The development of undoped alkaline silicate and doped alkaline aluminate phosphors for white phosphorescence, dosimetry, and persistent luminescence applications

Abstract

The undoped SrSiO3/SiO2 phosphors prepared by both co-precipitation and hydrothermal methods at different Sr/Si molar ratios are reported. Undoped and Mn doped BaAl2O4 phosphor synthesized using combustion method are also reported. The X-ray diffraction measurements confirmed hexagonal phases of the SrSiO3,SiO2 and BaAl2O4:Mn in the prepared phosphors. The particle morphology of the prepared phosphors was observed to be somewhat agglomerated partcles in the alkaline silicate phosphors, whereas nano-sheets with uneven morphology with both nano-rods and hexagonal particles were observed in the BaAl2O4:Mn phosphor. EDS measurements confirmed the presence of Sr, Si, and O in the SrSiO3/SiO2 phosphors, together with their homogenous dispersion in the phosphors. The presence of Ba, Al, O, and Mn in the BaAl2O4:Mn phosphor was also confirmed by EDS measurement. PL measurements confirmed that the undoped phosphors possess room temperature phosphorescence properties with a 2:1 Sr/Si molar ratio sample prepared by co-precipitation method showing excellent white phosphorensce. A combination of two emission bands (495 and 687 nm) make up a white phosphorescence that cover a wide range of the spectrum, making this phosphor a potential candidate in solid state lighting applications. These emission bands were attributed to the intrinsic defects in the prepared SrSiO3/SiO2 phosphors. PL measurements also confirmed green room temperature phosphorescence from the BaAl2O4:Mn phosphor. Thermoluminescence studies showed more than one overlaping peaks in all samples except for the 2:1 Sr/Si molar ratio sample which showed only one peak at 100 oC. For this reason, further thermoluminescence studies on this phosphor were carried out to assess prospects of applications in dosimetry. In addition to the observation of a single peak in this phosphor, linearity in a wide range of dose in it also proved that this has a potential for application in dosimetry. Also, the emission band of this phosphor at 495 nm falls within the dosimetric requirement of emission range of 400 – 500 nm. Both the methods used to calculate the activation energy, the initial rise and variable heating rate yielded comparable results.