Abstract
KMeY(PO4)2:5% Eu3+ phosphates have been synthesized by a novel hydrothermal method. Spectroscopic, structural, and morphological properties of the obtained samples were investigated by X-ray, TEM, Raman, infrared, absorption, and luminescence studies. The microscopic analysis of the obtained samples showed that the mean diameter of synthesized crystals was about 15 nm. The KCaY(PO4)2 and KSrY(PO4)2 compounds were isostructural and they crystallized in a rhabdophane-type hexagonal structure with the unit-cell parameters a = b ≈ 6.90 Å, c ≈ 6.34 Å, and a = b ≈ 7.00 Å, c ≈ 6.42 Å for the Ca and Sr compound, respectively. Spectroscopic investigations showed intense 5D0 → 7F4 transitions connected with D2 site symmetry of Eu3+ ions. Furthermore, for the sample annealed at 500 °C, europium ions were located in two optical sites, on the surface of grains and in the bulk. Thermal treatment of powders at high temperature provided better grain crystallinity and only one position of dopant in the crystalline structure. The most intense emission was possessed by the KSrY(PO4)2:5% Eu3+ sample calcinated at 500 °C.
Highlights
white-light-emitting diodes (W-LEDs) are fabricated by combining the yellow emission of YAG: Ce3+ with the blue light of the diode [7]
K(Ca, Sr)Y(PO4)2 activated with 5% of Eu3+ ions showed intense red emission, with a dominance of electric dipole transitions from the 5D0 to 7F2 level
The most intense emission was observed for the samples heat-treated at 500 ◦C
Summary
Inorganic phosphors doped with lanthanide ions have attracted much attention due to their potential applications as phosphors, laser materials, or solid-state lighting [1–6]. The current white-light-emitting diodes (W-LEDs) suffer from a lack of red light, red phosphors are sought to fill deficiency. W-LEDs are fabricated by combining the yellow emission of YAG: Ce3+ with the blue light of the diode [7]. The second method is to mix the blue, green, and red emissions generated from three or two blended powders. Rare-earth-doped (RE) phosphates are a good candidate for the formation of white LEDs due to their good physical and chemical stability, low cost of substrates, and reduced preparation temperatures compared to silicates, aluminosilicates, or nitrates [8–13]. One of the most promising phosphors are KMeRE(PO4) phosphates, where Me = Ca or Sr, and have a hexagonal structure with the unit cell parameters a = b ≈ 7.0 and c ≈ 6.4 Å [14–18].
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