# Phosphine-Free-Synthesized ZnSe/ZnS Core/Shell Quantum Dots for White Light-Emitting Diodes
## 2 Materials and Methods  
**Materials. ** To synthesize the ZnSe/ZnS C/S QDs, zinc oxide (ZnO, 99.99%), selenium (Se, 99.99%), sulfur (S, 99.9%), oleic acid (OA, 90%), 1-octadecene (ODE, 90%), hexane (95%), chloroform (95%), paraffin oil (analytical grade), acetone (analytical grade), and ethanol (EtOH, analytical grade) were purchased from Sigma-Aldrich. To synthesize the Zn-doped CuInS\({}_{2}\)/ZnS (ZCIS/ZnS) C/S QDs, copper (I) iodide (CuI, 99.999%), indium acetate (C\({}_{6}\)H\({}_{9}\)InO\({}_{6}\), 99.99%), zinc chloride (ZnCl\({}_{2}\), \(\geq\)98%), and 1-octanethiol (OTT, \(\geq\)98.5%) were purchased from Sigma-Aldrich. Sodium oleate (C\({}_{18}\)H\({}_{33}\)NaO\({}_{2}\), \(>\)97.0%) was purchased from Tokyo Chemical Industry. **Preparation of the Zn precursor. ** Two mmol of ZnO, OA (4.5 g), and paraffin oil (14 mL) were loaded in a three-neck flask and heated to 300 \({}^{\circ}\)C for 30 min under argon flow to obtain a colorless, clear solution. After the reaction was finished, the temperature was cooled to room temperature and the resulting Zn-oleate precursors were stored in an argon atmosphere. **Preparation of the Se precursor. ** Two mmol of Se and ODE (20 mL) were loaded in a three-neck flask and heated to 220 \({}^{\circ}\)C for 180 min under argon flow. After the reaction was complete, the temperature was cooled to room temperature and the Se precursors were stored in an argon atmosphere. **Preparation of the S precursor. ** For preparation, 2 mmol of S and ODE (20 mL) was loaded in a three-neck flask and heated to 150 \({}^{\circ}\)C for 30 min under argon flow. After the reaction was complete, the temperature was cooled to room temperature and the S precursors were stored in an argon atmosphere. **Synthesis of the ZnSe/ZnS C/S QDs. ** ZnSe/ZnS C/S QDs were synthesized via a hot-injection method with a slight modification of the previously reported method [23]. Two mL Se precursor and 4.5 mL paraffin oil were loaded in a 50 mL, three-neck flask and heated to 115 \({}^{\circ}\)C for 30 min under a vacuum. After the solution was degassed, the reaction temperature was increased to 310 \({}^{\circ}\)C under argon gas flow. Three mL of the Zn precursor solution was injected swiftly, and the temperature was kept at 310 \({}^{\circ}\)C for 1 h for ZnSe growth. To grow the ZnS shell on the ZnSe core, 1 mL of the S precursor was slowly injected dropwise into the core solution at 310 \({}^{\circ}\)C. At intervals of 10 min, 1 mL of the Zn precursor was injected dropwise into the core solution. After aging for 30 min under argon gas, the synthesized ZnSe/ZnS C/S QDs were washed with acetone, acetone/EtOH, and EtOH and finally dispersed in hexane for further study. Aliquots were taken at different time intervals to investigate growth kinetics by optical property characterization, such as UV-vis absorption and PL spectroscopy. **Synthesis of the Zn-doped CuInS\({}_{2}\)/ZnS (ZCIS/ZnS) C/S QDs. ** The ZCIS/ZnS C/S QDs were synthesized via a hot-injection method with a slight modification of the previous method [32]. Typically, a mixture of CuI (0.0238 g, 0.125 mmol), In(Ac)\({}_{3}\) (0.1459 g, 0.5 mmol), Zn-oleate (0.0126 g, 2 mmol), and 5 mL ODE was loaded in a three-neck flask and heated to 120 \({}^{\circ}\)C for 30 min under a vacuum. After the solution was degassed, the reaction temperature was increased to 230 \({}^{\circ}\)C under argon gas flow. Three mL of OTT was swiftly injected, and the temperature was kept at 230 \({}^{\circ}\)C for 10 min. A mixture of Zn stearate (2.5294 g, 4 mmol), 4 mL OA, and 2 mL ODE was injected dropwise into the reaction flask. After the injection of the Zn precursors, the reaction temperature was increased to 240 \({}^{\circ}\)C and kept for 270 min. The synthesized ZCIS/ZnS C/S QDs were washed with EtOH and dispersed in hexane for further use. **Fabrication of the ZnSe/ZnS QD-converted blue LEDs.