Luminescence And Long-lasting Phosphorescence Properties Of Eu²⁺ Doped Oxynitride Phosphors

Eu²⁺-activated oxynitride phosphors are a series of down-conversion phosphors for white light-emitting diodes, which have drawn much attention to their wide applications in various fields. The oxynitride phosphors have excellent photoluminescence properties and outstanding thermal and chemical stability. They can match the UV and blue LED chip very well as the phosphors for white light-emitting diodes because of their strong absorption in the ultraviolet and visible light spectral region. The long-lasting phosphorescence phosphors for X-ray and cathode ray tubes can be applied in screen of radar. The main purpose of this work is to synthesize Eu²⁺-doped oxynitride phosphors and research their crystal structures, photoluminescence and long-lasting phosphorescence properties, the main results obtained are listed as follow:(1) Tuning Eu²⁺ concentration, it is observed that the photoluminescence excitation band edge of Ca_1-xEu_xSi₂O_2-δΝ_2+2δ/3 shifts to the longer wavelength side, following the formation of a strong excitation band at around 460 nm and this band becomes stronger with an increase in Eu²⁺ concentrations.(2) Synthesized the phosphors with the composition of Ba₂SiO₄:0.01Eu²⁺-xSi₃N₄ (x = 0.03, 0.1, 0.3, 0.5, 0.7, and 1.0). The XRD patterns of the samples are consistent with the Ba₂SiO₄ orthorhombic phase when the Si₃N₄ content is equal to or less than 0.1. After the removal of X-ray excitation source, the phosphor shows a weak LLP peak at 505 nm; When x = 0.1, the crystal structures of phosphors are consistent with the Ba₂SiO₄ orthorhombic phase. After the removal of X-ray excitation source, the phosphor shows bluish-green LLP peak at 490 nm; With increasing x from 0.1 to 1, BaSi₂O₂N₂ monoclinic phase is gradually formed and finally dominates the crystal phase as x = 1, the PL spectra are in accordance with the PL spectrum of BaSi₂O₂N₂:Eu²⁺ only, peaking at 490 nm.(3) Synthesized the phosphors with the composition of 2BaCO₃- ySi₃N₄: 0.01Eu²⁺ (y = 1/6, 1/4, 1/3, and 1.0) The XRD patterns of the samples are consistent with the Ba₂SiO₄ orthorhombic phase for y > 1/6; when y = 1/6, the content of Si₃N₄ may be too small to form a crystal phase but forms a eutectic mixture, the LLP spectrum shows a single broad orange-red band with a maximum at 590 nm, which should belong to the Ba₃SiO₅:Eu²⁺ phase. LLP of 2BaCO₃-ySi₃N₄: 0.01Eu²⁺ (y = 1.0) is detected to be enhanced by a factor of 7 in comparison with that of Ba₂SiO₄:0.01Eu²⁺–xSi₃N₄ (x = 0.03).(4) In order to improve the LLP intensity of the Ba₂SiO₄:Eu²⁺ phase, add some BaCO₃ into Ba₂SiO₄:0.01Eu²⁺-xSi₃N₄ and obtain the LLP phosphors with the composition of Ba₂SiO₄:0.01Eu²⁺-xSi₃N₄-2BaCO₃. The crystal structures of phosphors belong to Ba₂SiO₄ orthorhombic phase. When x =1.0, the LLP intensity is about three times as strong as that of 2BaCO₃- ySi₃N₄: 0.01Eu²⁺ (y = 1.0).