Effect of ZnS nanoparticles on the photoluminescence of Sm³⁺ions in methanol

Abstract

ZnS nanoparticles co-doped with Sm3+ ions were prepared in methanol medium for fixed Sm 3+ and varying ZnS concentrations. Enhancements in absorption as well as photoluminescence efficiency of the co-doped samples were observed. This enhanced efficiency is attributed to the effective increase in oscillator strengths of the Sm 3+ transitions because of the addition of ZnS nanoparticles.Keywords: Semiconductor nanoparticles, rare earth, photoluminescence, energy transfer. IntroductionThe photoluminescence (PL) properties of rare-earth (RE) elements have been a vast area of research for a few decades. An attractive feature of REs is their sharp and stable emission which depends strictly on the tri-positive RE ion and to some extent on the environment or host [1]. The Sm 3+ ion is one of the important RE ions which exhibits intense PL in the visible region. It finds wide applications in high-density optical storage, under sea communications, colour displays and visible solid-state lasers [2]. The application domains of Sm 3+ mainly depend on its emission characteristics. Hence there is a need of enhancing the emission efficiency of Sm 3+ in different hosts. One potential way of enhancement of the emission efficiency is by sensitization of the Sm 3+ ions with different entities viz. nanoparticles (NP), ligands, other REs etc. Semiconductor NPs possess very good potential in the area of sensitized luminescence because the band gap energy of the semiconductor NP is of the order of the emission energy of the RE ions. Also, since the absorption cross section of the semiconductor NPs is quite high in comparison to the RE ions, they can absorb excitation energy from the source and can sensitize the RE ions by the recombination of the electron hole pairs [3,4]. ZnS NPs have been extensively studied due to their outstanding optical properties. These are promising materials for absorption and emission in UV and visible (VIS) regions [5]. Nanosized ZnS exhibits discrete electron energy levels with high oscillator strength and strong luminescence due to the well known quantum confinement effects. Hence it bears potential as effective sensitizer for tri-positive RE ions [6]. The PL enhancement of Eu 3+ due to the energy transfer from ZnS to Eu 3+ in ZnS:Eu 3+ nanocrystal has been reported by Sun et al. [7]. Chen et al. have studied the energy transfer from ZnS to Tb 3+ with the help of absorption, excitation and PL of ZnS/ Tb 3+ in water, isooctane microemulsion and sodium bis