A composite material with a low refractive index that can be used for a light-emitting device, a light-receiving device, a light-emitting and light-receiving device, and the like is provided. The composite material includes a first organic compound and a second organic compound, the proportion of carbon atoms forming bonds by the sp.sup.3 hybrid orbitals in the total number of carbon atoms of the first organic compound is greater than or equal to 23% and less than or equal to 55%, and the second organic compound contains fluorine. Alternatively, an optical device including an anode, a cathode, and a first layer, in which the composite material is included in the first layer, is provided.

An organic light emitting device having a light emitting layer that contains first to fourth organic compounds satisfying the following formulae has a long emission lifetime and is stable. The second organic compound is a delayed fluorescent material, and the amount of light emission from the fourth organic compound is the maximum. E.sub.S1 is a lowest excited singlet energy, E.sub.T1 is a lowest excited triplet energy. E.sub.S1(1)>E.sub.S1(4)>E.sub.S1(2)>E.sub.S1(3), E.sub.T1(1)>E.sub.T1(2)>E.sub.T1(3)>E.sub.T1(4).

Provided is a light-emitting device and an electronic apparatus including the same. The light-emitting device includes: a first electrode; a second electrode facing the first electrode; an interlayer between the first electrode and the second electrode and including an emission layer; and a capping layer, wherein the emission layer includes a first emitter, the first emitter emits a first light having a first emission spectrum, the capping layer is in a path along which the first light travels, an emission peak wavelength of the first light is about 520 nm to about 550 nm, the first emitter includes platinum, the capping layer includes an amine-containing compound, and a value of a ratio of CIEy to reflective index (RCR value) of the first light extracted to the outside through the capping layer is 38 or less, and the RCR value is calculated according to Equation 1.

CIEy/R(cap)×100  Equation 1

A light-emitting device includes: a first electrode; a second electrode facing the first electrode; an interlayer arranged between the first electrode and the second electrode and including an emission layer; and a hole transport region arranged between the first electrode and the emission layer, wherein the hole transport region includes an electron blocking layer, and the electron blocking layer includes a heterocyclic compound represented by Formula 1.

A light-emitting device and an electronic apparatus including the same are provided. The light-emitting device includes a first electrode, a second electrode facing the first electrode, an interlayer between the first electrode and the second electrode and including an emission layer, and a capping layer. The emission layer includes a first emitter, the first emitter emits a first light having a first emission spectrum, the capping layer is in a path on which the first light travels, an emission peak wavelength of the first light is about 520 nm to about 550 nm. The first emitter includes iridium, the capping layer includes an amine-free compound, and the value of ratio of CIEy to reflective index (RCR value) of the first light extracted to the outside through the capping layer is 38 or less, and the RCR value is calculated according to CIEy/R(cap)×100.

A light-emitting device and an electronic apparatus including the same are provided. The light-emitting device includes a first electrode, a second electrode facing the first electrode, an interlayer between the first electrode and the second electrode and including an emission layer, and a capping layer. The emission layer includes a first emitter, the first emitter emits first light having a first emission spectrum, the capping layer is in the path on which the first light travels, an emission peak wavelength of the first light is from about 520 nm to about 550 nm. The first emitter includes iridium, the capping layer includes an amine-containing compound, and the value of ratio of CIEy to reflective index (RCR value) of the first light extracted to the outside through the capping layer is 38 or less, and the RCR value is calculated according to

CIEy/R(cap)×100.

Embodiments provide a polycyclic compound and a light emitting element that includes the polycyclic compound. The light emitting element includes a first electrode, a second electrode disposed on the first electrode, and at least one functional layer disposed between the first electrode and the second electrode, wherein the at least one functional layer includes the polycyclic compound, which is represented by Formula 1. Formula 1 is defined in the specification. The light emitting element exhibits a long service life.

##STR00001##

Provided are a light-emitting device and an electronic apparatus including the same. The light-emitting device includes a first electrode, a second electrode facing the first electrode, and an interlayer between the first electrode and the second electrode. The interlayer includes an emission layer, and a hole transport region between the first electrode and the emission layer. The emission layer includes a transition metal-containing organometallic compound. The hole transport region includes an electron-blocking layer. The electron-blocking layer includes a first electron-blocking material and a second electron-blocking material, and the first electron-blocking material and the second electron-blocking material have different hole mobilities.

Embodiments provide a cyclic compound, a light-emitting device including the cyclic compound, and an electronic apparatus including the light-emitting device. The light-emitting device includes a first electrode, a second electrode facing the first electrode, an interlayer between the first electrode and the second electrode and including an emission layer; and at least one cyclic compound. The cyclic compound is represented by Formula 1:

##STR00001##

The description of Formula 1 is provided in the specification.

A light-emitting device includes a first electrode, a second electrode facing the first electrode, and an interlayer between the first electrode and the second electrode. The interlayer includes an emission layer and a hole transport layer between the first electrode and the emission layer. The emission layer includes a first host, a second host, and a dopant, wherein the first host includes a hole-transporting host, and the second host includes an electron-transporting host or a bipolar host. The hole transport layer includes multiple hole transport layers, the hole transport layers each include a carbazole-based compound, and highest occupied molecular orbital (HOMO) energy levels of the carbazole-based compounds respectively included in neighboring ones of the hole transport layers are different from each other.