An approach to the synthesis of strontium aluminate based nanophosphors
Creators: name: Thompson, Nathan
Publisher: name: RMIT University
Year: 2024

description: This work describes a study of the synthesis and photoluminescent properties of strontium aluminate nano-phosphors co-doped with the lanthanide ions, Eu2+ and Dy3+, and the transition metal, Cr3+, prepared via a microemulsion synthesis followed by calcination. <br><br>Chapter one presents an overview of persistent luminescence phosphors, as well as the role lanthanides play in such phosphors, followed by an in-depth analysis of the mechanisms of persistent luminescence. The second half of the chapter presents a brief review of current synthetic methodologies for producing persistent luminescent phosphors, and concludes with a discussion of the advantages of the microemulsion synthetic technique especially control over particle size and the uniform distribution of the dopant concentration. <br><br>Chapter two describes the materials, apparatus and methodology utilized for the synthesis and analysis of the strontium aluminate nano-phosphors. The chapter focuses on the microemulsion methodology which was employed throughout this work, and the calcination procedures employed, in particular, the development of the two stage oxidative pre-calcination procedure. <br><br>Chapter three focuses on the synthesis of a blue emitting Sr4Al14O25nanophosphor doped with Eu2+ and Dy3+. This material was prepared utilizing, for the first time the microemulsion technique and two calcination routes were investigated, (i) a single stage calcination procedure, and (ii) a two stage calcination procedure, which employed oxidative pre-calcination at 1100°C for the first time. The single stage calcination required large concentrations of boric acid flux to produce optimal persistence afterglow characteristics, and also gave rise to impurities, such as glassy BO3 phases and carbon deposition, on the surface of the phosphor. For the two stage calcination procedure, oxidative pre-calcination was employed, removing the impurities identified, as well as lowering the concentration of boric acid required to achieve the optimal persistence afterglow. Significantly, oxidative pre-calcination enhanced the desirable characteristics of the phosphor, with deep trap states (I3) and the time constant of long lasting afterglow (τ3) increasing by approximately 60% and 50% respectively. Efficient charge transfer mechanisms brought about by the homogeneous distribution of dopant ions as a result of the microemulsion route was observed, with significant decreases in both dopant ion concentration, and concentration quenching compared to those previously reported. <br><br>The fourth chapter reports the synthesis of a green emitting SrAl2O4doped with Eu2+ and Dy3+prepared via the microemulsion technique and utilizing the oxidative pre-calcination route developed in Chapter 3. Persistence afterglow spectra revealed increased quantities of deep trap states comparable with those of the blue emitting phosphors, as well as efficient charge transfer, and reductions in concentration and concentration quenching as was found for the blue phosphors, with increases in I3 and τ3 of 50% and 60% respectively, when compared to a single stage calcination sample. <br><br>Chapter five describes, for the first time the synthesis of “red” emitting Sr4Al14O25 doped with Eu2+, Dy3+ and Cr3+, prepared via the microemulsion technique and oxidative pre-calcination route. These red emitting phosphors exhibited efficient charge transfer and concentration reductions similar to those observed for the blue and green phosphors, leading to an approximately 30-40% increase in afterglow persistence. <br><br>