FR2464983A1 - Forming layer of luminescent oxy:sulphide - by sputtering in presence of sulphide, then heat treating - Google Patents

Abstract

Method for forming a base layer of phosphor of formula (T(1-x)Lnx)2O2S (where T is one or more of La, Gd, Y and Lu; Ln is one or more of Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb and Pm in a tervalent state, x is 0.001-0.05) by HF cathode sputtering is described in which, the sputtering is effected in a rarified atmos of inert gas. Specifically, a target comprising (T(1-x)Lnx)202S is used and a sulphide of La, Gd, Y or Lu is present in an amt. such that the oxysulphide obtd. has a S content corresp. stoichiometrically to that in this formula. The sputtering is effected in an inert gas with additional H2 at a partial pressure of 0.1-200 microns of Hg. The deposit thus obtd. is heat treated at 400-500 deg.C then subsequently in an inert atmos. or a mixt. of inert gas and hydrogen, at 500-600 deg.C. A judicious choice of colour producing oxysulphides of the above formula can produce a satisfactory energy yield of 10-15% for the 3 fundamental colours, i.e. sufficient for uses in TV screens, luminous tubes etc.

Description

 The invention relates to luminescent products, namely phosphors having matrices based on rare earth or yttrium oxysulfides and more particularly for a new process for the preparation, by high frequency sputtering, of luminescent layers. of activated rare earth or yttrium oxysulphides, as well as the means allowing the implementation of such a process.

It is known that yttrium oxysulfides and optically non-absorbing rare earths in the visible lanthanum, gadolinium and lutetium (all elements which are represented below by the symbol T) constitute excellent matrices for the preparation of phosphors activated by other lanthanides with an incomplete 4f electronic layer, namely praseodymium, neodymium, samarium, europium, terbium, dysprosium, holmium, erbium, thulium and ytterbium (and possibly promethium which is created artificially by fission of uranium}
These elements are represented below by the symbol Ln.

These phosphors which can be represented indifferently by one of the formulas (Tl, xLnx) 202S or T202S: Ln owe their luminescent properties to the radiative transitions occurring between "discrete" energy levels of the configuration (4f) n of l activator ion Ln3 +.

such phosphorus can be excited by photons (photoluminescence), electrons - (cathodo- and electroluminescence) or X-rays ouy
The color obtained by excitation depends on the activator Ln3 +: for example, blue is obtained with thulium Tm3 +, green with terbium Tb3 + and red with europium Eu
These phosphors have many advantages over those known previously. These advantages are in particular due to their matrix. Indeed, the oxysulfides are very stable compounds, insensitive to humidity and which oxidize in the air only above 600-700 "C; they are moreover very refractory (congruent fusion above 2000 C ).

Given these various advantages, numerous applications of these phosphors such as the manufacture of luminescent materials. For lighting, cathode ray tubes, display screens, image amplifier tubes, X-ray screens, television screens, etc. have already been considered.

 Currently used yttrium oxysulfide activated with europium (Y202S: Eu) as red phosphorus for color television screens. It is generally associated, in order to obtain the other two fundamental colors (blue and green) with conventional phosphors such as the sulfides of the (Zn, Cd) S type which have, in cathodoluminescence, higher energy yields than those of the oxysulfides. However, the zinc sulfide matrix has many disadvantages such as unreliability and poor behavior under high energy excitation. In addition, in these conventional screens the phosphors are deposited in the form of powders. Such particle coatings have many limitations, particularly with regard to the regulation of contrast.

 Now we know that thanks to a judicious choice of the elements T and Ln and their proportions the energy efficiency of mixed oxysulfides (T1 xLnx) 202S can reach a value of around 10 to 15%, especially for the three colors. fundamental, which is satisfactory for the intended applications.

We therefore thought we could remedy all of the drawbacks set out above by using, in particular for the manufacture of television screens, phosphors consisting of mixed oxysulfides as defined above, in the form of layers deposited by spraying. high frequency or "sputtering". However, the development of such structures is delicate and for this reason, this technique has not yet developed.

 Thus Maple and Buchanan (J. Vac. Sci. Technol. Vol 10, no. 5, Sept, Oct 1973) having found that a high frequency sputtering, in a rarefied commercial argon atmosphere, of a target of oxysulfide La2O2S activated with europium leads to the production of sulfur-deficient layers (part of the oxysulfide being replaced by oxide) propose, to restore the stoichiometry of the oxysulfide, to perform such sprays within argon + H2S mixtures, with very precise concentrations of these two gases, then subject the layers of oxysulfide obtained to a heat treatment at high temperature (lo000C) in a mixture of sulfur dioxide and hydrogen to restore sufficient luminescence to the phosphors.

Because of the need to respect critical concentrations of argon and hydrogen sulfide, the difficulty of controlling the structure of the deposits obtained and the low reproducibility of the results, such a process is difficult to implement industrially.

 In addition, the use of hydrogen sulfide presents hazards and inconvenience to personnel, while it is corrosive to the spraying installation.

 It has now been found that, surprisingly and unexpectedly, it is possible to prepare luminescent layers of oxysulfides by high frequency sputtering, of unocysulfide activated in the presence of a sulfide.

whereby it is no longer necessary to have a strictly determined atmosphere and which makes it possible to properly control the structure of the luminescent layers obtained, with good reproducibility of the results, while avoiding the drawbacks inherent in the use of hydrogen sulfide.

The subject of the invention is therefore a process for producing a base layer of a phosphorus corresponding to the formula (T1 xLnx) 2 2S (I) in which - T represents one or more selected trivalent metals
in the group consisting of lanthanum, gadolinium,
yttrium and lutetium, - Ln represents one or more activating trivalent metals
teurs chosen from the group made up of praseo
dyme, neodymium, samarium, europium, terbium,
dysprosium, holmium, erbium, thulium and yt
terbium (and possibly also promethium) and - x has a twist value of 1t 3 to
by high frequency sputtering of said phos
phore on a support, according to the technique called "sput
tering ", in a rarefied atmosphere including a gas
inert, characterized - a) in that a target consisting of a
mixture of oxysulfide (T1 xLnx) 202S and a sulfide
chosen in the grouy constituted by lanthanum, the
gadolinium, yttrium and lutetium, present in one
amount such that the layer of oxysulfide obtained has
a sulfur concentration corresponding to stoe
chiometry (T4xLnx) 2O2S, this spraying being
implementation in an atmosphere consisting of
inert gas with hydrogen added, under pressure
partial from 0.1 to 200 microns of mercury and - b) in that the deposit thus obtained is subjected to re
cooked, either simultaneously with spraying, by
heating the substrate to a temperature of 4CO to 5000C,
either subsequently, in an inert atmosphere or in a
medium consisting of an inert gas and hydrogen,
at a temperature of 500 to 6000C.

A device of the type described in the article by Maple can be used for spraying.
Buchanan supra. Such a device is equipped with a pumping system of the ultrahigh vacuum type (for example a turbomolecular pump associated with a titanium sublimation pump with cryogenic trap) making it possible to obtain an initial residual view of 10 to 10 8 torr. It is indeed necessary to obtain a high initial vacuum because the sulfur deficit observed during deposition is associated with the presence of oxygen in the enclosure; it was observed that when the initial vacuum is less high, it is necessary, so that the stoichiometry of the deposit is respected, to increase the proportion of sulfide.

The activated oxysulfide can be prepared according to any method known per se for the preparation of such compounds, in particular according to the method for preparing the oxysulfides of S. Larach and RE Shrader CAnalytica Chimica
Acta, 63 (1973) pages -459-463).

 It is appropriate that the proportion x of the activating element is of the order of lo 3 to 5. 10 2 because, for higher concentrations, saturation and extinction effects are observed ("Quenching").

 Although it is not imperative, it is preferable that the sulfide mixed with the oxysulfide is derived from the element T entering into the composition of the matrix of the oxysulfide used.

 The proportion of sulphide must be such that the layer of oxysulphide obtained has a sulfur concentration corresponding to the stoichiometry of the oxysulphide (Ti, x x Lynx) 2025 This concentration depends on the activator used and on the experimental conditions.

 In practice, the ideal proportion of sulphide is determined, for given working conditions, by means of the fluorescence spectra obtained by cathodic excitation of the deposited phosphors. To do this, the proportion of sulphide is gradually increased until the line due to the oxide disappears from the fluorescence spectrum. The intensity of the fluorescence due to the oxide decreases in a substantially linear manner as a function of the sulphide concentration.

 As a general rule, under the working conditions defined above, 5 to 8% of sulphide should be used, calculated on the basis of the weight of the oxy-sulphide.

The inert gas used, both in the spray enclosure and for annealing, is preferably argon.

The gas mixture used, in particular argon + hydrogen, should preferably have a high purity (N50).

In such a mixture, the hydrogen is preferably present in a proportion of 5 to 10% by volume.

The deposition can be carried out on the various usual substrates such as quartz. In addition, given the fact that the annealing is carried out at temperatures at most of the order of 600 ° C., it is possible to use as substrate glasses of the type of those marketed under the registered trademarks Pyrex or VycorX while according to the previous Maple and Buchanan method, such glasses cannot be used due to the annealing temperature of the order of 10000C applied.

 It is possible, according to the invention, to make "multilayer" deposits in order to obtain a polychromy.

 To do this, a layer of each of the phosphors emitting one of the fundamental colors desired is successively deposited on a support under the conditions defined above.

 In particular, with a view to producing color television screens, three layers of oxysulfides activated respectively by thulium, terbium and europium are deposited successively, which will provide the three basic colors, namely blue, green and red. The order in which these layers are deposited is indifferent.

 To carry out such "multilayer" deposits, it is preferable to use the same matrix, that is to say that all the oxysulfide matrices are formed from the same element T. The fact of using the same matrix allows to avoid the disadvantages of multiple layers of different chemical compounds which are often "poisoned" by interaction.

 For the production of color television screens, it will often be advantageous to use a common matrix consisting of lanthanum oxysulfide because, while for the preparation of the red phosphors all the matrices provided according to the invention are perfectly suitable, in the case of the preparation of blue phosphorus the results are clearly better when using a lanthanum oxysulfide matrix.

Annealing can be carried out under the various conditions indicated above.

 In practice, it is advantageous to successively deposit the different layers on the same support and then only to anneal under the conditions indicated above.

A further subject of the invention is a means for carrying out the process described above, which means consists of the mixture of an oxysulfide of formula
(T ixLnx) 2025 (I) in which - T represents one or more selected trivalent metals
in the group consisting of lanthanum, gadolinium,
yttrium and lutetium, - Ln represents one or more activating trivalent metals
teurs chosen from the group consisting of praseodymium,
neodymium, samarium, europium, terbium, dys
prosium, holmium, erbium, thulium and ytterbium
(and possibly also promethium) and - x has a value of the order of 10 3 to 5.10 2, and a sulphide chosen from the group consisting of lanthanum, gadolinium, yttrium and lutetium, present in a proportion of 5 to 8% relative to the weight of the oxysulfide.

 The single appended figure represents the fluorescence spectra of the red phosphors Y202S: Eu obtained for different concentrations c of Y2S3 in the sprayed mixture.

This figure shows the progressive elimination of the oxide formed as c increases.

The invention will be better understood using the nonlimiting examples which follow.

Example 1
Preparation of a thin layer of Y2O2S activated by 3.6% (in moles) of europium (red phosphorus).

The activated oxysulfide is prepared according to the method of
S. LARACH and RE SHRADER tAnalytica Chimica Acta, 63 (1973) p 459-463 j.

10 g of Y203 and 0.595 g of Eu203 are dissolved in 11 cm of pure HNO3. It is precipitated with ammonium oxalate, dried and calcined in air at 900 ° C. for 4 hours. 5 g of sulfur, 3.5 g of sodium carbonate and 1.75 g of potassium phosphate are then added; mixed with mortar and calcined for two hours at 1100OC under argon. It is then washed thoroughly and dried.

Then mixed with 0.728 g of Y2S3 to constitute the target.

The deposition is carried out on a quartz or sapphire substrate having a surface of 5/5 cm by high frequency sputtering, in a vacuum enclosure. In this enclosure, an initial vacuum of 10 a to 10 8 torr is produced, then the mixture A + H2 (5 to 20 of H2) is introduced therein under a partial pressure of the order of 6 microns of mercury.

The power used for spraying is 2 to 3 watts per cm2. A thin layer of oxysulfide is thus deposited.

This layer is calcined at 500-600 C for 5 hours under an argon atmosphere.

 According to an alternative embodiment, it is also possible to carry out the deposition on a substrate (for example glass sold under the trademark Pyrex or silica) maintained at a temperature of 400-500 "C throughout the spraying; it is in this case unnecessary to carry out a subsequent annealing.

Example 2
Preparation of a thin layer of activated GdSOS nar 3 6 (in moles) of europium (red phosphorus).

 The oxysulfide is prepared as in Example 1 from 10 g of Gd203 and 0.370g of Eu203 then this oxysulfide is mixed with 0.680 g of Gd2S3 and the mixture is sprayed under the same conditions as in Example 1 .

Example 3
Preparation of a thin layer of La202 S activated by 3.6 X (in moles) of europium (red phosphorus).

The procedure is as in the previous examples from 10 g of La203, 0.412g of Eu203 and 0.689 g of La2S3.

Example 4
Preparation of a thin layer of LaO S activated by 1% (in moles) of thullium (blue phosphorus)
For activators. Other than europium, it is possible, to obtain the oxysulfide, to directly calcine the coprecipitated oxides, in the hydrogen sulfide.

Lo g of La203 and 0.125 g of Tm203 are dissolved in 11 cm3 of HNO3. It is precipitated with ammonium oxalate and the precipitate is calcined at 9000C, in air, for 4 hours. It is then calcined at 8500C in H2S for one hour, then 0.689 g of La2S3 is added and the deposition is carried out as described in Example 1.

It is then annealed at 500 ° C. in argon. The layer obtained is strongly cathodoluminescent.

Example 5
Preparation of a thin layer of La2O2S activated by 1% (in moles) of terbium (green phosphorus).

the procedure is as in Example 4 from 10 g of La203, 0.121 g of Tb407 and 0.689 g of La2S3.

Example 6
Preparation of a thin layer of Gd202S activated by 1% (in moles) of terbium (green phosphorus).

The procedure is as in Example 4 from 10 g of
Gd203, 0.109 g of Tb407 and 0.670 g of Gd2S3 by performing the calcination of the oxides at 1100 "C in H2S and by annealing at 5500C in the argon + H2 mixture.

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

Claims (9)

1. Method for producing a phosphorus-based layer corresponding to the formula (T1 xLnx) 2 2S (I) in which - T represents one or more selected trivalent metals  in the group consisting of lanthanum, gadolinium, yttrium and lutetium, - Ln represents one or more activative trivalent metals  teurs chosen from the group made up of praseo  dyne, neodymium, samarium, europium, terbium,  dysprosium, holmium, erbium, thulium and yt-  terbium (and possibly also promethium) and - x has a value of the order of 10-3 to 5.10-, by high frequency sputtering of said phos phore on a support, according to the technique called "sput- tering ", in a rarefied atmosphere including a gas inert, characterized - a) in that one uses a target consisting of a mixture of oxysulture (Ti-x Lnx) 2O2S and a sulfide chosen from the lanthanum group, the  gadolinium, yttrium and lutetium, present in one  amount such that the layer of oxysulfide obtained has a sulfur concentration corresponding to stoe chiometry (Tix Lnx> 202S, this spraying being  implementation in an atmosphere consisting of inert gas with hydrogen added, under pressure partial deo, l to 200 microns of mercury and - b) in that the deposit thus obtained is subjected to a annealing, either simultaneously with spraying, by heating the substrate to a temperature of 400 to 500 C, either subsequently, in an inert atmosphere or in an environment consisting of an inert gas and  hydrogen, at a temperature of 500 to 6000C. 2. Method according to claim I, characterized in  what sulfide mixed with oxysulfide is derived from the element T entering into the composition of the matrix of the oxysulfide used. 3. Method according to claim 1 or 2, characterized in that the inert gas used for spraying and the annealing consists of argon. 4. Method according to any one of claims. is 5 to 8% relative to the weight of the oxysulfide.  1 to 4, characterized in that the proportion of the sulfide  spraying and possibly annealing 5. Method according to any one of the claims  represents 5 to Zo% of the total volume of gas used during  1 to 3, characterized in that the proportion of hydrogen 6. Process for the preparation of a multilayer deposit.  indicated in claim 1. annuities, to an annealing under the conditions  or all at once, following these diffe  - b) to proceed simultaneously to the various deposits and  one of the fundamental colors  5, a layer of each of the phosphors emits  methods according to one of claims 1 to conditions for implementing any  - a) to be deposited successively on a support, in the polychrome characterized in that it consists 7. Method according to claim 6, characterized in what the pulverized phosphors are made up of by shot from the same matrix. 8. Luminescent materials, in particular for lighting, cathode ray tubes, display screens, image amplifier tubes, X-ray screens, television screens, characterized in that they are provided with phosphors, present in the form of single or multiple layers, deposited by implementing the method according to any one of claims 1 to 7. 9. kernel for ia implementation of the method according to any one of claims 1 to 7, characterized in that it is constituted from the mixture of an oxysulfide of formula (T1 xLnx) 2 2S (i) in which - T represents one or more selected trivalent metals  in the group consisting of lanthanum, gadolinium,  yttrium and lutetium, - Ln represents one or more activative trivalent metals teurs chosen from the group consisting of praseodymium,  neodymium, samarium, europium, terbium1  dysprosium, holmium, erbium, thulium and ytter  bium (and possibly also promethium) and - x has a value of the order of 10-3 to 5.10-2, and a sulphide chosen from the group consisting of lanthanum, gadolinium, yttrium and lutetium, present in a proportion of 5 to 8% relative to the weight of the oxysulfide.