WO2007148880A1 - Thulium-containing fluorescent substance for white light emitting diode and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a thulium-containing fluorescent substance for a white light emitting diode represented by a following chemical formula 1, [Chemical Formula 1 ] (M1-X-J7EuxTnIy)2SiO4 where M is a divalent cation metal including Sr or Ba, with 0.005 < x < 0.05 and 0.005 < y < 0.05. The silicate-based yellow fluorescent substance according to the present invention is sufficiently excited by a blue light source generated by a blue LED to exhibit a yellow emission, with superior luminous intensity, due to the addition of europium oxide (Eu2O3) and thulium oxide (Tm2O3) as an activator, thereby being suitable for a white LED.

Description

THULIUM-CONTAINING FLUORESCENT SUBSTANCE FOR WHITE

LIGHT EMITTING DIODE AND MANUFACTURING METHOD THEREOF

[Technical Field]

The present invention relates to a thulium-containing fluorescent substance for a

white light emitting diode(LED) represented by a following chemical formula 1,

[Chemical Formula 1]

(Mi-_x-yEu_xTm_y)₂Si0₄

where M is a divalent cation metal including Sr or Ba, with 0.005<x<0.05 and

0.005<y<0.05.

Furthermore, the present invention is to provide a method of manufacturing a

fluorescent substance for a white light-emitting diode of the above chemical formula 1, that

is, for a yellow fluorescent substance, wherein a silicate-based compound is used as a host

material, the method comprising the steps of adding europium oxide (Eu₂O₃) and thulium

oxide (Tm₂O₃) to this substance and mixing them together; thermally treating a material

obtained in the mixing step in a temperature between 1,000-1,500 °C; and post-processing

including a pulverizing process.

[Background Art]

A white LED is one of next-generation light-emitting elements which can replace

the existing general lights, and the white light-emitting diode has been manufactured by mixing three-primary-colored light-emitting diodes since red, green and blue light-emitting

diodes having a high luminance began to be commercialized.

Due to a remarkable development of technology, a yellow fluorescent substance

can be excited by a blue light source having a wavelength of 460 nm using a blue light-

emitting diode having sufficient excited energy, and thus a white light-emitting diode can

be manufactured by mixing blue and yellow.

[Disclosure]

[Technical Problem]

However, in order to implement a white light-emitting diode having high

luminance, it is required to provide a yellow fluorescent substance having high luminance

excited by a blue light source generated from a blue light-emitting diode to emit a light.

[Technical Solution]

Accordingly, the present invention is made by taking the problem mentioned

above into consideration, and a silicate-based fluorescent substance activated by europium,

having low luminous efficiency, is doped by thulium as a co-activator under blue light

source excitation, thereby providing a thulium-containing fluorescent substance for a white

light emitting diode and a manufacturing method thereof to enhance light-emitting

efficiency even under blue light source excitation. [Advantageous Effects]

The silicate-based yellow fluorescent substance according to the present invention

is sufficiently excited by a blue light source generated by a blue LED to exhibit a yellow

emission, and especially the luminous intensity is superior, thereby having an effect

suitable for a white LED, and also an effect of superior yellow-emitting luminance can be

obtained by adding europium oxide (Eu₂O₃) and thulium oxide (Tm₂O₃) as an activator.

[Description of Drawings]

The above and other objects, features and advantages of the present invention will

become apparent from the following description of preferred embodiments given in

conjunction with the accompanying drawings, in which:

Fig. 1 is a scanning electronic microscopic view of a yellow fluorescent substance

obtained in an Example 2 of the present invention,

Fig. 2 is a luminous intensity graph in case where an amount of added europium is

changed in an Example 3 of the present invention,

Fig. 3 is a resultant emission spectrum graph in an Example 4 of the present

invention,

Fig. 4 is a luminous intensity graph for a white LED obtained in an Example 5 of

the present invention, and Fig. 5 is a resultant light excitation spectrum graph of a fluorescent substance

obtained in an Example 6 of the present invention.

[Best Mode]

Hereinafter, the embodiments of the present invention will be described in detail

with reference to accompanying drawings.

In order to achieve the above-mentioned object, the present invention is

characterized to provide a thulium-containing fluorescent substance for a white light

emitting diode represented by a following chemical formula 1,

[Chemical Formula 1]

(M_1-x-yEuχTm_y)₂Siθ₄

where M is a divalent cation metal including Sr or Ba, with 0.005<x<0.05 and

0.005<y<0.05.

Also, the present invention is to provide a method of manufacturing a yellow

fluorescent substance of the above chemical formula 1, characterized in that a silicate-

based compound is used as a parent substance, the method comprising the steps of adding

europium oxide (Eu₂O₃) and thulium oxide (Tm₂O₃) to this substance and mixing them

together; thermally treating a material obtained in the mixing step in a temperature

between 1,000-1,500 °C; and post-processing including a pulverizing process.

Furthermore, the present invention is to provide a thulium-containing fluorescent substance for a white light emitting diode, characterized in that the fluorescent substance is

represented by a following chemical formula 2,

[Chemical Formula 2]

(M_1-x-y._z-αEu_xTmyA_zR_α)₂Siθ₄

where M is a divalent cation metal including Sr or Ba, and A is a univalent cation

metal including Li or K with 0.00<z<0.05, and R is a rare earth metal including Ce, Pr, Sm

or Gd with 0.00<α<0.05.

The silicate-based yellow fluorescent substance according to the present invention

is sufficiently excited by a blue light source generated by a blue LED to exhibit a yellow

emission, and especially the luminous intensity is superior, thereby having an effect

suitable for a white LED.

According to the present invention, in particular, it is characterized to obtain an

effect of superior yellow-emitting luminance by adding europium oxide (Eu₂O₃) and

thulium oxide (Tm₂O₃) as an activator.

Such a yellow fluorescent substance according to the present invention will be

described in more detail as follows based on a manufacturing method thereof.

First, carbonate compound containing a divalent cation and silicon oxide (SiO₂) is

added by europium oxide (Eu₂O₃) as an activator and thulium oxide (Tm₂O₃) as a co-

activator to mix them.

At this time, 0.005-0.04 mol of the europium oxide, which is used as an activator, is added to a carbonate compound among fluorescent substance raw materials. There

occurs a problem that it may not be a sufficient amount to function as an activator if the

amount less than 0.005 mol is used, and the luminance may be reduced due to a

concentration quenching phenomenon if more than 0.04 mol is used.

According to the present invention, furthermore, thulium oxide, which is a co-

activator, is used together, and it will be an optimal amount when the molar ratio of Eu :

Tm is 0.03 : 0.01.

The fluorescent substance raw materials and co-activator as described above were

measured respectively to be a specific ratio according to a desired composition, and

sufficiently mixed to be a uniform composition using a mixer, such as balling milling or

agate mortar under ethanol solvent for an effective mixing. Then, the mixture was placed

into an oven and dried at a temperature between 100-150 °C for 24 hours. The dried

mixture was placed into a high-purity alumina boat and thermally treated at a temperature

between 1,000-1,300 °C using an electric furnace, and then sufficiently pulverized. If

thermal treatment temperature is higher than 1,300 ⁰C, there may be a problem that non¬

uniform growth of particles is caused due to an oversintering phenomenon to reduce the

luminance, and if lower than 1,000 ⁰C, it may be not good because the phase formation

property is inferior.

Photoluminescence (PL) was measured for this powder using a fluorescence

spectrophotometer, and as a result a yellow fluorescent substance represented by the chemical formula 1, having a maximum emission peak at 560 nm, showing a strong

emission spectrum in a range between 475-680 nm, and exhibiting a superior emission

luminance, was obtained.

In this way, the thulium-containing silicate-based yellow fluorescent substance

manufactured according to the present invention is excited by a blue light source generated

by a blue LED to exhibit a yellow emission having superior luminous intensity, thereby

having high luminance suitable for a white LED.

Hereinafter, it will be described in more detail through examples.

Example 1: Manufacture of Fluorescent Substance

(Sro.₇₅Bao.₂₁Euo.o3Tmo.o₁)₂Siθ4

With a ratio of 0.75 mol strontium carbonate, 0.21 mol barium carbonate, 0.03 mol

europium oxide, 0.01 mol thulium oxide, and 1 mol silicon oxide, raw materials were

measured to be mixed uniformly using an agate mortar. The mixed specimen is dried at

130 °C for 24 hours using an oven. The obtained mixture was placed into a high-purity

alumina boat and the electric furnace was heated at 1,300 °C for 4 hours in a reducing

atmosphere. The obtained material was placed into a distilled water and pulverized using

ultra waves and a mixer, and then ball-milled to obtain a yellow fluorescent substance

represented by (Sro_,75Bao.₂₁Euo_.o₃Tm₀.oi)2Siθ4. Example 2: Surface Shape of Silicate-Based Yellow Fluorescent Substance to

Which Europium and Thulium are Added

Similarly implemented as in the Example 1, but 0.76 mol of strontium carbonate

and 0.03 mol of europium oxide were added respectively to obtain a yellow fluorescent

substance represented by (Sro_.76Ba_0.21Euo_.02Tmo.oi)₂Si0₄. Then, the obtained yellow

fluorescent substance was observed by a scanning electronic microscope, and the surface

shape is shown in Fig. 1.

Fig. 1 is a scanning electronic microscopic view of the yellow fluorescent

substance obtained in an Example 2 of the present invention.

As shown in Fig. 1, it is confirmed that the silicate-based yellow fluorescent

substance according to the present invention is particles having a size of 10-30 μm.

Example 3: Photoluminescence Intensity of Silicate-Based Yellow Fluorescent

Substance according to the Europium Content

For a yellow fluorescent substance represented by (Sro._79-xBao_.2iEu_x)₂Siθ4,

photoluminescence was measured for the specimens in which an amount of added

europium has been changed, and the result is shown in Fig. 2.

As shown in Fig. 2, it is confirmed that emission luminance gradually increased by

adding europium to the yellow fluorescent substance of the invention, but emission

luminance decreased due to a concentration quenching phenomenon in case where an amount of added europium is more than 0.0035 mol. Accordingly, it is confirmed that a

range of added europium capable of exhibiting an especially superior emission luminance

is 0.025-0.035 mol.

Example 4: Comparison of Emission Spectrum of Fluorescent Substance

(Sro.₇₆Bao.₂iEuo.o₃)₂Si0₄ with Fluorescent Substance in Which Thulium is Added to

This Substance

Emission spectrum was measured for the fluorescent substance

(Sro_.76Ba_0.21Euo_.03)₂Siθ₄ obtained in the Example 3 and the fluorescent substance (Sro._76-

_yBa_0.21Euo_.o₃Tm_y)₂Siθ₄, and the result is shown in Fig. 3.

As shown in Fig. 3, as europium and thulium were added by 0.03 mol and 0.01

mol respectively, the yellow fluorescent substance according to the present invention

exhibits a yellow emission having a peak wavelength at 560 nm, and it is confirmed that

the yellow fluorescent substance has a superior emission luminance compared with an

emission spectrum of fluorescent substance (Sr_C76Ba_C21EUc_Os)₂SiO₄. Consequently, it is

confirmed that europium ion (Eu ) works as an activator on fluorescent substance

(Sro.₇₆Bao.₂₁Euo.₀₃)₂Si0₄ to exhibit a yellow emission, and thulium ion (Tm²⁺), which has

been added together with the europium ion, as a co-activator for transferring energy to the

europium ion, greatly contributes to a yellow emission of silicate fluorescent substance.

Since divalent thulium ion (Tm²⁺) is a material which is unstable at room temperature and in air as well as has a high oxidizing power, it has a tendency to be re-oxidized to trivalent

thulium ion (Tm³⁺) in silicate environment. Because oxidizing power at this time is greater

than the oxidizing power of europium ion from a divalent to a trivalent state, firstly

thulium is oxidized and this delays the oxidation of europium ion, thereby increasing the

lifetime as well as enhancing the stability of reduced europium ion due to this effect.

Furthermore, substitution, surface defect, or the like in europium are controlled to help its

crystal growth, and as a result it is expected to have an effect of increasing luminous

intensity.

Example 5: Manufacture of a White LED Using Fluorescent Substance

(SrC₇₅BaO_-21EUcOsTmO-Oi)₂SiO₄

Using fluorescent substance (Sro_.75Bao.₂₁Euo.o3Tmo.₀₁)₂Siθ4 obtained in the

Example 4, a white LED is manufactured, and the result is shown in Fig. 4.

As shown in Fig. 4, it is confirmed that the yellow fluorescent substance of the

invention exhibits a superior yellow emission at 560 nm in a blue excited light of 465 nm,

and the blue excited light and the yellow emission are combined to emit a white light.

Example 6: Manufacture of Fluorescent Substance

(SrO_-72BaO_-2IEUcOsTmCo₁LiCo₂GdO-Oi)ZSiO₄

In case of the Example 4, thulium exists as two types, both in divalent and trivalent state within a silicate fluorescent substance, and it increases lifetime and stability

when re-oxidizing from a divalent to a trivalent state. At this time, however, thulium

oxidized to a trivalent state may reduce luminous characteristics due to a charge valence

difference from strontium, which is a divalent cation. Accordingly, there may be a method

of adding univalent lithium for a method of reducing the charge quantity of thulium, which

has been re-oxidized to a trivalent state, again to a divalent state. Through transferring

electrons between thulium, which has been re-oxidized to a trivalent state, and univalent

lithium, the charge quantity of strontium, valium, europium, thulium, and lithium

consisting of a cationic group, is all controlled to a divalent level, thereby facilitating

energy transfer. Accordingly, through the site control, good crystal growth, and increased

energy transfer of europium by adding thulium and lithium in proportioning materials,

luminous intensity can be enhanced and the stability of lifetime and crystal can be induced.

Light excitation spectrum was measured for fluorescent substance

(Sro_.72Bao_.2iEuo_.o₃Tmo_.oiLio.o₂Gdo_.oi)₂Siθ₄ obtained in the Example 6 and

(Sro.₇₆Ba_0.21Euo.o₃)₂Si0₄ to which co-activators such as thulium or the like is not added, and

the result is shown in Fig. 5.

As shown in Fig. 5, it can be seen that the luminous intensity of fluorescent

substance (a) (Sr_C72Ba_C21EUoOsTm_CQ₁Li_O1O₂Gd_COi)₂SiO₄ increases more than 15 %

compared with fluorescent substance (b) to which a co-activator such as Tm or the like is

not added in vicinity of 450 nm, which is a blue LED light source. [Industrial Applicability]

As stated above, according to the present invention, by adding europium as an

activator and thulium as a co-activator to a silicate-based fluorescent substance, it has high

luminance as well as exhibits a yellow emission under excitation of a blue light source

having a wavelength of 460 nm generated from a blue LED, and therefore it is useful as a

yellow fluorescent substance applicable to fluorescent substance for a white LED.

Moreover, by adding lithium, it can prevent the variation of charge quantity caused by the

re-oxidation of thulium, and increase lifetime, thereby enhancing the overall stability of

crystal.

Claims

[CLAIMS] [Claim 1 ] A thulium-containing fluorescent substance for a white light emitting diode, characterized in that the fluorescent substance is represented by a following chemical formula 1,

[Chemical Formula 1]

(M _1-x-yEu_xTmy)₂ SiO₄

where M is a divalent cation metal including Sr or Ba with 0.005<x<0.05 and

0.005<y<0.05.

[Claim 2]

The thulium-containing fluorescent substance for a white light emitting diode

according to claim 1, characterized in that the europium oxide and thulium oxide are used

to become l≤x/y<5.

[Claim 3]

A method of manufacturing a thulium-containing fluorescent substance for a white

light emitting diode as a manufacturing method of claim 1, characterized in that a silicate-

based compound is used as a parent substance, the method comprising the steps of:

adding europium oxide (Eu₂O₃) and thulium oxide (Tm₂O₃) to this substance and mixing them together;

thermally treating a material obtained in the mixing step in a temperature between

1,000-1,500 °C; and

post-processing including a pulverizing process.

[Claim 4]

A thulium-containing fluorescent substance for a white light emitting diode,

characterized in that the fluorescent substance is represented by a following chemical

formula 2,

[Chemical Formula 2]

(M₁-_x-y-z-αEuχTm_yA_zR_α)₂Si0₄

where M is a divalent cation metal including Sr or Ba, and A is a univalent cation

metal including Li or K with 0.00<z<0.05, and R is a rare earth metal including Ce₅ Pr, Sm

or Gd with 0.00≤α<0.05.

[Claim 5]

A method of manufacturing a thulium-containing fluorescent substance for a white

light emitting diode as a manufacturing method of claim 4, characterized in that a silicate-

based compound is used as a parent substance, the method comprising the steps of:

adding europium oxide (Eu₂O₃), thulium oxide (Tm₂O₃), lithium carbonate (Li₂CO₃), and gadolinium oxide (Gd₂O₃) to this substance and mixing them together;

thermally treating a material obtained in the mixing step in a temperature between

1,000-1,500 ⁰C; and

post-processing including a pulverizing process.