Eu3+ doped high-aluminum cast residue prepared EuCaAl3O7/Ca2Al2SiO7 luminescent material with 5D0→7F2/5D0→7F4 double red intense emission

Sr2Al2SiO7 (SAS) phosphors doped with Eu3+, Ce3+, Ce3+/Eu3+ ions were synthesized by solid-state reaction heating at 1250°C. The phonon energy associated with the 7F0 → 5D2 transition of Eu3+ ions in SAS material was determined by phonon sideband spectra, and vibration energies in the 200–1200 cm−1 region were measured from the Raman spectra. The asymmetry of the Eu3+ site in the SAS lattice was estimated by the Judd–Ofelt intensity parameters analysis. Ωλ (λ = 2, 4, 6) intensity parameters determined from emission spectra showed that the introducing of Al2O3 leads to an enhancement of the asymmetry of the Eu3+ surroundings in SAS:Eu3+ materials. Photoluminescence investigation of SAS:Ce3+ (x mol%),Eu3+ (1 mol%) (x = 0, 0.5, 1.0, and 1.5) samples indicated that there is an energy transfer from the sensitizer Ce3+ to the activator Eu3+ in the Sr2Al2SiO7 host lattice.

Judd–Ofelt Parameters of Eu3+ and Energy Transfer of Ce3+/Eu3+ in Sr2Al2SiO7 Materials

Abstract Bi-doped CaO–Al2O3–SiO2 glass microspheres with Ca2Al2SiO7 (gehlenite) composition were prepared by combination of solid-state reaction and flame synthesis. The concentration of Bi was 0.0, 0.5, 1 and 3 mol%. The chemical composition of prepared glass microspheres was determined by X-ray fluorescence (XRF). The structural and magnetic properties of prepared glass microspheres and their polycrystalline analogues were studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Raman spectroscopy and SQUID magnetometry. The closer inspection of glass microspheres surface by SEM confirmed smooth surface and revealed no features indicating presence of crystalline phases. All Bi-doped microspheres are X-ray amorphous, however in case of undoped microspheres XRD detected traces of crystalline gehlenite. XRD analysis of samples crystallized at 1273 K for 10 h revealed the presence of gehlenite as the main crystalline phase. The presence of gehlenite in crystallized samples were also confirmed by Raman spectroscopy. All samples (glass microspheres and their crystalline analogues) showed diamagnetic or weak ferromagnetic behavior at room temperature, whereas paramagnetic or weak ferromagnetic behavior was observed at 2 K.

Structure and magnetic properties of Bi-doped calcium aluminosilicate glass microspheres

The remote phosphor configuration, though not the best choice for WLED color quality, is superior to the luminous flux of LEDs compared to the conformal or in-cup structures. Realizing the capability of the remote phosphor design, several studies have been done to overcome the drawback of this structure, which is the color quality. A two-film distant phosphor configuration with improved color rendering index (CRI) and color quality ratio (CQS) for WLEDs is offered in this study paper. The hue temperature of the WLEDs packets employed in this research is 8500 K. This phosphor structure is constructed by layering of a green CaS:Sb3+,Na or red ZnS:Sn2+ phosphor above the yellow YAG:Ce3+ phosphor. The additional phosphor ZnS:Sn2+ concentration will then be modified to get the best color quality. The results demonstrated an increase in CRI and CQS along with the presence of ZnS:Sn2+, indicating that the existence of ZnS:Sn2+ influences significantly on these two aspects. As a result of the increased concentration of red illumination elements inside packets, the higher the concentration of ZnS:Sn2+, the higher the CRI and CQS. The green phosphor CaS:Sb3+,Na, in the meantime, improves the luminous flux.

CaS: Sb3+, Na and ZnS:Sn2+: phosphor materials for the improvement of WLEDs

Y3Al5O12:Ce3+ (YAG:Ce3+), the most common yellow phosphor for WLEDs, has a red insufficiency in its light spectrum. The Ce3+ spectral profile is modified in this research using surface-located ATTO-Rho101 dye molecules, which have powerful, wide impregnation in the greenish-yellow spectroscopic zone of Ce3+ radiation and vivid red-emitting radiation. To create a spherical shell and evenly dispersed micro and nanometer YAG:Ce3+, a modified solvothermal technique is applied. Surface SiO2 covering and synchronized dye embedding are accomplished using solvothermally generated YAG:Ce3+, temperature-stimulated micro-YAG:Ce3+, plus commercialized phosphorus. Upon blue light excitation, the accumulated YAG:Ce3+@SiO2+dye powder exhibits efficient radiative conversion/reintake from Ce3+ within the internal structure of YAG to the pigment particles from the SiO2 external shell, despite the phosphors' diameter; which likely boosts its red radiation. Fluorescence microscopy would be a suitable way to determine the reabsorption of powdered substances.

The qualities of dyed YAG:Ce3+@SiO2 for WLEDs via energy conversion

Ca1.86Al2(Si1-xMox)O7:0.14Eu3+ and Ca1.86Al2Si1+yO7+2y:0.14 Eu3+ were synthesized by solid-state reaction. X-ray powder diffraction, excitation and emission spectra were used to investigate their structures and photoluminescence properties. The results shows that the phosphor Ca1.86Al2SiO7:0.14Eu3+ cannot be excited efficiently by light of 393 nm. The introduced Mo ion does not change the position of the excitation peak, but increases both the absorption at 400nm and the emission intensity of Eu3+. The intense red emitting phosphor Ca1.86Al2(Si0.95Mo0.05)O7:0.14Eu3+ was obtained, which has 67% enhanced luminous intensity compared to that of the undoped sample Ca1.86Al2SiO7:0.14Eu3+. Otherwise, SiO2 excess of non-stoichiometric phosphors Ca1.86Al2Si1+yO7+2y:0.14Eu3+ showed the characteristic pattern of a tetragonal structure with a small SiO2 concentration. The optimal phosphor of Ca1.86Al2Si1.1O7.2:0.14Eu3+ has a luminous intensity about two times higher than that of the original stoichiometric phosphor Ca1.86Al2SiO7:0.14Eu3+. We confirmed that the photoluminescence intensity of the obtained phosphors is fairly enhanced by excessive SiO2. The mechanism of this photoluminescence enhancement is discussed in this paper.

https://iopscience.iop.org/article/10.1088/1757-899X/292/1/012058/pdf

Enhancement of red emission intensity of Ca2Al2SiO7:Eu3+ phosphor by MoO3 doping or excess SiO2 addition for application to white LEDs

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Enhancement of red emission intensity of Ca2Al2SiO7:Eu3+ phosphor by MoO3 doping or excess SiO2 addition for application to white LEDs