Enhanced Luminescence Properties of ZnS Nanoparticles for LEDs Applications via Doping and Phase Control

Cu- and Al-doped ZnS nanoparticles (NPs) were synthesized via a hot-injection method. The results indicate that the addition of Cu initially increases and subsequently decreases the luminescence intensity, reaching a peak at a Cu content of 0.5%. Furthermore, Al doping leads to a significant increase in luminescence intensity, accompanied by a blue-shift of the emission peaks. Additionally, an increase in the concentration of the Cu dopant induces a phase transition of ZnS from cubic to hexagonal at a low temperature. Moreover, a positive correlation is observed between the dopant concentration and the average particle size. The addition of Al results in a significant decrease in the average particle size, which ranges from approximately 3.59 to 4.34 nm. Although the band gap of ZnS is slightly reduced after doping, it remains stable. This study suggests that the addition of Al primarily forms a donor–acceptor pair with Cu, thereby enhancing Cu’s emission. Modulating the doping concentrations of Cu and Al can adjust the emission position while significantly increasing the photoluminescence quantum yield (PL QY) after doping. The highest PL QY is achieved with ZnS:0.5% Cu, 2.0% Al, which is 21.8 times higher than that of the undoped ZnS. This material has the potential to be employed in a variety of applications, including light-emitting diodes, inorganic scintillators, and anticounterfeiting techniques.