A critical role of pH in the combustion synthesis of nano-sized SrAl2O4:Eu2+, Dy3+ phosphor

Solution combustion synthesis of nano-crystalline SrAl2O 4:Eu2+, Dy3+ phosphor is investigated by varying the pH of the precursors solution, which plays an important role in phosphor's photoluminescence properties due to its ability to change the chemical environment of host structure surrounding Eu ions as an emission center. The best conditions for both intensity and decay behavior of the phosphor are achieved at pH of the precursors solution equal to 5.2, corresponding to the host structure composed of single-phase monoclinic SrAl2O4 without any impurity phases. Resulted phosphor shows a broad emission peak centered at 517 nm and excitation spectra consisting of two major peaks at 240 and 254 nm, well-known as characteristic peaks of this phosphor. Both the excitation and emission spectra of obtained nano-crystals shift to higher energies in contrast to the product of solid state method. These characteristic peaks are very weak or even absent in the samples resulted from precursors solution with higher or lower amount of pH than the "critical" pH. Crystallite size of the flake-shape particles is measured to be around 40 and 62 nm before and after thermal treatment, respectively.