ZnS is a wide band gap semiconductor material with Eg of 3.8eV and is used as a phosphor and also in thin-film electro-luminescence devices such as flat panel displays, light-emitting diodes, electroluminescence, solar cells, sensors, infrared windows, lasers and bio devices. ZnS Nano crystals are the highly dispersed Nano crystalline structures which mean the number of atoms located in the crystalline lattice is comparable to that of on the surface. Also ZnS is a nontoxic semiconductor and due to presence of polar surfaces, it finds prospects as excellent transport properties, good thermal stability and high electronic mobility. ZnS is considered as most suitable substance because of its distinguishing chemical, optical and electronic properties of crystalline phosphor. Physical and chemical properties, which are usually determined by the molecular structure of the bulk lattice, become increasingly dominated by the defective surface structure. A major drawback of application of pure ZnS is its large band gap which means it cannot only be activated in UV domain upon irradiation with photons of light, limiting its practical efficiency for solar and LEDs applications. Therefore, in order to enhance the solar efficiency of ZnS under solar irradiation, it was necessary to modify the nanomaterial to facilitate visible light absorption.
Novel luminescence characteristics for stable and visible-light emissions with different colors were observed upon doping of ZnS nanoparticles at room temperature. Doping of transition metals have shown promising results in achieving visible light active (VLA) photo catalysis. This has also resulted in formation of new energy levels between valance band (VB) and conduction band (CB) which also includes shifting of light absorption towards the visible light region.
In order to further research the doping effect, doping of alkali earth metals is being performed and the effects are being studied. This has shown some promising properties as decrease in band gap. Magnesium is a shiny, silver or gray colored metal that is light in weight and strong. The density of magnesium is 1.738 g/mL, which means the metal will sink in water, but it is still relatively light weight. Its phase is solid. Its crystalline structure is hexagonal and it can be beaten into extremely thin sheets.
It is capable of being shaped or bent. It is relatively soft and exhibits a shine or glow. The melting point of magnesium is 651°C (1,200°F) and boiling point is 1,100°C (2,000°F). The reason for doping Mg with ZnS is because Mg has a radius of 0.57? which is very close to the radius of Zn which is 0.60 ?.Hence ZnS can be easily doped with Mg.
Doping of Mg will widen the band gap of ZnS.Hence it can be easily tuned by varying the Mg concentration.