Synthesis of Cs 2 Ti 1-x Sn x I 6 . Mixed titanium-tin iodide VODPs were prepared using the same method used for the preparation of pure tin and pure titanium VODP NCs. 4 ml of cesium oleate and 60 mg of DMOP were loaded in a 50 ml three-neck flask together with Sn(IV) acetate and Ti(IV) isopropoxide in different ratio, 2 ml of ODE and 2 ml of OA. Since the difference in precursor ratios between pure Cs 2 TiI 6 and pure Cs 2 SnI 6 was quite large (Cs:Ti:I = 2:2.5:27 and Cs:Sn:I = 2:1:6 respectively), the percentage concentrations of tin and titanium precursors in the sample names refer to their pure synthesis ratios, such that the 50% sample was synthesized using a precursor ratio of Cs:Ti:Sn:I = 2:1.25:0.5:27. For all the mixed phases, an iodine ratio of 27 was used to avoid the formation of CsI. Table lists the precursor ratios used for all iodide alloy syntheses. The solution was degassed through 3 cycles of argon and vacuum and heated at 110 °C for 35 minutes under vacuum. At this point 1238 µL (8.436 mmol) of TMSI were injected and after 20 seconds the reaction was quenched by diluting the solution in 10 ml of toluene.