CsSCN was then doped with 0.05% EU 2+ at 220 oc . The Luminescence spectra of the CsSCN:EU 2+ was measured using a D5000diffractometer. The emission spectra obtained is broad with the maximum at 19801cm -1 . The spectra obtained were in agreement with typical thiocynante spectra that were doped with EU 2+ . CsSCN can therefore be used as a host lattice with some minor problems of decomposition by products.