JPS5933157B2 - luminous screen - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a luminescent screen having a luminescent alkaline earth metal borate activated with divalent europium.

Furthermore, the invention relates to a low-pressure mercury vapor discharge lamp equipped with such a luminescent screen, as well as to the luminescent borates described above. It is known to activate alkaline earth metal borates with divalent europium.

In this way, a material is obtained which exhibits a relatively narrow band emission of divalent europium when excited with ultraviolet radiation. This emission band is determined by the host lattice used.
ce) in the deep blue or near ultraviolet part of the spectrum, depending on the
For example, Dutch Patent Application No. 6,806,648 discloses that barium octaborate (Ba
B8013). U.S. Patent No. 36571
No. 41 discloses strontium fluoroborate (SrB4O6.5F) which is activated with divalent europium and has an emission band having a maximum value at about 370 nm. This known fluoroborate is difficult to produce and has the disadvantage that undesirable emissions of fluorine into the atmosphere can occur. In the patent application No. 1978-67892, sr0.9ca0.1B4o
Calcium-containing strontium tetraborate activated with divalent europium, such as No. 7, has been demonstrated. When excited with short-wavelength ultraviolet radiation, this material has a wavelength of about 370 nm.
It shows an effective emission with a maximum value of , and a half-width of about 20 nm. Such a narrow band of wavelengths in the wavelength range of 350-390 nm can be used very advantageously for the operation of photochemical treatments such as lacquer curing, plaster curing, photopolymerization, xerography, etc.

An object of the present invention is to provide a novel luminescent material that can be used for such purposes. The luminescent screen of the present invention has a luminescent alkaline earth metal borate activated with divalent europium, the borate having the following formula (wherein Me represents at least one element of barium and magnesium,
O<x×0.25, 0.003×p×0.20)
It is characterized by satisfying the following.

The luminescent alkaline earth metal borates of the luminescent screen according to the invention can be excited very well by short wavelength ultraviolet radiation, for example the radiation of a low-pressure mercury vapor discharge lamp (principally 254 nm).

The luminescence thus obtained is a narrow band luminescence having a maximum value at about 368 nm and a half width of about 18 nm. The host lattice of the luminescent material according to the invention consists of strontium tetraborate, with some of the strontium being replaced by barium and/or magnesium.

The crystal structure of strontium tetraborate (orthorhombic symmetry) is maintained. Surprisingly, it has been found that such substitution results in an increase in quantum efficiency and radiation output compared to pure strontium tetraborate. Even with the known calcium-containing strontium tetraborate, even greater gains in radiation output are obtained. It has been determined that small amounts of barium and/or magnesium cause an increase in radiation output. For example, significant gains can be obtained with a value of barium and/or magnesium fraction x equal to 0.05. If large amounts of strontium are replaced by barium and/or magnesium, the radiation output is reduced again. Therefore, no more than 25 mol % of strontium is substituted (x0.25). The europium fraction p can be selected between the wide limits mentioned above. For values of p below 0.003, radiation outputs are significantly lower for practical applications, and for values of p greater than 0.20, radiation outputs are extremely low due to concentrated quenching.

A particular advantage of the luminescent borates according to the invention is that they can be obtained as relatively coarse-grained powders.

This is particularly true for the magnesium substituted borates according to the invention, whose average particle size (as measured by Fisher Sub Sieve Sizer) is approximately 5.0 microns. Such powders are more easily applied to luminescent screens than the known calcium-containing strontium tetraborate (approximately 1.5 μ) and the known pure strontium tetraborate (approximately 3.3 μ) obtained in a similar manner. Furthermore, the luminescent properties of such coarse-grained powders are better preserved when they are applied to screens. The highest radiation efficiency is 0.05<.
It can be obtained by using a borate that satisfies x x 0.20 and 0.01 x p < 0.05.

Therefore, these values of X and p are preferable. Preferably, the luminescent screen of the invention is used in a low pressure mercury vapor discharge lamp.

The reason is that the 254nm of discharge lamps that emit borates
This is because it is optimally excited by radiation. The invention will now be explained with reference to the drawings and examples.

The low-pressure mercury vapor discharge lamp shown in FIG.

Electrodes 2 and 3 are placed at both ends of the discharge lamp to maintain a discharge between them. The inside of the envelope 1 is coated with a luminescent layer 4 containing a luminescent borate according to the invention. This luminescent layer can be applied to the envelope 1 by conventional methods. Example 1 0.88 mol SrcO3 and 0.10 mol BacO
3, 0.01 mol of EU2O3, and 4,00 mol of H
3BO3 was suspended in water 11 at 70°C.

HNO3 was added to the resulting suspension to form a solution. N.H.
A mixture of 4OH and a polar organic solvent such as acetone (1:
1 volume part) approx. 2. e was carefully added to the resulting solution to precipitate the mixed hydroxide. After that, the precipitate was separated,
Dry. Next, this was heated in the air at β00° C. for 2 hours. The product thus obtained is cooled, ground and again reduced to 0.
3.5 at 920°C in a nitrogen stream containing 75% hydrogen by volume
heated for an hour. After cooling and grinding, the formula SrO. 88BaO. l
OEUO. . A luminescent material satisfying 2B4O7 was obtained in a usable state.

Short wavelength ultraviolet radiation (primarily 254 nm) of such materials
The spectral energy distribution due to excitation at is shown in Figure 2 (curve 1). In FIG. 2, the wavelength λ (Nm) is plotted on the horizontal axis and the radiant energy E (arbitrary unit) is plotted on the vertical axis. It is clear that the borate according to the invention has an emission maximum at 368.5 nm and a half width of 17.9 nm. For comparison, Figure 2 shows the spectral energy distribution of the known lead-activated barium disilicate, a luminescent material often used to date in low-pressure mercury vapor discharge lamps to generate radiation in the ultraviolet part of the spectrum. Shown in a). Example 2 The process of Example 1 was repeated.

However, 0.93 moles of SrcO3 and 0.05 moles of BacO3 were used in place of the amounts specified in Example 1. The resulting luminescent material has the formula SrO. 93BaO. O5EuO. O2
It had B4O7. Example 3 The procedure of Example 1 was repeated.

However, instead of BacO3, 0.05 mol MgCO3
-Mg(0H)2.3H20 was used. The luminescent material thus obtained has the formula SrO. 88MgO. lOEuO. O2B
It had 4O7.

The spectral energy distribution of the material is shown in FIG. 2 by curve 2. Example 4 The process of Example 1 was repeated.

However, the initial heating in the atmosphere for 2 hours was carried out at a temperature of 850°C. The product thus obtained had the same formula as the luminescent material of Example 1. The average particle size of the powder was 4.2μ. Example 5 The process of Example 1 was repeated.

However, the first heat treatment was performed at 900°C. The luminescent material thus obtained satisfied the formula shown in Example 1 and had an average particle size of 6.7μ. Example 6 The formula shown in Example 1, ie SrO. 88BaO. lOEUO. .

A luminescent material having 2B4O7 was mixed with 0.88 mol of Src
It can also be prepared by carefully mixing 9 O3, 0.10 mole BacO3, 0.01 mole EU2O3, and 4.00 mole H3BO3 in a ball mill.

The above mixture was heated in an open crucible at 850° C. for 2 hours in air.

After cooling, the resulting product was ground and heated again for 3.5 hours at 920° C. under a nitrogen atmosphere containing 0.75% by volume of hydrogen. After cooling and grinding, the luminescent pentaborate was obtained in a usable state. The measurement results of the luminescent materials obtained in the above examples are summarized in the table below.

For each example, in addition to the formula of the luminescent material, the LO column shows the ultraviolet radiation output (%) relative to the known radiation output of lead-activated barium disilicate, and the Dm column O shows the average particle size (μm). For comparison, the measured values for known strontium tetraborate, calcium-containing strontium tetraborate, and strontium fluoroborate are shown in Example A. b
and c. These known materials were prepared in the same manner as described in Example 1 and 5.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of an example of a low-pressure mercury vapor discharge lamp according to the present invention, and FIG. 2 is a curve diagram showing the spectral energy distribution of luminescent radiation of two types of luminescent borates of the present invention. It is. 1... Envelope, 2, 3... Electrode,
4...Light-emitting layer.

Claims (1)

[Claims] 1. In a luminescent screen for use in a low-pressure mercury vapor discharge lamp having a luminescent alkaline earth metal borate activated with divalent europium, the borate has the following formula Sr_1_-
_x_-_pMe_xEu_pB_4O_7 (M in the formula
e represents at least one element of barium and magnesium, 0<x≦0.25, 0.003≦p≦0.20
A luminescent screen characterized by satisfying the following. Quadratic formula Sr_1_-_x_-_pMe_xEu_pB_4O_
7 (Me in the formula represents at least one element of barium and magnesium, 0<x≦0.25, 0.003≦
A luminescent alkaline earth metal borate activated with divalent europium satisfying p≦0.20.