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The effect of isovalent and hypervalent ion doping on the structural and luminescence properties of sodium sulfate

Na2SO4, Na2SO4: Li, Na2SO4: Li, Eu, Na2SO4: Li, Dy and Na2SO4: Li, Eu, Dy phosphors were prepared using a slow evaporation technique followed by their subsequent calcination at 400 °C for 4 h. Doping with a Li+ ion stabilized the thenardite phase of the host matrix, while codoping with rare earth stabilized the phase transformation from stable thenardite to a metastable mirabilite crystal structure. The microstructure and morphology were studied using scanning electron microscopy and transmission electron microscopy. Thermoluminescence studies revealed that the isovalent doping of Li+ served as a quencher and the addition of the codopant introduced additional trap sites in the host matrix. The TL intensity followed the order Na2SO4: Li, Eu > Na2SO4: Li, Eu, Dy > Na2SO4: Li, Dy > Na2SO4 > Na2SO4: Li. The room temperature emission spectra of Li-doped, RE3+-codoped and undoped Na2SO4 were studied under ultraviolet radiation. For pure Na2SO4, the two peaks that appeared were at 364 nm and 702 nm. The emission intensities of RE3+-codoped samples increases with increase in dopant concentration.