Solid state synthesis of SrAl2O4:Mn2+ co-doped with Nd3+ phosphor and its optical properties

The optical properties of alkaline earth aluminates doped with rare earth ions have received much attention in the last years and this is due to their chemical stability, long-afterglow (LAG) phosphorescence and high quantum efficiency. However, there is a lack of understanding about the nature of the rare earth ion trapping sites and the mechanisms which could activate and improve the emission centers in these materials. Therefore a new phosphor material composition, SrAl2O4:Mn 2+ , co-doped with Nd 3+ was synthesized by a traditional solid-state reaction method. The influence of transition metal and rare earth doping on crystal structure and its luminescence properties have been investigated by using X-ray diffraction (XRD), Raman scattering, Photoluminescence (PL) and Radioluminescence (RL). Analysis of the related diffraction patterns has revealed a major phase characteristic of the monoclinic SrAl2O4 compound. Small amounts of the dopants MnCO3 and Nd2O3 have almost no effect on the crsytalline phase composition. Characteristic absorption bands from Nd 3+ 4f–4f transitions in the spectra can be assigned to the transitions from the ground state 4 I9/2 to the excited states. The luminescence of Mn 2+ activated SrAl2O4 exhibits a broad green emission band from the synthesized phosphor particles under different excitation sources. This corresponds to the spin-forbidden transition of the d-orbital electron associated with the Mn 2+ ion. In photo- and radio-luminescence spectra, Nd 3+ 4f–4f transition peaks were observed. The emitted radiations for different luminescence techniques were dominated by 560, 870,1057 and 1335 nm peaks in the visible and NIR regions as a result of 4 I9/2- 4 G7/2 and 4 F3/2- 4 IJ (J¼9/ 2, 11/2 and 13/2) transitions of Nd 3+ ions, respectively. Multiple emission lines observed at each of these techniques are due to the crystal field splitting of the ground state of the emitting ions. The nature of the emission lines is discussed.