Long afterglow calcium aluminate phosphors doped with Eu2+ and co-doped with Nd3+ /or Dy3+ (CaAl2O4:Eu2+, Nd3+, Dy3+) were fabricated by urea-nitrate solution – combustion method at 500 °C. The effects of varying concentrations of Ca:Al and co-dopants molar ratio (Nd3+:Dy3+) on the structural and luminescent properties of the phosphor were investigated. It was observed that Ca:Al molar ratios greatly affect the crystalline structure of the material. The results of the X-ray diffraction (XRD) analysis reveal that the formation of several crystalline phases depends on the molar ratios of the host material. The peaks show the presence of other phases such as Ca3Al2O6 and CaAl4O7 but the predominant phase formed was that of CaAl2O4. As the concentration of Ca ions increase, the peak intensity increase which led to formation of monoclinic CaAl2O4 as a single phase for the 1.5% Ca. However it was found that the crystalline structure is generally not affected by variation of the co-dopants concentration. PL studies revealed a general rise in intensity with increase in the mole ratio of Ca:Al . The highest PL intensity was observed with 1.5% Ca but was weak with 0.1% Ca. Also it is evident that as the fraction of Nd3+ increase and that of Dy3+ decrease proportionally good emission intensities are formed in the region 400nm-500nm at the ratio 1:1. The initial luminescent intensity and rate of decay vary from each other when co-doped with various proportions of Nd3+ and Dy3+. Low Nd3+ exhibited high initial luminescent intensity but low decay rate because of insufficient trap vacancies in the host matrix.
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