Characterization, luminescence and dye adsorption study of manganese and samarium doped and co-doped zinc sulfide phosphors

Luminescent materials are widely used for various applications such as light-emitting diodes (LEDs), thermoluminescence dating, phosphor thermometry, as well as phosphors. Zinc sulfide is one of the most common phosphors due to its facile preparation and relatively low materials cost. Herein, manganese-doped, samarium-doped, and co-doped zinc sulfides were successfully synthesized by a precipitation method. XRD results showed no other crystalline phases observed in the synthesized products. The synchrotron-XRF confirmed the successful incorporation of Mn and Sm into the doped and co-doped samples, in which approximately 10% of the initial doping amount of Mn and 1% of the initial concentration of Sm3+ were found. XAS analysis revealed the oxidation state and local structure of the manganese dopant and the zinc in the ZnS host matrix. SEM and TEM showed the agglomeration of nanoparticles into secondary particles with irregular shapes. A comparative study on the photoluminescence characteristics of the pristine ZnS and its corresponding doped phosphors thoroughly ensued. The result showed that all the samples had identical defect-derived fluorescence peaks. However, the addition of Mn2+ ion had led to the extra emission at the wavelength around the value of 607 nm corresponding to the T-4(1) to (6)A(1) transition within the Mn2+ activator. Interestingly, the samarium dopant shifted both the excitation and the emission maxima up to 11 nm and 10 nm, respectively. These shifts were not very high due to the limited incorporation of the samarium in the ZnS structure, as suggested by the synchrotron-XRF study. Our work, therefore, showed the prospects of tuning the bandgap energy of the transition doped ZnS by the addition of rare-earth ions. The N-2 sorption isotherms revealed the relatively high specific BET surface areas (similar to 171-196 m(2)/g). Apart from the luminescent applications, the present samples are also prospectively candidates for anionic-dye adsorption due to their dye selectivity.