Numerous phosphors have been extensively investigated for use in white light emitting diodes (LEDs) using blue or near-ultraviolet (nUV) chips. Among them, Alkaline earth metal aluminates and (oxy)nitride systems, which have high chemical and thermal stabilities, high quantum efficiencies, and broad excitation spectra, are commercially used as green and red phosphors.
In this work, red, green and blue phosphors were investigated for the application to white LEDs. Red emitting Mn4+-doped CaAl4O7 (CA2) and CaAl12O19 (CA6) powders were prepared under different conditions, with changes in the amounts of flux, Mn concentration, and mole ratio of Al2O3 to CaCO3 in the starting mixtures, which affected the structure and the luminescence. CA2 : Mn4+ and CA6:Mn4+ had the same excitation and emission spectra but with different intensities. The excitation spectra exhibited broad bands (320 - 470 nm) centered at 395 nm, while red emission bands were observed at 656 nm. The emission intensity of CA6 : Mn4+ was nearly twice as high as that of CA2 : Mn4+, as the Mn4+ ions were located in an octahedral crystal field in the CA6, but not in the CA2.
Green, red emitting Sr2?y?zCazSi(O1?xNx)4:yEu2+ (SCSON:Eu2+) solid solutions were prepared by substituting N3?, Eu2+, and Ca2+ ions into Sr2SiO4 (SSO). These ions contributed differently to the evolution of luminescence of SCSON:Eu2+. SSON:Eu2+ (z= 0) has two activation centers: Eu(I) and Eu(II). The nitridation effects led to a dramatic change in the crystal field surrounding the Eu(II) site but rarely affected the Eu(I) site. Accordingly, SSON:Eu2+ exhibited broad excitation spectra from ultraviolet to visible wavelengths. In comparison with the Eu(II) green emissions of SSO:Eu2+, the dominant peak wavelengths (DPWs) of the Eu(II) emissions were at red emission regions (605 ? 630 nm), depending on the amount of Eu2+ ions. The Ca2+ ions of SCSON:Eu2+ preferentially changed the emission wavelength assigned to Eu(I) and affected the Eu(II) emission intensity. In addition to the spectral properties, the chromaticity coordinates and a low thermal quenching behavior of SCSON:Eu2+ powders demonstrated that they can be a novel red phosphors for use in white light emitting diodes.
Cyan-emitting (Ba,Ca)Si7N10:Eu2+was synthesized using a high-temperature graphite furnace. The excitation spectra peaked at 368 nm and decay times were apparently different from those of earlier papers, and these differences were explained by the structural analyses. The substitution of Ca2+ ions for Ba2+ ions increased the emission intensity by approximately 130%, as this resulted in local lattice modification. The findings indicate that (Ba,Ca)Si7N10:Eu2+ phosphors are highly stable and well suited for use in white LEDs pumped by near -ultraviolet sources.