Light-emitting devices and displays with improved performance are disclosed. A light-emitting device includes an emissive material disposed between a first electrode, and a second electrode. Various embodiments include a device having a peak external quantum efficiency of at least about 2.2%; a device that emits light having a CIE color coordinate of x greater than 0.63; a device having an external quantum efficiency of at least about 2.2 percent when measured at a current density of 5 mA/cm2. Also disclosed is a light-emitting device comprising a plurality of semiconductor nanocrystals capable of emitting red light upon excitation, wherein the device has a peak luminescent efficiency of at least about 1.5 lumens per watt. Also disclosed is a light-emitting device comprising a plurality of semiconductor nanocrystals capable of emitting red light upon excitation, wherein the device has a luminescent efficiency of at least about 1.5 lumens per watt when measured at a current density of 5 milliamps/square centimeter. Also disclosed is a light-emitting device comprising a plurality of semiconductor nanocrystals capable of emitting green light upon excitation, wherein the device has a peak external quantum efficiency of at least about 1.1 percent. Further disclosed is a light-emitting device comprising a plurality of semiconductor nanocrystals, wherein the device has a luminescent efficiency of at least about 3 lumens per watt when measured at a current density of 5 mA/cm2. Further disclosed is a light-emitting device comprising a plurality of semiconductor nanocrystals capable of emitting green light upon excitation, wherein the device has an external quantum efficiency of at least about 2% when measured at a current density of 5 mA/cm2. Other light-emitting devices and displays with improved performance are disclosed. Also disclosed are methods for preparing and for purifying semiconductor nanocrystals.