WO2010024480A1

WO2010024480A1 - Red phosphor and forming method thereof for use in solid state lighting

Info

Publication number: WO2010024480A1
Application number: PCT/KR2008/004994
Authority: WO
Inventors: Sung-Sik Chang
Original assignee: Kangnung-Wonju National University Industry Academy Cooperation Group
Priority date: 2008-08-26
Filing date: 2008-08-26
Publication date: 2010-03-04
Also published as: KR101072576B1; TW201009050A; JP5583670B2; JP2012501365A; KR20110004915A

Abstract

There are described a red phosphor for use in solid state lighting and a method for preparing the same, which can be excited efficiently with near UV light, blue light and green light. The red phosphor for use in solid state lighting includes a La and Ti oxide as a main composition and a rare earth element as a subsidiary composition. The rare earth element includes a single element or one or more combination thereof selected from a group consisting of Eu, Er, Dy, Sm, Tb, Ce, Gd, Nd, Dy, and Ho. The La and Ti oxide may be one selected from a group consisting of La₂ TiO₅, LaTi₂ O₉ and La₄ Ti₉ O₂₄. The red phosphor of the present invention can be prepared by employing a solid state sintering method at an ambient air at atmospheric pressure and temperature range of 1,000 -1,50O⁰C, and thus is simple in preparing process to save cost.

Description

RED PHOSPHOR AND FORMING METHOD THEREOF FOR USE IN SOLID STATE LIGHTING

Technical Field

[1] The present invention relates to a red phosphor and it's forming method, and more particularly, to a red phosphor and it's forming method for use in solid state lighting. Background Art

[2] Generally, a white light LED using semiconductor devices has been recognized as a replacement light source for general lighting devices including a fluorescent lamp for home use and a LED backlight since the white light LED has characteristics such as long life, and could be more miniaturized and further can be driven by low power source comparing to an incandescent lamp such as a 6OW economical type-lamp.

[3] In a method for manufacturing the white light LED, it has been proposed to use light emitting diodes of all three colors (Red, Green and Blue); however, it has problems that manufacturing cost is high, and product size thereof becomes larger due to a complicate driving circuit. Meanwhile, a white light LED fabricated by combining a blue LED of InGaN semiconductor having 460nm wavelength with YAG: Ce phosphor has been realized up to now, wherein a portion of blue light emitted from a blue LED excites YAG:Ce phosphor to thereby generate fluorescence of yellow-green, and the portion of blue and the yellow-green are combined to thereby emit a white light.

[4] However, the emitted white light (generated by combining blue LED with YAG: Ce phosphor) has a narrow region of visible light spectrum (lack of red component) and thus a color rendering index is low. As a result, the color can not be expressed properly.

[5] In order to solve the aforementioned problems of the white light LED, various studies on developing white light LED emitting white light almost similar to natural color has been carried out by using Ultra Violet ("UV") LED as exciting light source and combining all of red, green and blue phosphors. Red luminescent material is to be developed essentially in order to fabricate this type of white light LED, which has excellent luminance at an exciting light source having 400nm wavelength and best device efficiency. That is, while green and blue phosphors have satisfactory luminance efficiencies, since red phosphor has very low luminance efficiency, red luminescent material having excellent luminance efficiency with respect to an UV excitation source has to be developed urgently.

[6] Additionally, the luminescent material having good luminance efficiency with respect to near UV excitation source is considered to be very important for developing an active luminescent LCD. The active luminescent LCD is configured such that the light emitted from a rear surface thereof penetrates into a liquid crystal layer through a polarizer, which allows backlight to pass or shield through its alignment properly so that the backlight forms a predetermined displaying type. In subsequent, the backlight passed through the liquid crystal layer excites a corresponding phosphor, thereby displaying images through a front glass. Even though this active luminescent LCD element is simple in structure and can be fabricated easily, comparing to an existing color liquid crystal display device, however, emission brightness of a red phosphor among the used phosphors is low so that it is considered not to be practical.

[7] In particular, the active luminescent LCD device has to utilize near UV (light) equal to or more than 390nm for protecting a liquid crystal as a rear surface light source, wherein a UV LED may be a best light source equal to or more than 390nm as the rear surface light source. As a result, development of red luminescent material having good luminance efficiency with respect to near UV is very important to develop an active luminescent LCD device as same as red and white LED.

[8] A conventional white light LED has been used by combining blue LED with

YAG:Ce phosphor. Since red color portion thereof is deficient, the emission light thereof displays a bluish white color. Furthermore, there arises problems that the red phosphor has low luminescent efficiency; and is deteriorated depending on time elapsed and temperature; and further excitation with respect to visible light may be impossible, etc.

[9] In order to solve the aforementioned problems, CaAlSiN as red phosphor has been developed. This red phosphor (CaAlSiN ) utilizes blue LED light source as an excitation light source, which is stable in a temperature range from room temperature to 100⁰C. Meanwhile, this red phosphor is made by mixing aluminum nitride, calcium nitride and europium nitride in a globe box shielded from air and moisture and then placing it at about 10 atmospheric pressures (in reducing atmosphere) and at about 1,800⁰C to prepare red phosphor of Eu solid solution. Here, the preparing method of red phosphor containing CaAlSiN is complicate and raw materials thereof are expensive; and the excitation efficiency of the red phosphor with respect to near UV is low.

Disclosure of Invention Technical Problem

[10] Accordingly, the object of the present invention is to provide a red phosphor for use in solid state lighting, which can be prepared in ambient air at atmospheric pressure and can be excited with anyone of a near UV, a blue light and a green light, and a method of preparing the same. Technical Solution

[11] In order to achieve the above object, in accordance with the present invention, a red phosphor for use in solid state lighting including a La and Ti oxide and a rare earth element is formed. In the present invention, the rare earth element may be a single element or one or more combination thereof selected from a group consisting of Eu, Er, Dy, Sm, Tb, Ce, Gd, Nd, Dy, and Ho. Eu can be representatively used as the rare earth element. In accordance with the present invention, there may be formed a red phosphor for use in solid state lighting prepared by mixing a La oxide, a Ti oxide and an Eu oxide in a predetermined mole fraction thereof. A red phosphor for use in solid state lighting in accordance with the present invention may be produced by employing a solid state sintering method in an ambient air at atmospheric pressure and temperature range of 1,000-1,500⁰C.

Advantageous Effects

[12] In a conventional red phosphor, there arise problems that since it is prepared in a nitrogen atmosphere, production utilities are complex; and cost thereof is expensive; and further the red phosphor can not be excited efficiently with UV. However, a red phosphor for use in solid state lighting in accordance with the present invention can be prepared in an ambient air at atmospheric pressure with low cost. The red phosphor for use in solid state lighting in accordance with the present invention may include a La and Ti oxide as a main element and a rare earth element as a subsidiary element and further can be excited with anyone of near UV, blue light and green light.

[13] The red phosphor for use in solid state lighting in accordance with the present invention has an advantage for improving color rendering index of a white LED and further has an excellent thermal stability. Brief Description of the Drawings

[14] The accompanying drawings, which are included to aid in understanding the invention and are incorporated into and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:

[15] Fig. 1 is a view showing an XRD diffraction pattern of La TiO red phosphor prepared in accordance with a first embodiment of the present invention;

[16] Fig. 2 is a view displaying luminance intensities of a La TiO red phosphor and a Y

O S excited with near UV of 395nm when the La TiO red phosphor is prepared in a mole ratio of La O TiO and Eu O being 0.8: 1.0:0.2 in accordance with the first

2 3, 2, 2 3 embodiment of the present invention; [17] Fig. 3 is a view representing luminance intensities of a La TiO red phosphor and a conventional Y O S red phosphor excited with blue LED light of 465nm when the La

2 2 2

TiO red phosphor is prepared in a mole ratio of La O TiO and Eu O being 0.8: 1.0:0.2 in accordance with the first embodiment of the present invention;

[18] Fig. 4 is a view illustrating luminance intensity of a La TiO red phosphor when the

La TiO red phosphor is prepared by varying addition amount (mixing mole ratio) of Eu O to respective 3 luminance peaks (594nm, 610nm, 628nm) case of being excited with near UV of 395nm in accordance with the first embodiment of the present invention;

[19] Fig. 5 is a view showing luminance intensity of a La TiO red phosphor when the

La TiO red phosphor prepared by varying addition amount (mixing mole ratio) of Eu O to the respective 3 luminance peaks (594nm, 610nm, 628nm) in case of being excited with blue light of 465nm in accordance with the first embodiment of the present invention;

[20] Fig. 6 shows excitation spectra of a La TiO red phosphor and a conventional phosphor of Y O S when the La TiO red phosphor is prepared in a mole ratio of La O TiO 2, and Eu 2 O 3 being 0.8: 1.0:0.2 in accordance with the first embodiment of the present invention; [21] Fig. 7 represents XRD diffraction patterns of LaTi O red phosphors prepared in accordance with a second embodiment of the present invention; [22] Fig. 8 views luminance intensities of a LaTi O red phosphor and a conventional Y

O S phosphor excited with a near UV of 395nm when the LaTi O red phosphor is prepared in a mole ratio of La O : TiO : Eu O being 0.8:2.0:0.2 in accordance with the

2 3 2 2 3 second embodiment of the present invention;

[23] Fig. 9 illustrates luminance intensities of a LaTi O red phosphor and a conventional

Y O S phosphor excited with blue LED light of 465nm when the LaTi O red phosphor prepared in a mole ratio of La O : TiO : Eu O being 0.8:2.0:0.2 in accordance with the

2 3 2 2 3 second embodiment of the present invention; [24] Fig. 10 provides luminance intensities of a LaTi O red phosphor excited with near

UV of 395nm when the LaTi O red phosphor is prepared by varying addition amount

(mixing mole ratio) of Eu O in accordance with the second embodiment of the present invention; [25] Fig. 11 views luminance intensities of a LaTi O red phosphor excited with blue

2 9

LED light of 465nm when the LaTi O red phosphor is prepared by varying addition amount (mixing mole ratio) of Eu O in accordance with the second embodiment of the present invention;

[26] Fig. 12 is a view showing excitation spectra of a LaTi O red and a conventional Y

O S phosphor when the LaTi O red phosphor is prepared by mixing La O TiO Eu O in a mixing ^to mole ratio of La 2 O 3, TiO 2, Eu 2 O 3 being ^to 0.8:2.0:0.2 in accordance with the second embodiment of the present invention;

[27] Fig. 13 represents an XRD diffraction pattern of a La Ti O red phosphor when the

La 4 Ti9 O 24 red r phos fphor is r prerpared by J mixing ^to La 2 O 3, TiO 2, Eu 2 O3 in a mole ratio

(optimal mixing mole ratio) of 0.8:3.0:0.2 and by heating it in accordance with a third embodiment of the present invention; [28] Fig. 14 shows luminance intensities of a La Ti O red phosphor and a conventional

^& 4 9 24 ^{r r}

Y O S red phosphor excited with near UV of 395nm when the La Ti O red phosphor

2 2 4 9 24 is prepared in an optimal mixing mole ratio (ratio of La O TiO Eu O being 0.8:3.0:0.2) in accordance with the third embodiment of the present invention; [29] Fig. 15 illustrates luminance intensities of a La Ti O red phosphor and a con-

4 9 24 ventional Y O S red phosphor excited with blue light of 465nm when the La Ti O red

2 2 4 9 24 phosphor is prepared in an optimal mixing mole ratio (ratio of La O TiO Eu O being 0.8:3.0:0.2) in accordance with the third embodiment of the present invention;

[30] Fig. 16 provides luminance intensities of a La Ti O red phosphor excited with near

UV of 395nm when the La Ti O red phosphor is prepared depending on varying addition amount (mixing mole ratio) of Eu O in accordance with the third embodiment of the present invention;

[31] Fig. 17 represents luminance intensities of a La Ti O red phosphor excited with blue light of 465nm when the La Ti O red phosphor is prepared depending on varying addition amount (mixing mole ratio) of Eu O in accordance with the third embodiment of the present invention;

[32] Fig. 18 views luminance intensities of a La Ti O red phosphor when the La Ti O

4 9 24 4 9 24 red phosphor is prepared by mixing La O TiO and Eu O in a mole ratio of La O TiO Eu O being 0.8:3.0:0.2 depending on heat treatment temperatures; [33] Fig. 19 shows excitation spectra of a La Ti O red phosphor and a conventional Y

^{& r} 4 9 24 ^{r r} 2

O S red phosphor when the La Ti O red phosphor is prepared in a mole ratio of La O

2 4 9 24 2 3,

TiO Eu O being 0.8:3.0:0.2 (that is, optimal mixing mole ratio of Eu O ) in accordance with the third embodiment of the present invention;

[34] Fig. 20 depicts excitation spectra of La-Ti oxide red phosphor's and a conventional

Y O S red phosphor when each of the La-Ti oxide red phosphor's is prepared in a corresponding optimal mole fraction of Eu O in accordance with a corresponding preferred embodiment of the present invention;

[35] Fig. 21 views luminance intensities of La-Ti oxide red phosphor's and a conventional Y O S red phosphor excited with near UV of 395nm when each of the La-Ti oxide red phosphor's is prepared in a corresponding optimal mole fraction of Eu O in accordance with a corresponding preferred embodiment of the present invention; and

[36] Fig. 22 represents luminance intensities of La-Ti oxide red phosphor's and a conventional Y O S red phosphor excited with blue light of 465nm when each of the La-Ti oxide red phosphor's are prepared in a corresponding optimal mole fraction of Eu O in accordance with a corresponding preferred embodiment of the present invention. Best Mode for Carrying Out the Invention

[37] In accordance with a preferred embodiment of the present invention, red phosphor including a La and Ti oxide (hereinafter, may be also referred to as "La-Ti oxide") may be prepared by mixing a La oxide, a Ti oxide and an Eu oxide in an optimal mole fraction and heating to temperature range of 1,000-1,500⁰C in an ambient air at atmospheric pressure in order to overcome the aforementioned problems in the prior art. Here, a La and Ti oxide refers to a compound containing La, Ti and oxygen(O) as chemical elements such as La 2 TiO5 , LaTi 2 O9 , La4 Ti9 O 24 , which is re ^rpresented as La x Tiy

O . z

[38] Hereinafter, red phosphor's for use in solid state lighting prepared in accordance with preferred embodiments of the present invention are mainly described about such as red phosphor's for use in white light LED'S. However, it should be noted that the red phosphor's for use in solid state lighting prepared in accordance with preferred embodiments of the present invention are not limited to the red phosphor's for use in white LED's, but also can be applied to various fields.

[39] Additionally, while there is described that Eu is used as a representative rare earth element in the embodiments of the present invention, a person who has an ordinary skill in the art to which the invention pertains may choose other rare earth elements in stead of Eu. That is, a rare earth element may be selected from a group consisting of Eu, Er, Dy, Sm, Tb, Ce, Gd, Nd, Dy, and Ho as a single element or one or more combination thereof. Mode for the Invention

[40] [First embodiment] Prep earing a red p ehosp ehor of La ^ TiO _L :Eu

[41] Slurry formed by mixing proper amount of raw materials of La O , TiO and Eu O with alcohol solvent using a mortar is mixed until the alcohol is vaporized. Alternatively, the raw materials may be weighted in a stoichiometric ratio and mixed to an alcohol solvent using an yttria stabilized zirconia balls. Thereafter, the raw materials mixed well in the alcohol solvent is ball milled for 24 hours, and then dried at an oven of 95⁰C and in turn, mixed in a mortar to be formed as a pellet or powder. In subsequent, the raw materials is heated to temperature range of 1,000-1,500⁰C at an ambient air at atmospheric pressure. At this time, the mixing of Eu O is performed varying a fraction thereof to a total of the raw materials from 0.005 to 0.4.

[42] Table 1 shows a mole ratio of mixing ^to amount of La 2 O 3 , TiO 2 and Eu 2 O 3 when TiO 2 is 1.0 mole and a mixing fraction of Eu O at each mixing ratio in accordance with a first embodiment of the present invention. [43] [44] Table 1 Mixing mole ratio of raw materials when preparing La TiO :Eu red phosphor

[45] [46] An optimal mixing fraction of Eu O has been found during variations of the mixing fractions. Here, the optimal mixing fraction refers to a mixing fraction of Eu O which maximizes luminance intensity of the red phosphor, which is used through the present whole specification as the same meaning.

[47] Fig. 1 is a view showing XRD diffraction pattern of a La TiO red phosphor (that is, oxides of Li and Ti is a type of La TiO ) prepared by mixing La O , TiO and Eu O in a mixing mole ratio of La 2 O3 TiO2 Eu2 O3 being 0.8:1.0:0.2 and then heating it.

Referring to Fig.l, it is shown that a single phase of La TiO is formed substantially. In Fig.1 08 1 02 next to LTE indicates a mixing mole fraction of La 2 O 3 , TiO2 and Eu2 O3

(0.8:1.0:0.2), wherein it is the same aspect as in Figs. 7, 13, 14 and 15.

[48] Observation of luminance spectrum [49] Fig. 2 is a view displaying luminance intensities of a La TiO red phosphor and a Y O S excited with near UV of 395nm when the La TiO red phosphor is prepared in a mole ratio of La O TiO and Eu O being 0.8: 1.0:0.2 in accordance with the first

2 3, 2, 2 3 embodiment of the present invention. Fig. 3 is a view representing luminance intensities of a La TiO red phosphor and a conventional Y O S red phosphor excited with blue LED light of 465nm when the La TiO red phosphor is prepared in an optimal mixing mole fraction of Eu O (La O TiO and Eu O = 0.8:1.0:0.2) in r^& 2 3 2 3, 2, 2 3 accordance with the first embodiment of the present invention.

[50] Referring to Fig. 2, it is shown that the maximum value of luminance intensity of the red phosphor prepared at the optimal mixing ratio through an experiment of the first embodiment obtained by being excited with near UV of 395nm is smaller than that of Y O S. However, it is shown in Fig. 3 that the luminance intensity of the red phosphor prepared at the optimal mixing ratio in accordance with the first embodiment is far greater than that of Y O S when being excited with blue light of 465nm.

[51] Referring to Figs. 2 and 3, three luminance peak values such as 594nm, 610nm and

628nm are found for the La TiO red phosphor prepared at the optimal mixing mole fraction of Eu O in accordance with the first embodiment of the present invention. Here, as shown in Figs. 2 and 3, 0.1 value is derived based on the experimental results shown in Figs. 4 and 5 as an optimal mixing mole fraction of Eu O (corresponding to 0.2 value of mixing mole ratio of Eu O ).

[52] Observation of the optimal mixing mole fraction of Eu O_

[53] Fig. 4 is a view illustrating luminance intensity of a La TiO red phosphor when the

La TiO red phosphor is prepared by varying addition amount (mixing mole ratio) of Eu O to respective 3 luminance peaks (594nm, 610nm, 628nm) when being excited with near UV of 395nm in accordance with the first embodiment of the present invention. Fig. 5 is a view showing luminance intensity of a La TiO red phosphor when the La TiO red phosphor prepared by varying addition amount (mixing mole ratio) of Eu O to the respective 3 luminance peaks (594nm, 610nm, 628nm) in case of being excited with blue light of 465nm in accordance with the first embodiment of the present.

[54] As shown in Figs. 4 and 5, it is observed that the optimal mixing mole ratio of Eu O allowing luminance intensity of the La TiO red phosphor to be maximum is 0.2 (corresponding mole fraction of Eu O to total raw materials is 0.1) at any cases of being excited with near UV of 395nm or blue light of 465nm. That is, the optimal mixing ratio of Eu O is about 0.2. In this case, the luminance intensity thereof is decreased at concentrations of no less than 0.2 due to an excessive concentration and no more than 0.2 due to deficient concentration of an activator, respectively. Meanwhile, the optimal heat treatment temperature is about 1,47O⁰C in cases of Figs. 4 and 5.

[55] Observation of excitation spectrum

[56] Fig. 6 shows excitation spectra of a La TiO red phosphor and a conventional phosphor of Y O S when the La TiO red phosphor is prepared in a mole ratio of La O TiO and Eu O being 0.8:1.0:0.2 (that is, mixed at an optimal mixing mole ratio) in accordance with the first embodiment of the present invention. Referring to Fig. 6, it has been observed that the red phosphor prepared at the optimal mixing mole ratio has smaller excitation peak with respect to near UV, and greater excitation peak with respect to blue LED light of 465nm in comparison with a conventional Y O S red phosphor.

[57] [58] [Second embodimentl Preparing red phosphor of LaTi O :Eu

2. 2. [59] Raw materials of La O TiO and Eu O is mixed at stoichiometric ratio to prepare a

2 3, 2, 2 3 red phosphor of LaTi O (that is, a red phosphor, wherein a Li and Ti oxide is represented as a type of LaTi O ) for use in solid state lighting including mainly a La- Ti oxide and containing Eu as a rare earth element.

[60] Slurry formed by mixing proper amount of raw materials of La O , TiO and Eu O with alcohol solvent in a mortar is mixed until the alcohol was vaporized. Alternatively, the raw materials may be weighted in a stoichiometric ratio and mixed to alcohol solvent using an yttria stabilized zirconia balls. Thereafter, the raw materials mixed well in alcohol solvent is ball milled for 24 hours, and then dried at an oven of 95⁰C and then mixed in a mortar to be formed as a pellet or powder. And then, the raw materials are heated to temperature range of 1,000-1,500⁰C at and ambient air at atmospheric pressure. At this time, the mixing of Eu O is performed varying a fraction thereof to a total of raw materials from 0.0033 to 0.267. Table 2 shows a mole ratio of mixing ^to amount of La 2 O 3 , TiO2 and Eu2 O3 when TiO 2 is 1.0 and a mixing ^to fraction of Eu 2

O at each mixing ratio in accordance with a second embodiment of the present invention.

[61] [62] Table 2 Mixing mole ratio of raw materials when preparing LaTi O :Eu phosphor

[63] [64] Fig. 7 represents XRD diffraction patterns of LaTi O red phosphors prepared in accordance with a second embodiment of the present invention. Referring to Fig.7, it is shown that a single phase of LaTi O is formed substantially when the mixing mole ratio of La 2 O3 , TiO 2 and Eu 2 O3 is 0.8:2.0:0.2( ^yLTE — 08 — 2 — 02) ^/ and

0.5:2.0:0.5(LTE_05_2_05). Here, it should be noted that single phase of LaTi O compound is obtained from 0.0033 to 0.1667 of mixing fraction of Eu O

[65] Observation of luminance spectrum

[66] Fig. 8 views luminance intensities of a LaTi O red phosphor and a conventional Y

O S phosphor excited with a near UV of 395nm when the LaTi O red phosphor is prepared in a mole ratio of La O : TiO : Eu O =0.8:2.0:0.2 in accordance with the

2 3 2 2 3 second embodiment of the present invention. Fig. 9 illustrates luminance intensities of a LaTi O red phosphor and a Y O S excited with blue LED light of 465nm when the

2 9 2 2

LaTi O red phosphor prepared in a mole ratio of La O : TiO : Eu O =0.8:2.0:0.2 in

2 9 2 3 2 2 3 accordance with the second embodiment of the present invention.

[67] The maximum value of luminance intensity for the LaTi O red phosphor prepared at the optimal mixing mole ratio in the second embodiment, obtained by being excited with near UV of 395nm is similar to that of Y O S, however, taking into consideration of luminance area, it shows far stronger luminance intensity than that of the conventional Y O S phosphor. When utilizing the blue LED of 465nm as an exciting light source, it is shown that the luminance intensity of LaTi O red phosphor prepared at the optimal mixing mole ratio in the second embodiment, as shown in Fig. 9, is greater than that of Y 2 O 2 S.

[68] Observance of the optimal mixing mole fraction of Eu O_

[69] Fig. 10 provides luminance intensities of a LaTi O red phosphor excited with near

UV of 395nm when the LaTi O red phosphor prepared by varying addition amount (mixing mole ratio) of Eu O in accordance with the second embodiment of the present invention. Fig. 11 views luminance intensities of a LaTi O red phosphor excited with blue LED light of 465nm when the LaTi O red phosphor prepared by varying addition amount (mixing mole ratio) of Eu O in accordance with the second embodiment of the present invention.

[70] As shown in Figs. 10 and 11, the optimal mixing ratio of Eu O is 0.2 (a corresponding fraction of Eu O to a total of raw material is 0.067) and further the luminance intensity thereof is decreased at concentrations of no less than 0.2 due to an excessive concentration and no more than 0.2 due to deficient concentration of an activator, respectively. Meanwhile, the optimal heat treatment temperature is about 1,44O⁰C in cases of Figs. 10 and 11.

[71] Observation of excitation spectrum

[72] Fig. 12 is a view showing excitation spectra of a LaTi O red and a conventional Y

O S red phosphor when the LaTi O red phosphor is prepared by mixing La O TiO Eu 2 O3 at an optimal mixing mole ratio of La 2 O3 TiO2 Eu2 O3 being 0.8:2.0:0.2 in accordance with the second embodiment of the present invention. Referring to Fig. 12, it is observed that LaTi O red phosphor prepared at the optimal mixing mole ratio has a greater excitation peak on near UV of 395nm and blue LED light of 465nm, comparing to the conventional Y O S red phosphor used for UV phosphor.

2 2

[73] [74] [Third embodiment] Preparing red phosphor of La Ti O :Eu

± a. ^'24. [75] Slurry formed by mixing proper amount of raw materials of La O , TiO and Eu O with alcohol solvent in a mortar is mixed until the alcohol is vaporized. Alternatively, the raw materials may be weighted at stoichiometric ratio and mixed to alcohol solvent using yttria stabilized zirconia balls. Thereafter, the raw materials mixed well in alcohol solvent is ball milled for 24 hours, and then dried at an oven of 95⁰C and mixed in a mortar to be formed as a pellet or powder. And then, the raw materials are heated to temperature range of 1,000-1,500⁰C at an ambient air at atmospheric pressure. At this time, the mixing of Eu O is performed varying a fraction thereof to a total of raw materials from 0.0025 to 0.2. Table 3 shows a mole ratio of mixing amount of La O , TiO and Eu O when TiO is 3.0 and a mixing fraction of Eu O at each

2 3 2 2 3 2 2 3 mixing ratio according to a third embodiment of the present invention.

[76] [77] Table 3 Mixing mole ratio of raw materials when preparing La Ti O :Eu phosphor

[78] [79] Fig. 13 presents an XRD diffraction pattern of a red phosphor when the La Ti O red phosphor is prepared by mixing La O TiO Eu O in a mole ratio (optimal mixing mole ratio) of 0.8:3.0:0.2 and by heating it in accordance with a third embodiment of the present invention. Referring to Fig.13, it is shown that a single phase of the La Ti O is formed substantially when the mixing mole ratio of La O , TiO and Eu O is 0.5:3.0:0.5(LTE_05_3_05) and 0.8:3.0:0.2 (LTE_08_3_02). Here, it should be noted that single phase of La4Ti9O24 compound is obtained from 0.0025 to 0.125 of mixing fraction of Eu O

2 3 [80] Observation of luminance spectrum

[81] Fig. 14 shows luminance intensities of a La Ti O and a conventional Y O S red

^& 4 9 24 2 2 phosphor excited with near UV of 395nm when the La Ti O is prepared in an optimal mixing mole ratio (ratio of La O TiO Eu O is 0.8:3.0:0.2) in accordance with the

^& 2 3, 2, 2 3 third embodiment of the present invention. Fig. 15 illustrates luminance intensities of a La Ti O red phosphor and a conventional Y O S red phosphor) excited with blue

4 9 24 ^{r r} 2 2 ^{r r} light of 465nm when the La Ti O red phosphor is prepared in an optimal mixing mole ratio (ratio of La O TiO Eu O is 0.8:3.0:0.2 in accordance with the third embodiment

2 3, 2, 2 3 of the present invention. [82] In Figs. 14 and 15, LTE_08_3_02 indicates a luminance spectrum of the red phosphor prepared in an optimal mixing fraction of Eu O in accordance with the third embodiment of the present invention. The luminance magnitude of the La Ti O red

4 9 24 phosphor excited with near UV and blue LED light when the La Ti O red phosphor

4 9 24 prepared at the optimal mixing ratio is far greater than that of the prior art red phosphor

[83] Observation of the optimal mixing mole fraction of Eu O 2. — 3

[84] Fig. 16 provides luminance intensities of a La Ti O red phosphor excited with near

UV of 395nm when the La Ti O red phosphor is prepared depending on varying addition amount (mixing mole ratio) of Eu O in accordance with the third embodiment of the present invention. Fig. 17 represents luminance intensities of a La Ti O red phosphor excited with blue light of 465nm when the La Ti O red phosphor is prepared depending on varying addition amount (mixing mole ratio) of in accordance with the third embodiment of the present invention.

[85] Referring to Figs. 16 and 17, the optimal mixing amount (mixing mole ratio) of Eu

O is 0.2 (a corresponding fraction of Eu O to a total of raw material is 0.05), and further the luminance intensity thereof is decreased at concentrations of no less than 0.2 due to an excessive concentration and no more than 0.2 due to deficient concentration of an activator, respectively.

[86] Fig. 18 views luminance intensities of a La Ti O red phosphor when the La Ti O

^& 4 9 24 ^{r r} 4 9 24 red phosphor is prepared by mixing La O TiO and Eu O in a mole ratio of La O

2 3, 2, 2 3 2 3,

TiO Eu O being 0.8:3.0:0.2 depending on heat treatment temperatures. Meanwhile, the optimal heat treatment temperature is about 1,34O⁰C in cases of Figs. 16 and 17.

[87] Observation of excitation spectrum

[88] Fig. 19 shows excitation spectra of a La Ti O red phosphor and a conventional Y

O 2 S red phosphor when the La 4 Ti9 O 24 red phosphor is prepared in a mole ratio of La 2 O3

TiO Eu O being 0.8:3.0:0.2 (that is, optimal mixing mole ratio of Eu O ) in accordance with the third embodiment of the present invention. Referring to Fig. 19, it is observed that the La Ti O red phosphor prepared at the optimal mixing mole ratio has greater excitation peak value on near UV of 395nm and blue LED light of 465nm, comparing to the conventional Y O S red phosphor. In Fig. 19, LTE_1_3_614 nm indicates a luminance spectrum (measured at the maximum value of 614nm) of the red phosphor prepared in an optimal mixing fraction of Eu O in accordance with the third embodiment of the present invention.

[89] Hereinafter, based on the results of the first to third embodiment as aforementioned, descriptions will be made referring to Figs. 20 to 22. Fig. 20 depicts excitation spectra of La-Ti oxide red phosphor's and a conventional Y O S red phosphor when each of the La-Ti oxide red phosphor's is prepared in a corresponding optimal mole fraction of Eu O in accordance with each of the first to third embodiments of the present invention.

[90] In Fig. 20, LTE_l_l_610 nm indicates an excitation spectrum (measured at the maximum value of 610nm) of the red phosphor prepared in an optimal mixing fraction of Eu 2 O 3 in accordance with the first embodiment; LTE 1 2 614nm indicates an excitation spectrum (measured at the maximum value of 614nm) of the red phosphor prepared in an optimal mixing fraction of Eu O in accordance with the second embodiment; and LTE_1_3_614 nm indicates an excitation spectrum (measured at the maximum value of 614nm) of the red phosphor prepared in an optimal mixing fraction of Eu 2 O 3 in accordance with the third embodiment.

[91] In Fig. 20, a horizontal axis indicates a wavelength of photo-luminescence; and a vertical axis indicates intensity of photo-luminescence thereof. The red phosphors in accordance with the embodiments of the present invention, as shown in Fig. 20, can be excited efficiently with any one of near UV, blue light and green light. Referring to Fig. 20, excitation spectra of the red phosphors including mainly a La-Ti oxide and prepared in optimal mixing fractions of Eu O in accordance with the first embodiment(LTE_l_l), second embodiment(LTE_l_2) and third embodiment(LTE_l_3) are compared to an excitation spectrum of a prior art Y O S which has been used as a red phosphor of UV excitation for a prior fluorescent lamp.

[92] As shown in Fig. 20, the spectrum of the prior art Y O S has mainly excitation band on UV region, and has far smaller excitation band on visible light region than that of the red phosphor of the present invention. Accordingly, the prior art Y O S can not be excited effectively on blue light and green light regions. The red phosphor including mainly a La-Ti oxide in accordance with the present invention has higher excitation intensity than that of the prior art Y O S red phosphor in any one region of near UV, blue light and green light.

[93] Fig. 21 views luminance intensities of La-Ti oxide red phosphor's and a conventional Y 2O 2S red r phos rphor excited with near UV of 395nm when each of the La-Ti oxide red phosphor's is prepared in a corresponding optimal mole fraction of Eu O in accordance with each of the first embodiment(LTE_l_l), second embodiment(LTE_l_2)(In Fig. 21, PL indicates luminescence intensity). As shown in Fig. 21, it is clear that the luminescence intensity of a La-Ti oxide red phosphor prepared in accordance with the embodiments of the present invention is three times greater than that of the conventional Y O S red phosphor which has been used as a red phosphor for a prior art fluorescent lamp.

[94] Fig. 22 represents luminance intensities of La-Ti oxide red phosphor's and a conventional Y O S red phosphor excited with blue light of 465nm when each of the La-Ti oxide red phosphor's are prepared in a corresponding optimal mole fraction of Eu O in accordance with each of the first embodiment(LTE_l_l), second embodiment(LTE_l_2) and third embodiment(LTE_l_3) of the present invention(In Fig. 22, PL indicates luminescence intensity).

[95] Referring to Fig. 22, it is cleat that the luminescence intensity of a La-Ti oxide red phosphor prepared in accordance with the embodiments of the present invention is about eleven times greater than that of the prior art Y O S red phosphor, and the La-Ti oxide red phosphor can be excited efficiently with the blue light. Here, it should be noted that one or more of near UV, blue light and green light source may be a phosphor.

[96] As aforementioned, various embodiments of preparing a red phosphor for use in solid state lighting including a La oxide and a Ti oxide as a main element and a rare earth element (such as Eu) as a subsidiary element are described in detail.

[97] Meanwhile, in accordance with another aspect of the present invention, a red phosphor for use in solid state lighting including a La and Ti oxide as a main element can be also prepared from raw materials such as chloride, nitride, sulfide and hydroxide of La and Ti. In this case, chloride, nitride, sulfide and hydroxide of La and/ or Ti may be mixed with each other together with a proper raw material of a rare earth element and then heat treated.

[98] In the course of such a process, each of chloride, nitride, sulfide and hydroxide of

La and/or Ti is dissociated through thermal heat treatment and La and Ti are combined each other with oxygen(O) to thereby form a La-Ti oxide red phosphor including a La and Ti oxide as main composition and a rare earth element (such as Eu) as a subsidiary composition. More detailed description thereof is omitted since the person with ordinary skill in the art can design variously the process referring to the first to third embodiments of the present invention.

[99] While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

[I] A red phosphor for use in solid state lighting comprising: a La and Ti oxide; and a rare earth element.

[2] The red phosphor for use in solid state lighting according to claim 1, wherein the rare earth element includes a single element or one or more combination thereof selected from a group consisting of Eu, Er, Dy, Sm, Tb, Ce, Gd, Nd, Dy, and Ho.

[3] The red phosphor for use in solid state lighting according to claim 1, wherein the

La and Ti oxide is one of La 2 TiO 5 , LaTi 2 O 9 and La 4 Ti 9 O 24.

[4] The red phosphor for use in solid state lighting according to claim 1, wherein the red phosphor can be excited with anyone of near UV light, blue light and green light. [5] The red phosphor for use in solid state lighting according to claim 1, wherein the red phosphor is prepared by employing solid state sintering method at an ambient air at atmospheric pressure and temperature range of 1,000-1,500⁰C. [6] The red phosphor for use in solid state lighting according to claim 1, wherein the red phosphor is used for a white light LED. [7] The red phosphor for use in solid state lighting according to claim 2, wherein the rare earth element is Eu. [8] The red phosphor for use in solid state lighting according to claim 3, wherein the red phosphor is formed by mixing a La oxide, a Ti oxide and an Eu oxide as raw materials in a predetermined mole fraction. [9] The red phosphor for use in solid state lighting according to claim 4, wherein at least one light source of the near UV light, blue light and green light is a phosphor. [10] The red phosphor for use in solid state lighting according to claim 8, wherein the

La oxide is La O , Ti oxide is TiO , and Eu oxide is Eu O and a mixing mole fraction of Eu 2 O 3 to a total of Eu 2 O 3 TiO 2 , and Eu 2 O 3 is 0.05 to 0.4.

[I I] A red phosphor for use in solid state lighting comprising: La and Ti oxide as main element; and a rare earth element; wherein the red phosphor is prepared by mixing one or more of chloride, nitride, sulfide and hydroxide of La and/or Ti and a raw material of a rare earth element and then heating at an ambient air at atmospheric pressure.

[12] The red phosphor for use in solid state lighting according to claim 11, wherein the red phosphor is prepared by employing a solid state sintering method in an ambient air at atmospheric pressure and temperature range of 1,000-1,500⁰C.