BACKGROUND

1. Technical Field

The present disclosure relates to a quantum dot and a preparation method thereof, and more particularly, to a core-shell type light-emitting quantum dot and a preparation method thereof.

2. Description of the Related Art

Quantum dots are nano-sized particles. Owing to their size which is smaller than twice the Bohr exciton radius of an electron, quantum confinement occurs, forming a discontinuous energy band. Accordingly, the quantum dot has characteristic of spontaneous fluorescence after being stimulated. Such light and electrical characteristics caused by the special effect allows the quantum dot materials to be widely applied in the fields of light emitting diodes, solar cells, photodetectors, liquid crystal displays, color enhancement films, color filters, and so on.

The existing quantum dot materials, however, have problems such as insufficient color purity and luminous efficiency due to the difficulty in controlling their dimensional uniformity. Furthermore, the existing quantum dots have insufficient resistance to temperature and insufficient water and oxygen barrier properties, which not only affect the stability of the applied device, but also limit the promotion and application of such materials.

Therefore, there lies a need for a light-emitting quantum dot with high luminous efficiency, high color purity, good barrier property for water as well as oxygen, and good temperature resistance.

SUMMARY

The present disclosure provides a core-shell type light-emitting quantum dot comprising: an alloy core which consists of Cd, Se, Zn, and S, wherein an element ratio of Zn and S each accounts for 30% to 50% of the overall core, and a content of Cd and Se gradually decreases outward from the core center; and a shell layer which has a zinc blende structure and is coated on a surface of the alloy core.

In an embodiment of the present disclosure, a D90 particle size of the light-emitting quantum dot is 12 to 15 nanometers, and the alloy core has a radius of 3 nanometers or less.

In an embodiment of the present disclosure, the light-emitting quantum dot has an appearance of polygon with a plurality of corners.

In an embodiment of the present disclosure, the shell layer consists of ZnS.

In an embodiment of the present disclosure, an element ratio of Cd and Se each accounts for 3% to 10% of the overall core.

The present disclosure further provides a method for preparing the core-shell type light-emitting quantum dot, comprising: providing a metal precursor solution containing a Cd metal precursor and a Zn metal precursor and activated by a reactive amine; mixing and reacting a first ion stock solution containing S ions and Se ions with the activated metal precursor solution containing the Cd metal precursor and the Zn metal precursor to obtain a solution containing an alloy core; and adding a second ion stock solution containing S ions and a zinc salt to the solution containing the alloy core for an reaction of forming a shell layer which is coated on a surface of the alloy core, thereby obtaining the core-shell type light-emitting quantum dot.

In an embodiment of the method of the present disclosure, the Cd metal precursor is at least one selected from CdO and Cd(ac)2. The Zn metal precursor is at least one selected from ZnO and Zn(ac)2.

In an embodiment of the method of the present disclosure, the activated metal precursor solution containing the Cd metal precursor and the Zn metal precursor is prepared by a process comprising: providing a metal precursor solution containing the Cd metal precursor; activating the Cd metal precursor in the metal precursor solution containing the Cd metal precursor and the Zn metal precursor by a reactive amine and a reactive acid; and adding the Zn metal precursor to the activated metal precursor solution containing the Cd metal precursor to activate the Zn metal precursor at a temperature of from 300° C. to 320° C.

In an embodiment of the method of the present disclosure, the activated metal precursor solution containing the Cd metal precursor and the Zn metal precursor is prepared by a process comprising: providing a metal precursor solution containing the Cd metal precursor and the Zn metal precursor; activating the Cd metal precursor in the metal precursor solution containing the Cd metal precursor and the Zn metal precursor by a reactive amine and a reactive acid; and heating the activated metal precursor solution containing the Cd metal precursor and the Zn metal precursor to a temperature of from 300° C. to 320° C. to activate the Zn metal precursor therein.

In an embodiment of the method of the present disclosure, the reactive acid is oleic acid. In another embodiment, the reactive amine and the reactive acid has a molar ratio of from 1:7 to 1:7.5.

In an embodiment of the method of the present disclosure, the activation temperature of the Cd metal precursor is 300° C. to 320° C.

In an embodiment of the method of the present disclosure, the reactive amine is a primary amine. In another embodiment, the primary amine is oleylamine.

In an embodiment of the method of the present disclosure, the reaction temperature for preparing the alloy core is from 280° C. to 310° C., and the reaction time is 10 to 20 minutes.

In an embodiment of the method of the present disclosure, the step of adding the second ion stock solution containing the S ions and the zinc salt further comprises a step of firstly adding the second ion stock solution containing the S ions to the solution containing the alloy core for a reaction; and after the reaction for 15 to 20 minutes, adding the zinc salt to react for 20 to 30 minutes.

In an embodiment of the method of the present disclosure, the zinc salt is zinc oleate.

In an embodiment of the method of the present disclosure, a reaction temperature for forming the shell layer is 240° C. to 270° C.

In an embodiment of the method of the present disclosure, the reactive amine, the Cd metal precursor and the Zn metal precursor have a molar ratio of from 3:0.14:5.9 to 3:1:5.9.

In an embodiment of the method of the present disclosure, the Cd metal precursor, the Zn metal precursor, the S ions and the Se ions have a molar ratio of from 0.14:5.9:4.2:1.5 to 1:5.9:4.2:1.5.

Based on the preparation method of the present disclosure, a core-shell type light-emitting quantum dot with an alloy core having excellent dimensional uniformity may be obtained, and the luminous color purity may be improved. Moreover, because a reactive amine is used for activation in the present disclosure, a shell layer with a zinc blende structure may be formed on the alloy core. The shell layer with the zinc blende structure provides effective protection for the alloy core, such that the quantum efficiency of the prepared core-shell type light-emitting quantum dot may reach 95%, and the quantum dot may have high temperature resistance and excellent water- and oxygen-barrier performance.

