DE2652480C2 - Alkaline earth tetraborate phosphor and its use - Google Patents

Description

The invention relates to an alkaline earth tetraborate phosphor activated with divalent europium Formula Sri _, _ pMe "Eu ^ B" O7. Further refers to the Invention to the use of such a phosphor.

The activation of alkaline earth borates with divalent europium is known. In doing so, substances are obtained when excited with ultraviolet radiation, the rather narrow-band emission of bivalent Have europium. This emission band lies either in the deep blue, depending on the existing basic grid or in the near ultraviolet part of the spectrum. In DE-OS 19 19 071, for example, that with bivalent Europium activated barium octaborate (BaBsOu) described, which has an emission band with a Has a maximum at about 400 nm. From US-PS 36 57 141 that is activated with divalent europium Strontium fluoroborate (SrB, Ot,., F) known its maximum of the emission band is around 370 nm. A disadvantage of the known Fluoroboral is that its Manufacture is difficult and can cause undesirable release of fluorine into the atmosphere. In JP-OS 74/67 892 describes a calcium-containing strontium teiraboral activated with bivalent europium, for example Sro.qCao.iB ^. This substance owns when excited by short-wave ultraviolet radiation, an effective emission with a maximum about 370 nm and a half width of about 20 nm.

Such a narrow-band emission in the wavelength range between 350 nm and 390 nm can be achieved with a large Advantage when influencing photochemical processes such as lacquer hardening, plaster hardening, photopolymerization, Xerography and the like. can be applied.

The quantum yield and the radiation yield of the well-known alkaline earth tetraborate luminescent substances however, there is still a lot to be desired.

The invention is based on the object of creating new phosphors which have an increased quantum yield and have an increased radiation yield.

This object is achieved according to the invention in that in the formula Mc at the beginning represents at least one of the elements barium and magnesium and 0 < χ <0.25 and 0.003 <ρ <0.20.

The inventive phosphor can be short-wave Ultraviolet radiation are excellently excited, for example by the radiation of a pressure mercury vapor discharge lamp (predominantly 254 nm). The emission obtained in this way is narrow-band with a maximum at approximately 368 nm and a half-width of approximately 18 nm.

The basic lattice of the phosphors according to the invention consists of strontium tetraborate, in which part of the strontium is replaced by barium and / or magnesium is. The crystal structure of strontium tetraborate (orthorhombic symmetry) is retained. Surprisingly it has been found that such a replacement increases the quantum yield and the Radiation yield compared to pure stronlium traborate In comparison to the well-known calcium-containing strontium tetraborate, there is one more

ι s obtained greater increase in radiation output. It has been found that even small amounts of barium and / or magnesium cause an increase in the radiation yield. At a value χ of the barium and / or magnesium content of, for example, 0.05

2 «a considerable increase in yield can already be achieved. When replacing large amounts of strontium by Barium and / or magnesium, in turn, leads to a decrease in the radiation output. A substitution of more than 25 mole percent of the strontium (x> 0.25)

2 ^r > therefore not applied

The europium content ρ can be between those given above wide limits can be chosen. For values of p <0.003, the radiation yields obtained in practice are too low and for values of ρ above 0.20, the

to Sirahlungsausbcutc by concentration deletion small amount.

A particular advantage of the luminescent borates according to the invention is that they are quite coarse-grained Powders are available. This applies in particular to the magnesium-substituted borates according to the invention, whose mean grain diameter (determined with the Fisher Sub Sieve Sizer) is approximately 5.0 μm. A Such a powder can be applied much more easily in a fluorescent screen than the known, in an analogous manner produced potassium / .ium hally strontium tetraborate (approx 1V2 (im) and the well-known pure strontium telraborate (about 33 µm). Furthermore, the luminous properties of such a coarse-grained powder remain the same Better get mounting in umbrellas.

4 ^r > The highest radiation yields are obtained with borates according to the formula given, where 0.05 <x < 0.20 and 0.01 <p <0.05. These values of χ and ρ are therefore preferred.
The phosphor according to the invention is preferably used in pressure mercury vapor discharge lamps, since the luminescent borates are excited by the 254 nm radiation of such lamps.

The invention is described below with reference to her

positional examples and measurements as well as a drawing

v-, explained in more detail.

In the drawing shows

F i g. 1 schcinatically a low pressure mercury vapor discharge lamp and

F i g. 2 in a diagram the spectral energy consumption

bo division of the radiation emitted by phosphors.

F i g. 1 shows a low pressure mercury vapor discharge pulse with a piston 1. At the ends of the Lamp are arranged electrodes 2 and 3, / between which the discharge is maintained. The interior

h ^r i ropes of the plunger 1 is covered with a luminescent layer 4, which contains a lumincszierendes borate according to the invention. This luminous layer can be applied to the bulb t in a manner known per se.

Preparation example I
You are suspended

0.88 moles of SrCO ₃
O ₁ IOMoI BaCO ₃
0.01 mol Eu ₂ O ₃ and
4.00 MoI H ₃ BO ₃

in 1 liter of water at 70 ^° C. HNO _{3 is} added to this suspension so that a solution is obtained. About 2 liters of a mixture (1: 1 parts by volume) of NH «OH and a polar organic solvent, for example acetone, are carefully added to this solution, whereby a mixed hydroxide is precipitated. The precipitate is then filtered off and dried. It is then subjected to heating for 2 hours at COO ⁰ C in air. The product obtained in this way, after cooling and comminution, is heated again, specifically for 3W ₂ hours at 920 ^° C. in a nitrogen stream which contains 0.75% by volume of hydrogen. After cooling and grinding, the phosphor, which _{corresponds to the formula Sr 0} , gsBao.ioEuo.o2B407, is ready for use. The spectral energy distribution of this substance when excited with short-wave ultraviolet radiation (mainly 254 nm) is shown in Fig. 2 (curve 1). In Fig. 2, the wavelength X (in nm) is on the horizontal axis and the radiation energy £ (in arbitrary units) plotted on the vertical axis. It can be seen that the borate according to the invention has its emission maximum at 368.5 nm and a half-value width of 17.9 nm. For comparison purposes, the spectral energy distribution of the known lead-activated barium disilicate is shown in FIG .

Production example II

Here the process is carried out as in Example I ₁ , however, 0.93 mol of SrCO ₃ and 0.05 mol of Ba-CO _{3 are used} instead of the amounts mentioned in Example 1. The obtained phosphor has the formula

the same formula as the substance of Example I. The mean grain diameter of the powder is 4.2 μm.

Preparation example V Again, Example I is repeated, but with

the first heating at 900 ° C takes place The generated

Phosphor of the formula given in Example 1

corresponds to, has an average grain diameter of

ίο 6.7 μπι.

Preparation example VI

A substance with the formula as in Example I, namely Sr ₀ JItIBaOJaEu (MuB ₄ O _7. Can also be obtained by carefully mixing

0.88 moles of SrCO ₃

O ₁ IOMoI BaCO ₃

2 «0.01 mol Eu ₂ Oj

4.00 MoI H ₃ BO ₃

can be obtained in a ball mill. Thereafter, the mixture is heated in an open crucible for 2 hours at 850 ° C in air After cooling, the obtained product is crushed and then 3V ₂ hours at 920 ⁰ C in a nitrogen atmosphere containing 0.75 vol .-% hydrogen, heated again. After cooling and crushing it is luminescent

Borate ready to use.

The results of measurements on the substances obtained in accordance with the preparation examples described above are summarized in the table below. In the table, for each example, in addition to the formula of the phosphor in the LO column, the ultraviolet radiation yield in% in relation to the radiation yield of the known lead-activated barium disilicate and in column d ", the mean grain diameter in μm. For the sake of comparison, measurements on the known strontium tetraborate, the known calcium-containing strontium tetraborate and the known strontium fluoroborate are included as examples a, b, c. These known substances are prepared in the same manner as described in Preparation Example I.

45

Example funnel

LO%

Preparation example III a

50 b

Example I is repeated, with 0.05 mol of c MgCO ₃ · Mg (OH) ₂ · 3 H ₂ O II

instead of BaCO _{3 is} used. The substance 55 IV produced in this way corresponds to formula V.

208 3.3 184 1.5 168 2.2 226 3.4 224 - 218 5.0 229 4.2 224 6.7 224 4.7

The spectral energy distribution of this substance is shown in FIG. 2 shown as curve 2

1 sheet of drawings Preparation example IV

Example I is repeated in the sense that the first heating of 2 hours in air now takes place at a temperature of 850 ⁰ C. The product produced owns

Claims (3)

Patent claims: 1. Alkaline earth tetraborate phosphor activated with divalent europium the formula characterized in that Me represents at least one of the elements barium and magnesium and 0 < χ £ 0.25 and 0.003 <ρ <0.20. 2. Luminous substance according to claim 1, characterized in that that £ 0.05 * <0.20 and 0.01 <ρ <0.05. 3. Use of the phosphor according to claim 1 or 2 in the luminescent screen of a low-pressure mercury vapor discharge lampc.