JPH07110945B2 - Terbium activated rare earth tantalum-based complex oxide phosphor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a phosphor, and more particularly to improvement of a terbium (Tb) -activated rare earth tantalum-based composite oxide phosphor that exhibits high-intensity green light emission under X-ray excitation. .

[Conventional technology]

A phosphor obtained by activating a rare earth tantalate salt with niobium (Nb) or thulium (Tm) emits blue light with high brightness when excited by X-rays.
Tb-activated phosphors are known to emit Tb-specific green emission under X-ray excitation (Journal of Luminescenc
e magazine, vol. 3, page 109 (1970), JP-B-58-22063, JP-A-62-58244, JP-A-62-246988, etc.).

By the way, the Nb-activated rare earth tantalate phosphor has already been put into practical use as a blue light emission intensifying screen used in combination with a regular type X-ray film. However Tb
Regarding the intensifying screen using the activated rare earth tantalate phosphor in the phosphor layer, although the photographic image quality is good when it is subjected to X-ray photography in combination with the orthotype X-ray film, It has not yet been put to practical use due to the drawback of low sensitivity (light conversion efficiency), and therefore various methods for improving the emission brightness of Tb-activated rare earth tantalate phosphors under X-ray excitation. Is being made. The present applicant also previously composition formula as more high-brightness green-emitting phosphor than Tb-activated rare earth tantalate hydrochloric phosphor _{(Ln 1-X Tb X)} 2 O 3 · mTa 2 O 5 · wB 2 O 3 (Tatashi, Ln is Y, La, G
at least one element selected from d and Lu,
x, m and w are respectively 5 × 10 ⁻⁴ ≦ x ≦ 0.1, 0.95 ≦ m ≦
The numbers satisfy the conditions of 1.05 and 0.01 <w ≦ 5.0. ), A phosphor in which a complex oxide of a rare earth tantalate salt and boron oxide (B ₂ O ₃ ) is used as a matrix, and this is activated by Tb (Japanese Patent Application No. 62-176010), Further development of a high brightness Tb activated rare earth tantalate phosphor is desired.

[Problems to be Solved by the Invention]

The present inventors have aimed to provide a phosphor that emits green light with high brightness particularly under X-ray excitation, as compared with the conventional Tb-activated rare earth tantalum phosphor, and the Tb-activated rare earth tantalum phosphor. Tb activation as a result of various studies on the relationship between the kind and amount of the element that is necessarily accompanied as an additive or an impurity to be added to the acid salt phosphor and the emission brightness of the obtained phosphor under X-ray excitation. The composition of the rare earth tantalate phosphor and the composition formula previously proposed by the applicant are ((Ln _1-X , Tb _X ) ₂ O ₃ · mTa ₂ O ₅ · wB
₂ O ₃ (however, Ln, x, m, and w are the same as above) represented by the Tb-activated composite oxide phosphor (these Tb-activated rare earth tantalate phosphors and the Tb-activated composite oxide). In the present specification, the oxide phosphors are collectively referred to as “Tb-activated rare earth tantalum-based composite oxide phosphors”), and in the description, niobium (Nb) and / or manganese (Mn) which are associated impurity elements are included.
It has been found that the layer relationship between the content of P and the emission brightness of the phosphor is particularly remarkable. Since Nb and Mn are the constituent elements of the raw material ore of Ta (columbite, tantalum, etc.), Nb is usually contained in the commercially available Ta compound used as the raw material of the rare earth tantalum-based complex oxide phosphor. Although it contains 100 ppm or more and Mn of several tens of ppm or more, Tb-activated rare earth tantalum can be obtained by purifying such a commercially available Ta compound and using a Ta compound having a smaller Nb and / or Mn content. The present inventors have found that the emission brightness of the system-based composite oxide phosphor can be remarkably improved as compared with the conventional one, and have completed the present invention.

Tb-activated rare earth tantalate-based composite oxide phosphor of the present invention [Means for Solving the Problems] The compositional formula _{(Ln 1-X, Tb X} ) 2 O 3 · mTa 2 O · nB 2 O 3 ( where , Ln is at least one element selected from Y, La, Gd and Lu, and m, n and x are each 0.95 ≦
It is a number satisfying the conditions of m ≦ 1.05, 0 ≦ n ≦ 5.0 and 5 × 10 ⁻⁴ ≦ x ≦ 0.1. ) And the Nb content is 50 ppm or less.

Further Tb-activated rare earth tantalate-based composite oxide phosphor of the present invention the composition formula _{(Ln 1-X, Tb X} ) 2 O 3 · mTa 2 O 5 · nB 2 O 3 ( where, Ln is Y, La, It is at least one element selected from Gd and Lu, and m, n and x are each 0.95 ≦
It is a number satisfying the conditions of m ≦ 1.05, 0 ≦ n ≦ 5.0 and 5 × 10 ⁻⁴ ≦ x ≦ 0.1. ) And the content of Mn is 10 ppm or less.

The present invention will be described in more detail below.

The Tb-activated rare earth tantalum-based composite oxide phosphor of the present invention can be manufactured by the method described below.

First, as the phosphor raw material, the following four types of raw materials having a total content of Nb of 50 ppm or less or a total content of Mn of 10 ppm or less obtained by sufficient purification, i) yttrium oxide (Y ₂ O ₃ ), lanthanum oxide (La
₂ O ₃ ), gadolinium oxide (Gd ₂ O ₃ ), lutetium oxide (Lu
₂ O ₃ ), and easily heated to Y ₂ O ₃ ,, La ₂ O ₃ ,, Gd ₂ O ₃ ,, Lu ₂ O
One or more kinds of compounds selected from nitrates, carbonates, chlorides, hydroxides, oxalates, and other yttrium compounds, lanthanum compounds, gadolinium compounds, and lutetium compounds, which can be changed to ₃ , ii) tantalum oxide ( Ta ₂ O ₅ ) and tantalum dioxide (TaO ₂ ), which can be converted to Ta ₂ O ₅ by heating, tantalum chloride (Ta
One or more compounds selected from tantalum compounds such as Cl ₅ ) and iii) boron oxide (B ₂ O ₃ ) and boric acid (H ₃ BO ₃ ) which can be converted to B ₂ O ₃ by heating. One or more compounds selected from boron compounds, iV) terbium oxide (Tb ₂ O ₃ ) and terbium compounds such as nitrates, chlorides, carbonates and oxalates that can be converted to Tb ₂ O ₃ by heating One or more compounds selected from the following are used. Stoichiometrically (Ln _1-X , Tb _X ) ₂ O ₃ · mTa ₂ O ₅ · nB ₂ O ₃ (where Ln, m, n, x, are the same as above) (Definition is defined) and the mixture is thoroughly mixed. The mixing may be performed dry using a ball mill, mixer mill, mortar or the like, or may be performed wet in a paste form using water, alcohol or the like as a medium. In terms of the emission intensity of the obtained phosphor, the values of m, n and x are 0.98 ≦ m ≦ 1.0, respectively.
2, 0.1 ≦ n ≦ 2.0 and 2 × 10 ⁻³ ≦ x ≦ 5 × 10 ⁻² are more preferable, and when Ln is Gd, a phosphor having particularly high brightness can be obtained.

Note that among the Tb-activated rare earth tantalum-based composite oxide phosphors of the present invention, phosphors not containing B ₂ O ₃ (wherein n = 0 in the above composition formula)
It is needless to say that the above phosphor material iii) is not used in the production of the case).

Then, the phosphor raw material mixture is filled in a heat-resistant container such as an alumina crucible or a quartz crucible and baked. Firing
It is carried out at a temperature of 900 to 1500 ° C, more preferably at a temperature of 1000 to 1300 ° C. The firing may be carried out twice or more, and in that case, first 1000 to 1200 ° C.
It is more preferable that the pre-baking is carried out at 1100 to 1300 ° C for the second and subsequent bakings. Although the firing time varies depending on the filling amount of the phosphor raw material and the firing temperature, it is generally suitable to carry out the firing for 1 hour to 72 hours. That is, generally, the higher the firing temperature, the shorter the firing time.
In the case of 1200 ° C., it takes 15 hours for firing to obtain the rare earth tantalum-based composite oxide phosphor of the present invention exhibiting a predetermined emission intensity, but in the case of firing at 1400 ° C., it takes 1 to 4 hours. .

In the production of the rare earth tantalum-based composite oxide phosphor of the present invention, similar to the production method of the rare earth tantalate phosphor disclosed in Japanese Patent Publication No. 58-22063, for example, the first or second and subsequent firings are performed. Sometimes in advance in the phosphor material
Compounds such as Li ₂ SO ₄ , LiCl, and BaCl ₂ may be mixed as a flux.

When the firing is completed in this manner, the obtained composite oxide phosphor of the present invention can be obtained by subjecting the obtained fired product to various treatment operations generally adopted in the phosphor production, such as crushing, washing, drying, and sieving. .

In this way, the content of Nb is 50 ppm or less, or M
When the content of n is 10 ppm or less, the composition is (Ln _1-X , Tb _X ) ₂
A Tb-activated rare earth tantalum-based complex oxide phosphor represented by O ₃ · mTa ₂ O ₅ · nB ₂ O ₃ can be obtained.

〔Example〕

 Next, the present invention will be described with reference to examples.

Example 1 Commercially available tantalum pentoxide (Ta ₂ O ₅ ) containing 370 ppm of Nb and 180 ppm of Mn was refined to obtain a Tb having an Nb content of 1 ppm or less.
a ₂ O ₅ was obtained. Next, cadmium oxide (Gd ₂ O ₃ ) 44.6 g, the above Ta ₂ O ₅ 54.9 g with an Nb content of 1 ppm or less and terbium oxide (Tb ₄ O ₇ ) 0.465 g each phosphor raw material were mixed in the filling, Further, as a flux, LiCl and Li ₂ SO ₄ · H ₂ O are added to each of the above phosphor raw materials at 50% by weight.
The mixture was mixed, packed in an alumina crucible, placed in an electric furnace, and fired in air at a temperature of 1250 ° C. for 7.5 hours. After firing, washed with water and the fired product, after drying, sieving, composition formula (Gd _0.99, Tb _0.01) was prepared phosphor represented by ₂ O ₃ · Ta ₂ O ₅ [I].

Next, the content of Nb purified above is 1 ppm or less Ta ₂ O
_{In place of 5} , Nb ₂ O ₅ was added thereto, and Ta ₂ O ₅ having Nb contents of 20 ppm, 35 ppm and 65 ppm, respectively, was used. ], Phosphor [III] and phosphor [IV] were manufactured.

Separately, for comparison, the content of Nb is 1 ppm or less, in place of the purified Ta ₂ O ₅ above, Nb 370ppm in this
(The same amount as Nb contained in Ta ₂ O ₅ before purification) Ta ₂ O ₅ added and a phosphor [I] except that a commercially available Ta ₂ O ₅ having an Nb content of 1,270 ppm was used. A phosphor [RI] and a phosphor [RII] were manufactured in the same manner.

The amount of Nb contained in the phosphors [I] to [IV] and the phosphors [RI] and [RII] thus obtained (each phosphor is dissolved in hydrofluoric acid and analyzed by ICP). ) And the emission luminance of each of these phosphors when irradiated with 80 kVp X-rays, the results shown in Table 1 were obtained.

Figure 1 shows N in the (Gd _0.99 , Tb _0.01 ) ₂ O ₃ · Ta ₂ O ₅ phosphor.
FIG. 3 is a graph showing the relationship between the content of b and the emission luminance when excited with 80 kVp X-rays. The vertical axis of FIG. 1 indicates that the content of Nb is 1 p
It is shown as a relative value when the emission brightness of the phosphor that is pm or less is 100.

As can be seen from Fig. 1 (Gd _0.99 , Tb _0.01 ) ₂ O ₃ · Ta ₂ O ₅
The emission brightness of the phosphor represented by the formula (1) increased as the amount of Nb contained in the phosphor decreased, and particularly when the content of Nb was about 50 ppm or less, the emission brightness increased remarkably.

Although not illustrated, composition formula _{(Ln 1-X, Tb X} ) 2 O 3 ·
Represented by mTa ₂ O ₅ · nB ₂ O ₃ , (Gd _0.99 , Tb _0.01 ) ₂ O ₃ · T
For Tb-activated rare earth tantalum-based composite oxide phosphors other than the a ₂ O ₅ phosphor, it was confirmed that there is almost the same correlation between the Nb content in the phosphor and the emission brightness. It was

Example 2 A commercially available tantalum pentoxide (Ta ₂ O ₅ ) containing 180 ppm of Mn and 370 ppm of Nb was purified to obtain a T having a Mn content of 1 ppm or less.
a ₂ O ₅ was obtained. Next, gadolinium oxide (Gd ₂ O ₃ ) 44.6g Mn content below 1ppm Ta ₂ O ₅ 54.9g boron oxide (B ₂ O ₃ ) 0.870g and terbium oxide (Tb ₄ O ₇ ) 0.465g Mix each phosphor raw material thoroughly, and further, as a flux, mix 50 wt% of each of the above phosphor raw materials with LiCl and Li ₂ SO ₄ · H ₂ O, pack in an alumina crucible, put in an electric furnace, and in the air. It was baked at a temperature of 1250 ° C. for 15 hours. After firing, the obtained fired product is washed with water, dried and sieved to obtain Tb represented by the composition formula (Gd _0.99 , Tb _0.01 ) ₂ O ₃ · Ta ₂ O ₅ · 0.1B ₂ O _3.
An activated rare earth tantalum-based composite oxide phosphor [V] was produced.

Then purified To this was added MnCl ₂ instead of the content _of Ta ₂ O ₅ of Mn is 1ppm or less, the content of Mn is respectively 2 ppm, 20
Phosphor [VI], phosphor [VII] and phosphor [VIII] were manufactured in the same manner as phosphor [V] except that ppm and 75 ppm of Ta ₂ O ₅ were used.

Separately, instead of the purified Ta ₂ O ₅ with Mn of 1 ppm or less, 180 ppm of Mn (Ta ₂ O ₅
A phosphor [R III] was produced in the same manner as the phosphor [V] except that Ta ₂ O ₅ added with Mn contained therein was added.

The amounts of Mn contained in the thus obtained glory [V] to [VIII] and phosphor [R III] (each phosphor is dissolved in hydrofluoric acid and analyzed by ICP) and When the emission brightness when each phosphor was irradiated with 80 kV p-ray was measured, the results shown in Table 2 were obtained.

Fig. 2 shows the Mn content in the (Gd _0.99 , Tb _0.01 ) ₂ O ₃ · Ta ₂ O ₅ · 0.1B ₂ O ₃ phosphor and the relative emission brightness when excited by X-rays of 80 kVp. 2 is a graph showing the relationship, and the vertical axis in FIG. 2 is shown as a relative value when the emission brightness of a phosphor having an Mn content of 1 ppm or less is 100.

As can be seen from Figure 2 _{(Gd 0.99, Tb 0.01) 2} O 3 · Ta 2 O 5
The phosphor represented by 0.1B ₂ O ₃ is M contained in the phosphor.
The emission brightness was improved as the amount of n was decreased, and particularly when the amount of Mn was about 10 ppm or less, the emission brightness was remarkably increased.

Although not illustrated, composition formula _{(Ln 1-X, Tb X} ) 2 O 3 ·
Represented by mTa ₂ O ₅ · nB ₂ O ₃ , (Gd _0.99 , Tb _0.01 ) ₂ O ₃ · T
Regarding the Tb-activated rare earth tantalum-based complex oxide phosphors other than the a ₂ O ₅ .0.1B ₂ O ₃ phosphor, the Mn content in the phosphor and the emission brightness are similar to those in FIG. It was confirmed that there is a correlation.

The intensifying screen used as the fluorescent film of the terbium-activated rare earth tantalum-based composite oxide phosphor of the present invention is particularly excellent in graininess, in addition to general X-ray photography by X-rays with a tube voltage of 50 to 150 kV, It can be used in combination with a single-sided emulsion film or a double-sided emulsion film for low-voltage X-ray photography with X-rays having a tube voltage of 20 to 40 kV (mammography etc.).

〔The invention's effect〕

As described in detail above, by removing as much as possible the amount of Nb and / or Mn contained in the Tb-activated rare earth tantalum-based composite oxide phosphor, the green emission intensity under X-ray excitation is made to be the conventional one. Since it can be remarkably improved, it is useful, for example, as an intensifying screen or an X-ray fluorescent plate used in combination with an ortho-type X-ray film.

[Brief description of drawings]

1 and 2 are Tb containing the phosphor of the present invention.
3 is a graph showing the correlation between the Nb content and the relative emission brightness and the correlation between the Mn content and the relative emission brightness in the activated rare earth tantalum-based composite oxide phosphor.

Claims (2)

[Claims] 1. A composition formula of (Ln _1-X , Tb _X ) ₂ O ₃ .mTa ₂ O ₅ .nB ₂ O ₃ (where Ln is at least 1 selected from Y, La, Gd and Lu). Is a seed element, and m, n and x are 0.95 ≦
It is a number satisfying the conditions of m ≦ 1.05, 0 ≦ n ≦ 5.0 and 5 × 10 ⁻⁴ ≦ x ≦ 0.1. ) And having a niobium (Nb) content of 50 ppm or less, a terbium-activated rare earth tantalum-based complex oxide phosphor. 2. The composition formula is (Ln _1-X , Tb _X ) ₂ O ₃ .mTa ₂ O ₅ .nB ₂ O ₃ (where Ln is at least 1 selected from Y, La, Gd and Lu). Is a seed element, and m, n and x are 0.95 ≦
It is a number satisfying the conditions of m ≦ 1.05, 0 ≦ n ≦ 5.0 and 5 × 10 ⁻⁴ ≦ x ≦ 0.1. ) And having a manganese (Mn) content of 10 ppm or less, a terbium-activated rare earth tantalum-based composite oxide phosphor.