Light-emitting device and electronic apparatus including the same

A light-emitting device comprising:

• a first electrode;
• a second electrode facing the first electrode;
• and
• an interlayer between the first electrode and the second electrode, wherein
• the interlayer comprises:
• an emission layer;
• a first compound that is a hole-transporting compound;
• a second compound that is an electron-transporting compound;
• a third compound comprising at least one nitrogen atom (N) as a ring-forming atom;
• and
• a fourth compound that is a nitrogen-containing compound,
• the fourth compound has a difference (ΔEST) between a lowest excited singlet state energy level and a lowest excited triplet energy level greater than or equal to about 0.4 eV, and
• the light-emitting device satisfies Condition 1 or Condition 2:
• KFRET>Krs [Condition 1]
• wherein in Condition 1,
• KFRET is a Forster resonance energy transfer (FRET) rate constant between the third compound and the fourth compound, and
• Krs is a luminescence rate constant of the third compound, and
• R0>RDA [Condition 2]
• wherein in Condition 2,
• R0 is a Forster radius between the third compound and the fourth compound, and
• RDA is a distance between a molecule of the third compound and a molecule of the fourth compound.