Inorganic phosphors have luminescent properties and are used for commercial flat panel displays (FPDs). Mn2+ doped Zn2SiO4 and zinc sulfide phosphors are considered suitable materials for a FPD. Spherical Zn2SiO4 particles can be made using ZnSO4 as zinc source in an ammonia solution under a hydrothermal condition.
Luminescence efficiency of zinc sulfide is satisfactory, but its stability under a cathode ray beam in high vacuum is questionable. This problem is overcome by a surface passivating agent layer (PAL), which is a new class of luminescence materials of doped nanocrystals combining high luminescence efficiency and decay time shortening. The doping of Mn2+ into ZnS lattice is achieved during the precipitation at room temperature in the solution or during the reaction of cations with H2S gas at an elevated temperature up to 200°C. Methacrylic acid (MA) is used as a surfactant in order to prevent nanoparticle agglomeration in the solution. PL enhancement up to ten-fold has been observed for polymethyl merthacrylate (PMMA) coated ZnS nanocrystals doped with Mn2+ ions.

Mn2+ doped ZnS nanocrystals are synthesized by a chemical precipitation method at room temperature using Zn(CH3COO)2 • 2H2O, Mn(CH3COO)2 • 4H2O and Na2S • 9H2O as starting materials.
A 50 mL ethanol solution is prepared by dissolving 2.195 g Zn(CH3COO)2 • 2H2O and 0.049 g Mn(CH3COO)2 • 4H2O with stirring at room temperature. This yields a Mn2+ doping concentration of 2 mole%. Then, a 50 mL aqueous solution of 2.451 g Na2S • 9H2O is added to the ethanol solution drop by drop with vigorous stirring. This results in white precipitate, which is centrifuged and washed using deionized water. Finally, 1.987 g of 3-methacryloxypropyl trimethoxysilane (MPTS) is added to the resultant mixture after centrifuging and washing.
Both photoluminescence and cathodoluminescence are observed from these Mn2+ doped Zn2SiO4 phosphor particles. A 30-fold enhancement has been observed after the surface passivation. This is achieved by eliminating the surface defects, in which the carboxylic groups with effective resonance/inductive effect in the surface modifying agent plays an important role.

The above work on green light emitting nanoparticle is from a report of researchers at Clemson University.