BACKGROUND

Technical Field

The present disclosure relates to semiconductor nanoparticles, a method of producing the semiconductor nanoparticles, and a light-emitting device using the semiconductor nanoparticles.

Description of Related Art

White light-emitting devices, which are used as backlights of liquid crystal display devices and the like and which utilize photoluminescence emission from quantum dots (also called “semiconductor quantum dots”), have been proposed. Fine particles of a semiconductor with a particle size of 10 nm or less, for example, are known to exhibit a quantum size effect. Such nanoparticles are called the quantum dots. The quantum size effect is a phenomenon where a valence band and a conduction band, each of which is regarded as continuous in bulk particles, become discrete when the particle size is on the nanoscale, whereby a bandgap energy is varied in accordance with their particle size.

Quantum dots absorb light and emit light corresponding to the bandgap energy thereof. Thus, quantum dots can be employed as a wavelength conversion material in light-emitting devices. Light-emitting devices using quantum dots are proposed, for example, in Japanese Unexamined Patent Application Publication No. 2012-212862 and Japanese Unexamined Patent Application Publication No. 2010-177656. More specifically, a portion of the light emitted from a light-emitting diode (LED) chip is absorbed by quantum dots, and photoluminescence of another color is emitted from the quantum dots. The photoluminescence emitted from the quantum dots and the light from the LED chip not absorbed by the quantum dots are mixed to produce white light.

In these patent application documents, use of quantum dots made of a Group 12-Group 16 material, such as CdSe or CdTe, or a Group 14-Group 16 material, such as PbS or PbSe, is proposed.

One of the advantages of using quantum dots in light-emitting devices is that light with a wavelength corresponding to a bandgap of the quantum dots can have a peak with a relatively narrow full width at half maximum. Of the quantum dots proposed as the wavelength conversion material, quantum dots made of a binary semiconductor, typified by Group 12-14 semiconductors, such as CdSe, are confirmed to emit the light with the wavelength corresponding to the bandgap of the quantum dots, i.e., band-edge emission. Meanwhile, ternary quantum dots, in particular, Group 11-13-16 quantum dots have not been confirmed to exhibit the band-edge emission.

The light emission from the Group 11-13-16 quantum dots is caused by the defect levels at the surface or inside of the particles, or by the donor-acceptor-pair recombination, so that such light has a broad photoluminescence peak with a wide full width at half maximum and a long photoluminescence lifetime. Such light emission is not suitable for light-emitting devices, particularly, used in a liquid crystal display device. This is because a light-emitting device used in a liquid crystal display device is required to emit light with a narrow full width at half maximum that has a peak wavelength corresponding to each of three primary colors (i.e., RGB) in order to ensure high color reproducibility. For this reason, practical applications of the ternary quantum dots have not been prompted despite their less toxic compositions.

SUMMARY

Therefore, one object of certain embodiments of the present disclosure is to provide semiconductor nanoparticles that are configured to produce band-edge emission from ternary quantum dots of which composition can be less toxic, and a method of producing the semiconductor nanoparticles.

According to certain embodiments of the disclosure, a method of producing semiconductor nanoparticles, the method includes:

(a) providing a salt of Ag, a salt of In, a source compound of S, and an organic solvent; and

(b) placing the salt of Ag, the salt of In, and the source compound of S into the organic solvent so that the ratio of the number of atoms of Ag to the total number of atoms of Ag and In is 0.33 or more and 0.42 or less to obtain semiconductor nanoparticles.

According to other certain embodiments of the disclosure, a method of producing core-shell semiconductor nanoparticles includes:

providing a dispersion in which semiconductor nanoparticles that are produced by the method of producing semiconductor nanoparticles according to the above embodiments are dispersed into a solvent,

adding, to the dispersion, a compound containing a Group 13 element and an elemental substance of a Group 16 element or a compound containing a Group 16 element, to form a semiconductor layer consisting essentially of the Group 13 element and the Group 16 element on a surface of each of the semiconductor nanoparticles.

According to further other certain embodiments of the disclosure, semiconductor nanoparticles contain Ag, In, and S, and have an average particle size of 50 nm or less.

The ratio of the number of atoms of Ag to the total number of atoms of Ag and In is 0.320 or more and 0.385 or less.

The ratio of the number of atoms of S to the total number of atoms of Ag and In is 1.20 or more and 1.45 or less.

The semiconductor nanoparticles are adapted to emit photoluminescence having a photoluminescence lifetime of 200 ns or less upon being irradiated with light having a wavelength in a range of 350 to 500 nm.

According to further other certain embodiments of the disclosure, a core-shell semiconductor nanoparticle includes a core and a shell covering a surface of the core and being in heterojunction with the core.

The core is made of a semiconductor that contains Ag, In, and S, wherein the ratio of the number of atoms of Ag to the total number of atoms of Ag and In is 0.320 or more to 0.385 or less, and the ratio of the number of atoms of S to the total number of atoms of Ag and In is 1.20 or more and 1.45 or less.

The shell is a semiconductor that consists essentially of a Group 13 element and a Group 16 element.

In a photoluminescence spectrum obtained when the core-shell semiconductor nanoparticle is irradiated with light having a wavelength in a range of 350 to 500 nm, a photoluminescence peak having a peak wavelength in a range of 550 nm to 650 nm and a full width at half maximum of 80 nm or less is observed.

According to further other certain embodiments of the disclosure, a light-emitting device including a light conversion member and a semiconductor light-emitting element, wherein the light conversion member contains the above semiconductor nanoparticles according to certain embodiments of the disclosure.

The semiconductor nanoparticles according to certain embodiments of the disclosure is made of a semiconductor that contains Ag, In, and S, which correspond to a Group 11 element, a Group 13 element, and a Group 16 element, respectively, wherein the ratio of the number of atoms of Ag to the total number of atoms of Ag and In and the ratio of the number of atoms of S to the total number of atoms of Ag and In are respectively in a specific range, and photoluminescence emission with a short photoluminescence lifetime, i.e., the band-edge emission, is obtained. The semiconductor nanoparticles can have composition that contains neither Cd nor Pb, which are highly toxic. Thus, the semiconductor nanoparticles can be applied to products that are prohibited from using Cd or the like. Therefore, such semiconductor nanoparticles are suitable for use as a wavelength conversion material for light-emitting devices used in the liquid crystal display device or the like or as a biomolecule marker. Furthermore, with the method of producing semiconductor nanoparticles as described above, the ternary semiconductor nanoparticles that exhibit band-edge emission can be relatively easily produced.

