FR2466497A1 - Luminophores for colour TV screens or other visual display appts. - esp. using zinc sulphide activated by oxysulphide contg. yttrium plus europium, terbium or thulium - Google Patents

Abstract

The deposited luminophore contains (a) a matrix based on ZnS, CdS, ZnSe, CdSe, ZnF2, and/or CdF2; plus (b) 1-6 mole.% of A(2(1-x)Ln2XO2X; where A is an atom of Y, La, or Gd; Ln is Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, or T,; X is S or Se; and x=0.1-0.7, esp. 0.2-0.5. The deposit is pref. a film 0.2-1 mu thick; and matrix(a) is pref. ZnS, whereas A is pref. Y or La; and Ln is pref. Eu, Tb or Tm, while X is sulphur. The deposit is pref. formed by sputtering in a chamber contg. a cathode coated with the luminophore and an inert gas at 0.01-0.0001 torr, which may contain up to 5% O2, so the luminophore is deposited on a substrate. The deposit is pref. annealed 1/2 h at ca. 500 deg.C. in inert gas, esp. argon. High brilliance can be obtd. on large screens for the entire spectrum of visible light.

Description

 The invention relates to luminescent deposits.

 It more particularly relates to new luminescent deposits, in particular cathodo- and especially electroluminescent, consisting of a matrix based on sulfide, selenide or fluoride of zinc or cadmium and containing "lumocen" centers, that is to say ie centers capable of providing, under excitation, for example by electron bombardment, luminescence coming from a complex center of molecular type.

 The invention also relates to a process for the preparation of such deposits and means which allow both the implementation of this process.

The invention further relates to the use of these deposits.

 Luminescent deposits are currently the subject of much research, given the multiple and varied applications that they already present or that we are considering.

 This is particularly true with regard to layered deposits having cathodoluminescent and even more electroluminescent properties. Despite the research already carried out, it is especially in the field of thin electroluminescent layers that many problems remain to be resolved. This research aims to obtain light-emitting devices in thin layers of large surface area and of sufficiently high brightness to allow applications such as, for example, obtaining three-color television screens, three-color matrix screens, for example in consoled of computers, light advertising, mono or full color display or even color or white light lighting by a solid system.

So far the problem has been solved only very partially. Indeed, flat screens have already been produced emitting, in electroluminescence, an orange color (at 5800 A) from an active layer consisting of a zinc sulfide matrix doped with Mn2 + ions.

 Other solutions have also been proposed which theoretically make it possible to obtain, according to the operating conditions, emissions covering the entire visible range of wavelengths, without however providing a satisfactory solution from the practical point of view.

We have thus proposed to introduce, in the matrix of
ZnS, complex centers called "Lumocen" (Luminescence from Molecular Centers), that is to say molecular centers enabling luminescence to be obtained. More precisely, it has been proposed to introduce, into the ZnS matrix, luminescent centers LnF3 - (Ln representing a lanthanide emitting in the visible). Thanks to the judicious choice of the lanthanide (s) used, it is thus possible to obtain luminescence for each of the visible wavelengths.

Unfortunately, the gloss levels obtained with this system are insufficient for the applications - envisaged.

The object of the invention is therefore to obtain luminescent deposits, in particular electroluminescent deposits, for the whole range of visible wavelengths and having a sufficient level of gloss for the applications indicated above.

This object was achieved thanks to the invention which relates to a luminescent deposit comprising a) a base matrix of ZnS, CdS, ZnSe, CdSe, ZnF2, CdF2
or a mixture of at least two of these compounds and b) 1 to 6% by mole / mole of matrix of an oxysulfide or
complex oxyselenide of general formula
A2 (lx) Ln2xO2X (I)
in which
A represents an atom of yttrium, lanthanum or
gadolinium;
Ln represents an atom of praseodymium, neodymium, sama
rium, europium, terbium, dysprosium, holmium, erbium
or thulium;
X represents a sulfur or selenium atom; and
x is a number between 0.1 and 0.7.

The deposit is preferably in the form of a thin layer having a thickness of 0.2 to
The matrix is preferably based on ZnS.

In the general formula I above - A preferably represents an atom of yttrium or of
lanthanum; - Ln preferably represents a europium atom,
terbium or thulium which when excited
by accelerated electrons> provide the three
fundamental colors namely red, green
and blue respectively;
X preferably represents a sulfur atom; and
x preferably has a value between 0.2 and
0.5.

 The subject of the invention is furthermore, as means which can be used for the preparation of luminescent deposits according to the invention, the oxysulphides and oxy-sulfides of general formula I as defined above which have a new composition compared to that of the compounds of same type used so far in which x has a value between 0.05 and 0.1. They can be prepared for example by coprecipitation of the oxalates of the elements A and Ln chosen, present in the proportion x, then calcination to form the oxide of formula A2 (Ix) Ln2x03 then finally calcination of this oxide in the presence of H2S or a selenide derivative as appropriate.

The invention also relates, as a raw material for the preparation of the above-mentioned deposits, to the mixtures obtained from 10) ZnS, CdS, ZnSe, CdSe, ZnF2, CdF2 or the mixtures ob
held from at least two of these compounds and 20) a complex compound of general formula I such that
defined above, in the proportion of 1 to 6% in
mole / mole of the compound or mixture of compounds according to 10).

 In accordance with the invention, the above deposits can be obtained by implementing a method belonging to the so-called sputtering technique, or radiofrequency sputtering.

This method is characterized in that inside a vacuum spray enclosure (sputte ring), in which the pressure of the residual gases is less than 10 5 torr and in which are arranged on the one hand at least a substrate to receive the luminescent deposit and on the other hand at least one cathode comprising, optionally as a mixture, to the monks one of the compounds ZnS, CdS, Zone, CdSe, ZnF2 and CdF2, and 1 to 6% expressed in mole / mole d '' a complex oxysulfide or oxyséléniure of general formula
A2 (lx) Ln2xo2 (I) in which A, Ln, X and x are defined as previously successively - a gas mixture consisting of an inert gas is introduced
you can contain up to 5% oxygen, the final pressure should be from 10 to å 10 4 torr,
and - depositing is carried out by sputtering
on the substrate of the material of which
cathodes.

During the implementation of this process, the speed of the deposit and its thickness are controlled for example according to the interference method, by means of a laser.

 Advantageously, the deposit thus obtained is subjected to an "annealing" under an inert atmosphere, preferably of argon, at a temperature in the region of 500 "C, for approximately 30 minutes, in order to increase its luminous efficiency, that is to say its shine.

According to a particularly preferred embodiment of the invention, the compound intended to constitute the matrix (that is to say ZnS, CdS, ZnSe, CdSe, ZnF2 or
CdF2 or the mixture of at least two of these compounds) and the selected oxysulfide or oxyséléniure, are pulverized starting from a cathode made up of their mixtureJdans the desired proportions and obtained starting from their powders.

According to another embodiment of the invention, the compounds constituting the luminescent deposit are sprayed from separate cathodes.

 According to yet another embodiment of the invention, the cathodes subjected to spraying comprise a layer of the compound intended to constitute the matrix, provided on its surface with small pellets of the chosen oxysulfide or oxyséléniure.

The conditions for implementing the method according to the invention, in particular the temperature of the substrate, depend largely on the various parameters involved and in particular on the characteristics of the enclosure. The optimal conditions are defined by preliminary tests.

The vacuum spraying enclosure (or "sput tering1,") essentially comprises - a radio frequency diode module of the type sold for example by the company MATHIS or CVC, but in which the cathode is in the low position ?; - a system of heating and cooling of the substrate holder, and - an optical system for checking the thickness of the deposit.

 The cathode support can be produced from a metal disc, for example aluminum. According to the particularly preferred embodiment of the invention, a mixture, in the desired proportions, of the compound or mixture of compounds intended to constitute the matrix and of the compound of general formula I chosen, for example, is deposited on this disc. intermediate of a paste prepared using an inert volatile solvent, such as acetone, with subsequent evaporation of said solvent.

 The nature of the substrate is chosen according to the envisaged applications, the existence of a possible annealing and the expansion coefficients of the deposits made.

The inert gas which is introduced into the enclosure is preferably argon.

 A certain proportion of oxygen is used when it is desired to compensate for the oxygen deficits possibly observed during preliminary tests carried out in the presence of an inert gas alone. The proportion of oxygen in the gas mixture depends on the experimental conditions, for example pumping and deposition rates.

Sputtering can be performed using a radio frequency diode system, the principle of which is well known.
Whatever the mode of implementation of the process according to the invention, the "Lumocen" complex centers are introduced into the matrix without decomposition and without forming agglomerates.

The deposits obtained, in particular when they are in the form of a thin layer, can constitute the active element in a nescent electrolum cell made up of a stack having the suc cession: "metal-i anti-semiconductor soil- anti-metal isol "or MISIM, operating under alternating voltage.

The cells obtained from the thin layers according to the invention can be supplied with alternating current (sinusoidal or pulsed) of 5 kHz, at voltages of 50 to 200 volts effective.

The light intensities emitted have values of approximately 10 to 20 times greater than those of cells "doped" with rare earth fluorides, but approximately 5 times lower than those emitted by the device with zinc sulfide "doped" by ions. manganese of the prior art. In addition, and this is an important remarkable characteristic of these new cells, no "saturation" of the light is observed when the applied voltage is high.

By combining several deposits, in particular in thin layers, comprising oxysulfides or oxyséléniures in which the elements Ln are different, it is possible to constitute devices operating, in particular in electroluminescence, in polychromy.

The following example serves to illustrate the invention, without however limiting its scope.

EXAMPLE
Realization of a thin layer of ZnS doped with Y2 (1-x) EU2xO2S
Making the cathode
80.5 g of ZnS powder of 99.95% purity and 5.9 g of powder of 2 (1-x) Eu202S (with x are mixed in acetone, using a magnetic stirrer = 0.3). a mixture is thus obtained containing 1.4% of Eu3 + per mole of ZnS.

 The mixture obtained is deposited on an aluminum support 10 cm in diameter to serve as a cathode support, then dried first in air at 1500C and then under vacuum at 500 "C. The thickness of the cathode is then 2.5 mm.

Creation of a layer.

 In an enclosure in which the cathode described above and a heat-resistant glass substrate designated by the trademark Pyrex having a surface area of 25 x 35 mm have previously been placed face to face at a distance of 4 cm. creates a molecular vacuum; Lre of 10-6 torr. A gaseous mixture consisting of argon and 1 of oxygen is then introduced into this enclosure while maintaining a secondary pumping greatly reduced by an adjustment valve, this for 30 minutes. The pressure in the enclosure then stabilizes at 4.10 3 torr.

In parallel, the substrate is heated under vacuum for one hour to 400 "C.

Cathodisue spraying
The pressure being maintained at the value of 4.10 torr under an argon atmosphere containing 1% of oxygen with continuous gas flow and pumping, sputtering is carried out by means of a radio frequency diode system at a continuous voltage of 1100 V with a power of 60 W, the height of the ion acceleration zone or "dark space" being 2.7 cm and the temperature of the substrate having been brought back to 1800C.

 The deposition speed is optically controlled using a laser; it is between 30 and 50 A per minute.

The spraying is stopped when the layer obtained has a thickness of 5000 A.

The generator used is an RD Mathis device
SG 1250, 1250 watts and 13.56 MHz.

The "sputtering" module produced in the laboratory essentially comprises the elements mentioned above.

Athermic treatment of the thin layer obtained.

In order to increase the light efficiency of the thin layer, it is subjected to annealing at 5000 ° C. for 30 minutes, under an argon atmosphere.

Results
The resulting layer is luminescent in red (approx. 6000 A).

 A cell prepared from this layer and operating at 155 V and 5 kHz has a luminance (or "brightness") of 70 cd / m2. No saturation is observed when the voltage increases.

 By proceeding in a similar manner, other thin luminescent layers can also be emitted, also emitting in the red (by using another matrix or by replacing, / in the compound of general formula I, yttrium with lanthanum or optionally gadolinium and sulfur by selenium). It is also possible, by replacing europium with another rare earth emitting in the visible, to obtain other visible colors, in particular blue and green by using terbium or thulium respectively.

In particular, thin layers emitting in one of the fundamental colors can be produced using a zinc sulfide matrix "doped" by
Y2 (1-x) EuxO2S or La2 (1-x) Eu2xO2S for red Y 2 (Ix) Tb2xO2S or La2 (lx) Tb2xo2s for green; and Y2 (Ix) Tm2xO2S or La2 (1-x) Tm2xO2S for blue.

Thus, for example, a thin layer emitting in the green, of ZnS "doped" with La2 (ix) Tb2x02S, was prepared according to the method described above. A cell obtained from this layer and operating at 151 V and 5 kHz a a luminance of 350 cd / m2. No saturation is observed when the voltage increases.

 As goes without saying and as it already follows from the above, the invention is in no way limited to those of its modes of application and embodiments which have been more especially envisaged; on the contrary, it embraces all its variants.

Claims (16)

1. Luminescent deposit comprising a) a matrix based on ZnS, CdS, ZnSe, CdSe, ZnF2,  CdF2 or a mixture of at least two of these compounds  and b) 1 to 6 mol% / mol of a complex compound of  formula A2 (Ix) Ln2xO2X (I)  in which  A represents an atom of yttrium, lanthanum or gadolinium; Ln represents an atom of praseodymium, neodymium, sama  rium, europium, terbium, dysprosium, holmium, erbium or thulium;  X represents a sulfur or selenium atom ;; and  x is a number between 0.1 and 0.7. 2. Luminescent deposit according to claim 1, characterized in that it is in the form of a thin layer having a thickness of 0.2 to I - 3. Luminescent deposit according to claim 1 or 2, characterized in that the matrix is based on ZnS. 4. Luminescent deposit according to any one of claims 1 to 3, characterized in that, in the compound of general formula I, A represents a yttrium or lanthanum atom. 5. Luminescent deposit according to any one of claims 1 to 4, characterized in that Ln represents a europium, terbium or thulium atom. 6. Luminescent deposit according to any one of claims 1 to 5, characterized in that X represents a sulfur atom. 7. Luminescent deposit according to any one of claims I to 6, characterized in that x is between 0.2 and 0.5. 8. Method for preparing the luminescent deposit according to any one of claims 1 to 7, characterized in that inside a vacuum spraying enclosure (sputtering), in which the pressure of the residual gases is. less than 10 5 torr and in which are arranged on the one hand at least one substrate to receive the luminescent deposit and on the other hand at least one cathode comprising, optionally in mixture, at least one of the compounds ZnS, CdS, ZnSe, CdSe , ZnF2 and CdF2, and 1 to 6% expressed in mole / mole of a complex oxysulfide or oxyselenide of general formula A2 (ix) 2x 2 (I) in which A, Ln, X and x are defined as previously successively - we introduce a gas mixture consisting of a gas  inert which may contain up to 5% oxygen, the final pressure must be 10- to 10-4 torr, and - the sputtering is carried out  on the substrate of the material of which cathodes. 9. The method of claim 8, characterized in that it further comprises a step of annealing under an inert atmosphere, preferably of argon, at a temperature in the region of 500 "C, for approximately 30 minutes. 10. Method according to claim 8 or 9, characterized in that the matrix and the selected oxysulfide or oxyséléniure are pulverized starting from their mixture, in the desired proportions, constituting starting from their powders; the cathode (s). 11. Method according to claim 8 or 9, characterized in that the compounds intended to constitute the luminescent deposit are sprayed from separated cathodes. 12. Method according to claim 8 or 9, characterized in that the cathode comprises a layer of the compound intended to constitute the matrix, provided on its surface with small pellets of the chosen oxysulfide or oxyséléniure. 13. Complex compound intended for the preparation of the luminescent deposit according to any one of claims 1 to 7, characterized in that it corresponds to the general formula  A2 (ix) Ln2xO2X (I) in which A represents an atom of yttrium, lanthanum or gado  linium; Ln represents an atom of praseodymium, neodymium, sama rium, europium, terbium, dysprosium, holmium, erbium  or thulium; X represents a sulfur or selenium atom; and x is a number between 0.1 and 0.7. 14. Meln9e intended for the implementation of the method according to claim 10, characterized in that it comprises powder of znS, CdS, ZnSe, CdSe, ZnF2, CdF2 or a mixture of the powders of at least two of these compounds and 1 to 6 mole / mole powder of the complex compound according to claim 13. 15. Light-emitting cell, characterized in that it comprises, as active element, at least one deposit according to any one of claims 1 to 7. 16. Use of luminescent deposits according to any one of claims 1 to 7 for the manufacture of three-color television screens, three-color matrix screens, luminous advertising panels or mono or full color display, or billboards. lighting in color or white light by a solid system.