CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2019-0035403, filed on Mar. 27, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

1. Field

The present invention relates to an upconversion nanophosphor and a method of synthesizing the same and, more particularly, to an upconversion fluoride nanophosphor and a method of synthesizing the same.

2. Description of the Related Art

An upconversion nanophosphor refers to a phosphor including luminescent nanoparticles having a small diameter equal to or less than 100 nm and capable of absorbing low-energy light and emitting high-energy light. A phosphor generally has a structure in which an inorganic base material is doped with a lanthanide element, and an upconversion nanophosphor generally absorbs infrared light and emits visible light [Chem. Rev. vol. 104, 139-174 (2004)]. An upconversion nanophosphor generally includes a ceramic base material doped with trivalent lanthanide ions, emits light due to 4f-4f electronic transition of the trivalent lanthanide ions, and thus exhibits luminescence of a unique color based on the type of the lanthanide element regardless of the type of the host material or the diameter of nanoparticles [Luminescent Materials (1994)].

Most upconversion nanophosphors emit green or blue light by absorbing 980-nm infrared light. However, the infrared light used as excitation light in this case penetrate deeply into a body part, whereas the green or blue light emitted from the nanophosphors does not. As such, research has been currently conducted on an upconversion nanophosphor for emitting red light by absorbing 980-nm infrared light. However, in this case, energy from erbium (Er) used as an activator is transferred to manganese (Mn) [Angew. Chem. Int. Ed. 50, 10369, (2011)], or energy from holmium (Ho) used as an activator is transferred to cerium (Ce) used as a co-sensitizer, and thus a luminescence intensity is reduced [Nanotechnology 20, 385704 (2009)]. Meanwhile, 980-nm infrared light used as excitation light is easily absorbed by water molecules and thus a part onto which the 980-nm infrared light is irradiated may be increased in temperature to kill cells or damage tissues. As such, a nanophosphor capable of exhibiting luminescence by using 800-nm infrared light has been currently reported. The currently reported upconversion nanophosphor emits red light by absorbing 980 nm infrared light and 800-nm infrared light based on energy transfer from an activator to a co-sensitizer, and thus emission of intense red light may not be easily achieved [ACS Appl. Mater. Interfaces 10, 12331 (2018)]. Therefore, when developed, an upconversion nanophosphor capable of emitting intense red light by absorbing infrared light of a wavelength other than 980 nm will be appropriately usable as a fluorescent contrast agent and will also be usable as an anti-counterfeiting security material by using properties of emitting red light under irradiation of light of various wavelengths.

SUMMARY OF THE INVENTION

The present invention provides an upconversion nanophosphor capable of emitting intense red light by absorbing infrared light of a wavelength other than 980 nm, and a method of synthesizing the same. However, the scope of the present invention is not limited thereto.

According to an aspect of the present invention, there is provided a fluoride nanophosphor using, as cores, nanoparticles expressed by Chemical Formula 1.
LiEr1-x-yLyF4:Tm3+x[Chemical Formula 1]

(In Chemical Formula 1, x is a real number satisfying 0≤x≤0.3, y is a real number satisfying 0≤y≤0.8 and is selected within a range satisfying 0≤x+y≤0.9, and L is any one selected from the group consisting of yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), ytterbium (Yb), lutetium (Lu), and a combination thereof.)

The fluoride nanophosphor may further include first shells surrounding at least parts of the cores, and the first shells may be made of a material expressed by Chemical Formula 2.
LiGd1-p-qMqF4:Yb3+p[Chemical Formula 2]

(In Chemical Formula 2, p is a real number satisfying 0≤p≤1, q is a real number satisfying 0≤q≤1, p and q are selected within a range satisfying 0≤p+q≤1, and M is any one selected from the group consisting of rare-earth elements such as Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, erbium (Er), thulium (Tm), and Lu, and a combination thereof.)

The fluoride nanophosphor may further include second shells surrounding at least parts of the cores and the first shells, and the second shells may be made of a material expressed by Chemical Formula 3.
LiY1-r-s-tNtF4:Nd3+r,Yb3+s[Chemical Formula 3]

(In Chemical Formula 3, r is a real number satisfying 0<r≤1, s is a real number satisfying 0≤s≤0.5, t is a real number satisfying 0≤t≤1, r, s, and t are selected within a range satisfying 0<r+s+t≤1, and N is any one selected from the group consisting of rare-earth elements such as La, Ce, Pr, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Tm, and Lu, and a combination thereof.)

The fluoride nanophosphor may further include third shells surrounding at least parts of the cores, the first shells, and the second shells, and the third shells may be made of a material expressed by Chemical Formula 4.
LiGd1-uQuF4[Chemical Formula 4]

(In Chemical Formula 4, u is a real number satisfying 0≤u≤1, and Q is any one selected from the group consisting of rare-earth elements such as Y, La, Ce, Pr, Sm, Eu, Tb, Dy, Ho, Yb, Er, and Lu, and a combination thereof.)

The nanophosphor consisting of the cores may have a diameter of 1 nm to 40 nm.

The nanophosphor consisting of the cores and the first shells may have a diameter of 2 nm to 60 nm.

The nanophosphor consisting of the cores, the first shells, and the second shells may have a diameter of 3 nm to 80 nm.

The nanophosphor consisting of the cores, the first shells, the second shells, and the third shells may have a diameter of 4 nm to 100 nm.

The fluoride nanophosphor may emit red light by an excitation light source having a wavelength other than 980 nm.

According to another aspect of the present invention, there is provided a method of synthesizing a fluoride nanophosphor, the method including a complex formation step for forming a complex by using a first precursor, an erbium (Er) precursor, a thulium (Tm) precursor, and a sodium (Na) precursor, a first mixture solution formation step for forming a first mixture solution including the complex, oleic acid, and 1-octadecene, a reaction solution formation step for forming a reaction solution by mixing the first mixture solution with a second mixture solution including a lithium (Li) precursor, a fluorine (F) precursor, and alcohol, and a nanoparticle formation step for forming nanoparticles by removing alcohol from the reaction solution and performing heat treatment on the alcohol-removed reaction solution, wherein the nanoparticles include fluoride nanoparticles doped with Er3+and expressed by Chemical Formula 1, and wherein the first precursor includes any one selected from the group consisting of a yttrium (Y) precursor, a lanthanum (La) precursor, a cerium (Ce) precursor, a praseodymium (Pr) precursor, a neodymium (Nd) precursor, a promethium (Pm) precursor, a samarium (Sm) precursor, an europium (Eu) precursor, a gadolinium (Gd) precursor, a terbium (Tb) precursor, a dysprosium (Dy) precursor, a holmium (Ho) precursor, a ytterbium (Yb) precursor, a lutetium (Lu) precursor, and a combination thereof.
LiEr1-x-yLyF4:Tm3+x[Chemical Formula 1]

(In Chemical Formula 1, x is a real number satisfying 0≤x≤0.3, y is a real number satisfying 0≤y≤0.8 and is selected within a range satisfying 0≤x+y≤0.9, and L is a material of the first precursor and is any one selected from the group consisting of Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Lu, and a combination thereof.)

According to another aspect of the present invention, there is provided a polymer composite including the above-described fluoride nanophosphor.

According to another aspect of the present invention, there is provided a display device including the above-described fluoride nanophosphor.

According to another aspect of the present invention, there is provided a fluorescent contrast agent including the above-described fluoride nanophosphor.

According to another aspect of the present invention, there is provided an anti-counterfeiting film including the above-described fluoride nanophosphor.

According to another aspect of the present invention, there is provided a magnetic resonance imaging (MRI) contrast agent including the above-described fluoride nanophosphor.

