Synthesis and photoluminescent properties of wurtzite ZnS nanorods by hydrothermal and co-precipitation methods

Abstract

Nanorods of wurtzite ZnS were synthesized by a hydrothermal method at 200 degrees C and a co-precipitation method at room temperature in the presence of ethylenediamine (en) aqueous solutions. It was found that the wurtzite ZnS nanorods with uniform diameter around 80 +/- 20 nm, length about 300 +/- 100 nanometer appears at a proper concentration of en, unit [Zn] : [S] ratio, and an appropriate duration by the hydrothermal method. Much longer wurtzite ZnS nanorods with length from 300 to 2000 nm and diameter from 80 to 200 nm were obtained via the co-precipitation method. A very minor undecomposed ZnS center dot 0.5en phase coexisted with the wurtzite ZnS nanorods in the co-precipitation method was identified and arguably thought to be due to the low temperature used. ZnO coated ZnS core-shell structures were successfully fabricated by annealing the ZnS nanorods in an oxygen flow at 650 degrees C for 3-5 min. The coating of ZnO layer on ZnS nanorods results in a significant increase of photoluminescence (PL) intensity (30 times) at 490-500 nm visible regions for those of hydrothermal method and mild increase (double) for those of co-precipitation method.