An organic electroluminescent device and a display apparatus. The organic electroluminescent device includes a first electrode, a second electrode and an organic layer located between the first electrode and the second electrode. The organic layer includes a light-emitting layer. The light-emitting layer contains a host material, a thermally activated delayed fluorescence sensitizer and a fluorescent dye. The energy level relationship between the host material and the thermally activated delayed fluorescence sensitizer is LUMO.sub.host≥LUMO.sub.sensitizer, while HOMO.sub.sensitizer≥HOMO.sub.host.

An organic electroluminescent device and a display apparatus. The organic electroluminescent device includes a first electrode, a second electrode and at least two organic electroluminescent units located between the first electrode and the second electrode. The at least two organic electroluminescent units are arranged in a stacked manner. The at least two organic electroluminescent units include a first organic electroluminescent unit. The first organic electroluminescent unit includes a first light-emitting layer. The first light-emitting layer contains a first host material, a thermally activated delayed fluorescence sensitizer and a first fluorescent dye.

A novel light-emitting device that is highly convenient, useful, or reliable is provided. The light-emitting device includes a first electrode, a second electrode, a unit, and a first layer. The second electrode includes a region overlapping with the first electrode. The unit includes a region positioned between the first electrode and the second electrode. The unit includes a second layer and a third layer. The second layer includes a region where the third layer is positioned between the second layer and the first electrode. The second layer contains a light-emitting material. The first layer includes a region positioned between the third layer and the first electrode. The first layer contains a material having an acceptor property and a first material. The first layer includes a first region and a second region. The first region includes a region positioned between the second region and the first electrode. The first region contains the material having an acceptor property at a first concentration. The second region contains the material having an acceptor property at a second concentration. Note that the second concentration is higher than zero and lower than the first concentration.

The present disclosure relates to an organic light emitting diode that includes a first electrode; a second electrode facing the first electrode; and a first emitting material layer including a first compound and a second compound and positioned between the first and second electrodes, wherein an overlap ratio between an absorption spectrum of the first compound and an emission spectrum of the second compound is equal to or greater than 35%, and an organic light emitting display including the organic light emitting diode.

An organometallic compound, represented by Formula 1:

##STR00001## wherein M.sub.1 is a transition metal; X.sub.10 is C; X.sub.11 to X.sub.14, X.sub.20, X.sub.30 to X.sub.36, and X.sub.40 are each independently C or N; ring A.sub.20 and ring A.sub.40 are each independently a C.sub.5-C.sub.30 carbocyclic group or a C.sub.1-C.sub.30 heterocyclic group; and R.sub.1 to R.sub.5, R.sub.10, R.sub.20, R.sub.31, R.sub.32, R.sub.40, R.sub.51, R.sub.52, T.sub.1, b10, b20, b31, b32, and b40 are as defined herein.

Provided are a heterocyclic compound represented by Formula 1-1 or 1-2, an organic light-emitting device including the heterocyclic compound, and an electronic apparatus including the organic light-emitting device:

##STR00001##

Formulae 1-1 and 1-2 may each be understood by referring to the descriptions of Formulae 1-1 and 1-2 provided herein.

Provided are a polycyclic compound represented by Formula 1 and an organic light-emitting device and an electronic apparatus, each including the same.

The present invention relates to a an organic electroluminescent device comprising at least one light-emitting layer B comprising at least one host material H.sup.B, at least one thermally activated delayed fluorescence (TADF) material E.sup.B, and at least one small full width at half maximum (FWHM) emitter S.sup.B wherein E.sup.B transfers energy to S.sup.B and S.sup.B emits light with an emission maximum in the wavelength range from 500 nm to 560 nm.

The present invention provides nanostructure compositions and methods of producing nanostructure compositions. The nanostructure compositions comprise a population of nanostructures comprising donor-acceptor ligands. The present invention also provides nanostructure films comprising the nanostructure compositions and methods of making nanostructure films using the nanostructure compositions.

A compound comprising a first ligand L.sub.A of Formula I or Formula II: ##STR00001## wherein A.sup.1 and A.sup.2 are each independently C or Si; wherein each R.sup.A, and R.sup.B independently represents mono to the maximum allowable substitution, or no substitution; wherein each X.sup.1, X.sup.2, and X.sup.3 is independently C or N; wherein each R, R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.A is independently a hydrogen or a substituent selected from the group consisting of deuterium, halogen, alkyl, cycloalkyl, heteroalkyl, heterocycloalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, boryl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carboxylic acid, ether, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinations thereof; wherein L.sub.A is complexed to a metal M; wherein M is optionally coordinated to one or more other ligands; wherein the ligand L.sub.A is optionally linked with the one or more other ligands to form a tridentate, tetradentate, pentadentate, or hexadentate ligand; and wherein any two substituents are optionally joined or fused together to form a ring.