GB1561530A - Photoluminescent materials - Google Patents

Description

(54) IMPROVEMENTS RELATING TO PHOTOLUMINESCENT MATERIALS (71) We, BUREAU DE RECHERCHE POUR L'INNOVATION ET LA CONVERGENCE B.R.I.C.), a French Body Corporate, of 33 Quai Gallieni, 92153 Suresnes, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment This invention relates to improvements in building materials, flooring, ground covering and textile materials and, more particularly, to such products which are photoluminescent throughout.

In French Patent No. 72.01865 and its first addition No. 72.43104 and in French Patent No. 72.10248 and its first addition No.72 A3105, all in the name of the present applicants, there are described products in which in addition to the essentially conventional ingredients which enable a product to perform its basic function, i.e. which enable it to be, inter alia, useful as a true building material or a true textile material, there are incorporated throughout the mass of such products chemical matrices comprising: 1. A synthetic binder which is transparent from the near ultra-violet to the infra-red and which has a high coefficient of light transmission, examples being the acrylic, methacrylic and silicone resins.

2. Transparent fillers which have a high light transmission throughout the same spectral range, and 3. Known phosphorescent substances such as zinc sulphide, cadmium sulphide, strontium sulphide and calcium sulphide (in the case of zinc sulphide for example, light absorption takes place between 3800 and 4500 A and persistent emission occurs between 4500 and 5200 A).

In the present specification and the accompanying claims the term "phosphorescent" denotes a photoluminescence phenomenon which is of long persistence (equal to or greater than 10-8 sec.). Similary, the term "fluorescence" denotes a photo-luminescence phenomenon of short duration (less than 10- sec.); photoluminescence is a phenomenon which embraces both phosphorescence and fluorescence.

It is apparent from the above patents and additions, that it has already been found useful to increase the energy effectively utilised by such materials by making use of the light sensitivity of zinc sulphide, for example, by admixing it with aromatic substances of the polycyclic hydrocarbon type such as anthracene. In this case, the function of the anthracene or equivalent substance containing cyclic aromatic muclei is to increase the supply of incident energy within the range utilised by the materials in question so as to augment the output of the resultant persistent energy.

There is in fact a proportional relationship between the amount of energy emitted and the amount of utilisable incident energy (E = h7).

The said patents and additions describe products which are photoluminescent throughout and from which the output of useful persistent energy is increased by the presence of the cyclic nuclei-containing substances, which latter may be considered as ultra violet light absorbing substances.

The object of the present invention is further to improve such products, chiefly with respect to emission in the longer wavelengths of the visible spectrum, but also with respect to the shorter wavelengths, by including one or more fluorescent materials therein.

The present invention provides materials which are photoluminescent throughout, of the kind which include a synthetic binder which is transparent from the near ultraviolet to the infrared and which has a high coefficient of light transmission, and at least one phosphorescent substance, in which there is also present one or more substances which absorb light energy in the ultra violet region and emit light energy within the absorption spectrum of the, or one of the, phosphorescent substances prew sent, as well as one or more fluorescent substances.

Depending upon the kind of fluorescent substance which is used it may be possible to utilize the energy emitted by zinc sulphide or other equivalent substances to excite the fluorescent materials and to cause the wavelength of the persistent colour emitted by the zinc sulphides or other equivalent substances to be shifted towards the longer wavelengths of the visible spectrum. Moreover, it is possible to impart to the materials a predetermined daytime coloration such as yellow, orange, red or pale shades having such coloration which may be different from that emitted by the phosphorescent substance or substances.

With a composition according to the present invention, it is possible to obtain a stronger daytime coloration using an equal concentration of fluorescent pigments. Moreover products may be obtained which are simultaneously phosphorescent and fluorescent while the natural persistent colour emitted by zinc, calcium or cadmium sulphide will be shifted towards the longer wavelengths of the spectrum.

More especially, the invention relates to materials which comprise ingredients which are required to fulfil a given function, for example, that of building materials or textile materials, as well as a synthetic binder which is transparent from the near ultra-violet to the infra-red and which has a high coefficient of light transmission, and at least one phosphorescent substance, the overall effect being to produce photoluminenscence throughout the whole mass of the said materials, the latter being characterised in that they also contain one or more substances which absorb light energy within the absorption spectrum of the, or one of the phosphorescent substances present, and one or more fluorescent substances. In addition the materials may also include transparent fillers which have a high light transmission from the near ultra-violet to the infra-red.

As an example, materials may be envisaged which contain at least one substance containing an aromatic nucleus, a phosphorescent substance and a fluorescent substance and which enable: 1) The incident spectrum to be shifted so that the ultra-violet component is emitted in the blue region and thus reinforces the incident blue component, for example, by means of antracene.

2) The blue component is then remitted from zinc sulphide for example (or clacium or cadmium sulphides) as a phosphorescent emission, and is thus provided with a prolongedpersistence (greater than 10.8 sec.).

3) A proportion of this persistant emission together with any other incident light (under either daytime or night-time conditions) is then used to excite the fluorescent substance and so imparts a colour characteristic to these emissions (with a persistence less than 10.8 sec.).

The invention will now be described with reference to the accompanying drawings which are given by way of illustration and in which: Figure 1 is a graph showing the absorption curves (hatched areas) and emission curves (unhatched areas) of the constituents of a first composition containing photoluminescent material according to the present invention Figure 2 is a graph of the emission spectrum of the composition of Figure 1 under nighttime conditions, Figure 3 is similar to Figure 1 but relates to a second composition containing a photoluminescent material according to the present invention, and Figure 4 shows various curves for persistence of emission as a function of time.

Referring now to Figure 1, in which wavelengths X are represented along the x axis and the co-efficient of transmission Tr (intensity of emitted light) along the y axis, it can be seen that in addition to transparent fillers and a binder the photoluminescent material contains anthracene (chain-line spectrum), a phosphorescent substance such as zinc sulphide (solid line spectrum), and a fluorescent substance (broken line spectrum). Such a material enables energy to be absorbed in the shorter wavelengths (3000 A to 3800 A) due to the presence of the anthracene and to be emitted (or at least partially emitted, bearing in mind the phosphorescence and fluorescence phenomena) in the longer wavelengths (5800 A to 6800 A) due to the presence of the phosphorescent and fluorescent materials.

As shown in Figure 1, a major proportion of the absorption spectrum of the fluorescent material overlaps with the emission spectrum of the phosphorescent substance (zinc sulphide).

This means that there will be virtually no persistent emission from the zinc sulphide but the fluorescence will be artificially maintained, with a prolonged persistence, utilizing the energy emitted by the zinc sulphide. Such a material will behave as follows: In the daytime the material will appear orange in this example and will have a bright appearance since the fluorescent substance absorbs both a part of the visible light and the light energy absorbed and emitted by both the zinc sulphide and the anthracene.

when the zinc sulphide is wholly or partly replaced by cadmium sulphide, which latter, when pure, emits in the red.

The table below gives the persistent emissivities of various mixtures of zinc sulphide and cadmium sulphide (molar proportions).

Zinc Cadmium Colour of Sulphide (So) Sulphide (SO) Emission 100 0 green 80 20 yellow/green 60 40 yellow 40 60 orange yellow 20 80 orange red 0 100 red Consequently, when a photoluminescent material which emits in the orange-red at night is required, either there is added to the phosphorescent material, which may be zinc sulphide, a fluorescent material which emits in this colour and which has an absorption spectrum which overlaps with the emission spectrum of the phosphorescent material (see Figure 1), or alternatively the zinc sulphide is partly replaced by cadmium sulphide (this latter representing 70 to 80% for example of the mixture of zinc sulphide and cadmium sulphide in this case).

The daytime appearance of such a material will vary depending upon whether the mixture is of zinc sulphide and cadmium sulphide (very intense orange-red persistent emission), of zinc sulphide and a fluorescent material of the kind illustrated in Figure 1 (intense persistent orange emission), or of zinc sulphide and a fluorescent material of the kind illustrated in Figure 3 (moderately intense orange-yellow persistent emission).

There are of course a number of fluorescent materials which could be used and the choice will depend in particular upon their absorption or emission spectra (of the Figure 1 or Figure 3 kind) and upon the colour required.

By way of example, good results have been obtained using pigments which are marketed by Messrs. Marcel Quarre et Cie under the Registered Trade Mark RADGLO. Three pigments are of interest for their colour and for the intensity of their emission peaks.

Orange yellow: emission peak at 5800 A Orange: emission peak at 6000 A Orange red: emission peak at 6200 A Other fluorescent materials have been tested and have proved of some value: these are aromatic substances having five and six aromatic nuclei (pentacene, hexacene). It is, in fact, pentacene which is illustrated in Figure 1.

The use of substances containing such aromatic nuclei is particularly useful when homologous substances having a smaller number of nuclei are used to absorb the shorter wavelengths in the presence of the phosphorescent substance. In such a case, aromatic substances having a larger number or aromatic nuclei are used to form doping agents for those having the smaller number of aromatic nuclei.

Two sequences have been found to be very satisfactory: Anthracene-zinc sulphide-penta- cene (the case illustrated in Figure 1 with the phosphorescent and fluorescent spectra overlapping). Anthracene-zine sulphide-hexacene (the case illustrated in Figure 3 with the phosphorescent and fluorescent spectra lying apart).

The invention will now be described with reference to the following Examples, it being understood that these are in no way of a limiting nature. In the Examples the words 'Protex', 'Rhodopas', 'Texamol', 'Alloprene', 'Cerech lord' and 'Aerosil' are Registered Trade Marks.

EXAMPLE I This example relates to a photoluminescent textile which is obtained by coating using a socalled knife-over-roll system. A typical coating composition is obtained as follows: (a) 800 g of zinc sulphide (the phosphorescent substance) is dissolved in 3% methylcellulose 4000 (2000 g). Solution takes place in the neighbourhood of 30 to 40"C and is effected by stirring.

(b) 2 g of anthracene (the substance which absorbs at shorter wavelenghts than zinc sulphide) and 0.03 g of pentacene (the fluorescent substance) are dissolved in 380 g of 2-propanol.

Solution is effected by heating to reflux at a temperature below 80 C.

(c) Using an immersion stirrer, 2174 g of transparent siliceous fillers are mixed with a resin complex formed from 1000 g of Acrymil 'PROTEX', 30 g of Actiron (catalyst) and 120 g of a plasticiser.

(d) Solutions a and b are mixed, at a temperature of approximately 40oC, by gradually introducing b and a whilst stirring continuously until complete homogenisation is achieved.

(e) Mixture c is then added to solution d.

EXAMPLE 11 The material which forms the subject of this example is particularly useful in the building industry. The operating procedure is as follows: (a) 600 g of zinc sulphide (the phosphorescent substance) is dissolved in 3% methylcellulose, 4000(1200 g). Solution takes place at approximately 30 to 400C and is effected by stirring.

(b) 4 g of anthracene (the substance which absorbs at shorter wavelengths than zinc sulphide) and 0.06 g of pentacene (the fluorescent substance) are dissolved in 760 g of 2-propanol.

Solution is effected by heating to reflux at a temperature below 80QC.

(c) 6000 g of transparent siliceous fillers are mixed, using a stirrer, with a resin complex formed from 2000 g of 'RODOPAS' AM 054 (made by Rhone Poulenc) and 32 g of 'Texanol'.

(d) Solutions a and b are mixed in the neigh At night the material will once again appear orange, although of a more yellow shade, and less brightly than before since the visible light component will no longer be present, it being understood that visible light is that part of the energy spectrum which is available only in the daytime.

It will be realised how useful is such a material which retains its apparent colour both by day and night as a result of photoluminescent phenomena.

Figure 2 shows only the night-time spectrum emitted by the material, the areas of emission being defined by solid lines. This spectrum comprises a moderately intense yellow-green persistent emission due to the zinc sulphide and an orange tinge due to the behaviour of the fluorescent substance. Due to the photoluminescence phenomena the appearance of the material thus lies somewhere between yellowgreen and orange since the colours are additive.

Although the material is less luminous than by day, it is however still perfectly suitable for use as a photoluminescent material.

In Figure 3, in addition to the spectrum of anthracene (chain line), there is shown an emission spectrum for the phosphorescent substance (solid line) such as zinc sulphide, and an absorption spectrum for the fluorescent substance (broken line), in which the two latter lie apart from one another. This means that the energy emitted by the zinc sulphide will not be absorbed by the fluorescent substance as in the case described above. This clearly results in differences in behaviour depending upon whether the material is seen: (a) in the daytime, when the material will appear red as a result of fluorescence, which penomenon will, in this case, completely mask the phosphorescence phenomenon, or (b) at night, when the material will appear yellowish-green as a result of phosphorescence, which is then the only active phenomenon.

This material will thus be particularly useful when a material is required the appearance of which differs by day and night, the different appearances being brought about by photoluminescence phenomena.

Whichever pattern of behaviour is selected, either that of Figure 1 or Figure 3, it is equally possible to make certain alterations to the basic materials as regards those used which transmit at shorter wavelengths than those absorbed by the phosphorescent substance. As has been seen, the material which absorbs at shorter wavelengths which is used in the present case is anthracene, which has three aromatic nuclei.

This substance is particularly useful because its emission spectrum overlaps with the absorption spectrum of the phosphorescent substance (zinc sulphide), thus enabling energy to be transferred from the 3000-3800 A range to the 4500-5200 A range.

It has been found that anthracene may be partly replaced by other substances having similar properties. Particularly beneficial results have been obtained when the aforesaid replacement substance is naphthalene which has two aromatic nuclei. This gives photoluminescent materials in which the constituents absorb at shorter wavelengths than the phosphorescent substance consisting of naphthalene and anthracene. Two advantages accrue from such a mixture.

One advantage is that the total amount of energy emitted by the fluorescent substance is increased. This is due to the fact that the absorptionemission spectrum of naphthalene is further into the ultra violet region than that of anthracene. A certain amount of energy will thus be absorbed by the naphthalene, emitted, then absorbed by the anthracene, with the remainder of the process being as illustrated in either of Figures 1 or 3.

A second advantage is that it is possible to reduce the amount of anthracene used, antracene being an expensive item. Other things being equal, the same results in terms of luminosity continue to be obtained until the molar proportion of anthracene drops to 1 % in relation to the naphthalene, which latter is far less expensive than anthracene. Since the amounts of such ultraviolet absorbers used are already relatively small, it will be appreciated that the anthracene will then only be present in trace proportions.

When the naphthalene and anthracene are used as indicated above, the absorptionemission spectrum obtained will have an absorption range which virtually corresponds to the absorption range in the spectrum of naphthalene and will have an emission range which virtually corresponds to the emission range in the spectrum of anthracene.

It will be appreciated that the presence of anthracene is rendered necessary by the fact that its emission spectrum overlaps with the absorption spectrum of zinc sulphide, which latter acts as the phosphorescent substance.

Depending upon the type of phosphorescent substance which is used, the anthracene may prove to be unnecessary (when the absorption spectrum of the phosphorescent substance is nearer the ultra violet) or is inadequate (the aforesaid absorption spectrum is displaced towards the infra red). In the first case naphthalene is used to solve the problem and the anthracene can be dispensed with, but in the second case it will be necessary to provide, in addition to the anthracene, one or more additional constituents having an absorption spectrum corresponding with the emission spectrum of anthracene and an emission spectrum corresponding with the absorption spectrum of the phosphorescent substance.

Such additional constituents may, for example, be naphthacene and/or pentacene, which respectively have four and five aromatic nuclei.

These constituents are used for example bourhood of 40"C by gradually introducing b into a, whilst stirring continuously, until complete homogenisation is achieved.

(e) mixture c is then added to solution d.

An identical formulation but without the transparent fillers can be used for continuous filament colouring, for example by using a nozzle for the O.P.I. company's process, or any other similar process.

EXAMPLE III The anthracene used in Example II is replaced by a mixture of naphthalene and anthracene, with the molar ratio of anthracene naphthalene being 0.01:1.

The materials obtained in Examples I, II and III all have persistent orange colours.

In the photoluminiscent materials of the present invention, the proportions are preferably as follows: Substances which absorb at shorter wavelengths than the phosphorescent substance: 0.1 to 1% (molar proportion) relative to the synthetic binder.

Phosphorescent substance: 5 to 15% (proportion by weight) relative to the chemical matrix (synthetic binder plus transparent fillers).

Fluorescent substance: 0.1 to 1% (proportion by weight) relative to the phosphorescent substance.

Various tests have been carried out on the amount of illumination provided by the materials of the present invention, and more particularly the textile material of example I.

In this latter case, the textile material was irradiated at 300 lux for 20 seconds and a curve for the intensity of the persistent emission as a function of time was plotted.

This curve appears as a solid line in Figure 4, in which time (in hours) is plotted along the x axis and intensity of persistent emission along they axis. To serve as a comparison, the broken line is a curve for a conventional photoluminescent textile material, that is to say one lacking the material which absorbs at shorter wavelengths than the phosphorescent substance and the fluorescent substance and in which the photoluminescent material applied to the textile contains only zinc sulphide as a photoluminescent substance and is applied in a filmproducing form. Also shown in Figure 4 is a chain-line curve which is a so-called "ideal" curve of a the kind which is associated with the discharge of a battery and towards the solid-line curve should tend.

It is clear from Figure 4 that the initial intensity I'o indicated by the curve for the material of the invention is distinctly higher than that Io indicated by the curve for zinc sulphide and this intensity (solid line) remains higher than that of zinc sulphide for the major part of the time and principally in the period between 5 and 21 hours (which normally represents the limit of the persistence of emission of zinc sulphide).

It has also been found that even better results can be achieved when the substance which absorbs at shorter wavelengths than zinc sulphide is diphenyloxazole, which has the same property as anthracene of absorbing light energy in the ultra-violet region and emitting it at a wavelength within the range in which the phosphorescent substance absorbs light such as zinc sulphide.

This compound diphenyloxazole contains two aromatic nuclei and a heterocyclic ring containing oxygen and nitrogen atoms.

A basic formulation (A) can be produced which contains a synthetic binder, transparent fillers and the remaining requisite ingredients.

This basic fomulation (A) contains, in parts by weight: Synthetic binder: vinyl acetatemaleic ester copolymer 200 Zinc sulphide 54.7 4% Methylcellulose 4000 K 49.5 Texanol 3.2 Methanol 10 Transparent fillers 693 1010.4 The product which absorbs light having the shorter wavelengths is preferably diphenyloxazole (PPO).

The following examples of photoluminescent materials have been produced, the proportions of ultra-violet absorbing and fluorescent materials being expressed in M's (Mole/kg of synthetic binder).

EXAMPLE IV (A) + ultra violet absorber : PPO (10-3 M) fluorescent material : Rhodamine B (8.3.10-6 M) EXAMPLE V (A) + ultra violet absorber : PPO (10-3 M) fluorescent material : Rhodamine B (1.25.10-5 M) EXAMPLE VI (A) + ultra violet absorber : PPO (10-3 M) fluorescent material : Rhodamine B (10-4 M) EXAMPLE VII (A) + ultra violet absorber : PPO (10-3 M) fluorescent material :Rhodamine B (2.10-5 M) + uranin S (10~5 M) Samples of formulation (A), i.e. containing no ultraviolet absorber or fluorescent material and samples of the mixtures of Examples IV, V, VI and VII were tested in the following way: Excitation: 160 lux for 2 minutes Lamp: colour temperature 4200"K The table below summarises the levels of persistent emission obtained as a function of time, the values being expressing in candelas per m2 (Cd/m2).

SAMPLE Persistent Emission after excitation cut-off (cd/m2) 15 min. 30 min. 45 min. 1 hr. l'h hr. 2 hr. 2% her.

FormulationA 0.395 0.253 0.19 0.158 0.123 0.102 0.0917 Example IV ova38 0.275 0.202 0.165 0.125 0.105 0.0933 Example V 0.417 0.257 0.194 0.159 0.121 0.102 0.0915 Example VI 0.401 0.253 0.191 0.156 0.120 0.101 0.0919 Example VII ova04 0.27 0.201 0.165 0.123 0.104 0.0924 The table below summarises the increase in photoluminescence in comparison with conventional phosphorescent products (formulation A), expressed as percentages.

% Difference 15 min. 30 min. 45 min. 1 hr. llk hr. 2 hr. 2her.

Example IV 109 8.69 6.31 4A3 1.62 2.94 1.74 Example V 5.57 1.58 2.1 0.6 -1.6 0 -0.2 Example VI 1.52 0 0 0 0 0 0 Example VII 2.28 6.7 0.55 4.43 0 1.96 0.76 Except in the case of Example VI it will be seen that the increase is considerable, especially in the first minute following extinction (cessation of excitation). In this respect Example IV is quite remarkable since it still shows increased photoluminescence after 2'S hours.The photoluminescent products which form the subject of the present invention are, it should be remembered, chiefly safety materials which need to come into action particularly after illumination is extinguished so as to prevent persons involved from being caught unawares by sudden darkness.

It should be noted that the examples of materials containing anthracene (Examples I to III) similarly show a significant initial increase (cf. Fig. 4).

Depending upon the concentration of the fluorescent substances, daytime colours from creamy white to yellow and orange may be obtained, whereas the colour of formulation A is greenish yellow.

Fluorescein itself has also been employed as a replacement for uranin S.

Another type of material, which lies within the scope of the present invention, has also been produced for use as industrial floors in car-parks and for marking out carriageways.

The composition of this material is as follows, the proportions being by weight: "Alloprene" R20 (a chlorinated rubber) 35 Xylene 65 PPO (ultraviolet absorber) 0.022 (10-3 M) Rhodamin B (fluorescent material) 4.79 10-5 (10$ M) "Aerosil" 200 0.5 "Cerechlor" 42 17.5 Methylethyl Ketone 25 Zinc sulphide 40 Glass spheres (transparent fillers) Type C63.200 190.5 Type 250.630 127 500.5 These good results are the consequence of a combination of two factors, namely, firstly a bulk effect from the material, since light is able to penetrate through the material owing to the use of the transparent fillers, and secondly an energy transfer effect resulting from the overlap between the emission spectrum of the ultra violet absorber(s) and the spectrum of the phosphorescent substance or substances, and possibly from the overlap between the emission spectrum of the phosphorescent substance or substances and of the absorption spectrum of the fluorescent substance or substances.

WHAT WE CLAIM IS: 1. Materials which are photoluminescent throughout, of the kind which include a synthetic binder which is transparent from the near ultra-violet to the infrared and which has a high co-efficient of light transmission, and at least one phosphorescent substance, in which there is also present one or more substances which absorb light energy in the ultra-violet region and emit light energy within the absorption spectrum of the, or one of the, phosphorescent substances present, as well as one or more fluorescent substances.

2. A material according to claim 1 which also includes transparent fillers having a high light transmission within the same spectral range as the synthetic binder.

3. A material according to either of claims 1 or 2, in which said fluorescent substance absorbs light within the emission spectrum of the phosphorescent substance.

4. A material according to either of claims 1

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (23)

**WARNING** start of CLMS field may overlap end of DESC **. The table below summarises the levels of persistent emission obtained as a function of time, the values being expressing in candelas per m2 (Cd/m2). SAMPLE Persistent Emission after excitation cut-off (cd/m2) 15 min. 30 min. 45 min. 1 hr. l'h hr. 2 hr. 2% her. FormulationA 0.395 0.253 0.19 0.158 0.123 0.102 0.0917 Example IV ova38 0.275 0.202 0.165 0.125 0.105 0.0933 Example V 0.417 0.257 0.194 0.159 0.121 0.102 0.0915 Example VI 0.401 0.253 0.191 0.156 0.120 0.101 0.0919 Example VII ova04 0.27 0.201 0.165 0.123 0.104 0.0924 The table below summarises the increase in photoluminescence in comparison with conventional phosphorescent products (formulation A), expressed as percentages. % Difference 15 min. 30 min. 45 min. 1 hr. llk hr. 2 hr. 2her. Example IV 109 8.69 6.31 4A3 1.62 2.94 1.74 Example V 5.57 1.58 2.1 0.6 -1.6 0 -0.2 Example VI 1.52 0 0 0 0 0 0 Example VII 2.28 6.7 0.55 4.43 0 1.96 0.76 Except in the case of Example VI it will be seen that the increase is considerable, especially in the first minute following extinction (cessation of excitation). In this respect Example IV is quite remarkable since it still shows increased photoluminescence after 2'S hours.The photoluminescent products which form the subject of the present invention are, it should be remembered, chiefly safety materials which need to come into action particularly after illumination is extinguished so as to prevent persons involved from being caught unawares by sudden darkness. It should be noted that the examples of materials containing anthracene (Examples I to III) similarly show a significant initial increase (cf. Fig. 4). Depending upon the concentration of the fluorescent substances, daytime colours from creamy white to yellow and orange may be obtained, whereas the colour of formulation A is greenish yellow. Fluorescein itself has also been employed as a replacement for uranin S. Another type of material, which lies within the scope of the present invention, has also been produced for use as industrial floors in car-parks and for marking out carriageways. The composition of this material is as follows, the proportions being by weight: "Alloprene" R20 (a chlorinated rubber) 35 Xylene 65 PPO (ultraviolet absorber) 0.022 (10-3 M) Rhodamin B (fluorescent material) 4.79 10-5 (10$ M) "Aerosil" 200 0.5 "Cerechlor" 42 17.5 Methylethyl Ketone 25 Zinc sulphide 40 Glass spheres (transparent fillers) Type C63.200 190.5 Type 250.630 127 500.5 These good results are the consequence of a combination of two factors, namely, firstly a bulk effect from the material, since light is able to penetrate through the material owing to the use of the transparent fillers, and secondly an energy transfer effect resulting from the overlap between the emission spectrum of the ultra violet absorber(s) and the spectrum of the phosphorescent substance or substances, and possibly from the overlap between the emission spectrum of the phosphorescent substance or substances and of the absorption spectrum of the fluorescent substance or substances. WHAT WE CLAIM IS:

1. Materials which are photoluminescent throughout, of the kind which include a synthetic binder which is transparent from the near ultra-violet to the infrared and which has a high co-efficient of light transmission, and at least one phosphorescent substance, in which there is also present one or more substances which absorb light energy in the ultra-violet region and emit light energy within the absorption spectrum of the, or one of the, phosphorescent substances present, as well as one or more fluorescent substances.

2. A material according to claim 1 which also includes transparent fillers having a high light transmission within the same spectral range as the synthetic binder.

3. A material according to either of claims 1 or 2, in which said fluorescent substance absorbs light within the emission spectrum of the phosphorescent substance.

4. A material according to either of claims 1

or 2, in which said fluorescent substance absorbs light outside the emission spectrum of the phosphorescent substance.

5. A material according to any of the preceding claims, in which said fluorescent substance is ah aromatic compound having a plurality of nuclei.

6. A material according to claim 5, in which the phosphorescent substance is zinc sulphide and the aromatic compound is pentacene.

7. A material according to claim 5, in which the phosphorescent substance is zinc sulphide and the aromatic compound is hexacene.

8. A material according to either of claims 1 or 2, in which the phosphorescent substance is zinc sulphide, and the substance which absorbs light in the ultra violet region is antracene.

9. A material according to claim 8, in which the antracene is partly replaced by naphthalene, the molar ratio of antracene to naphthalene being of the order of l 0-3 to 102:1.

10. A material according to any one of claims 1 to 9, in which the phosphorescent substance is at least in part replaced by an additional phosphorescent substance.

11. A material according to claim 10, in which the said additional substance is cadmium sulphide and the essential phosphorescent substance is zinc sulphide.

12. A material according to either of claims 1 or 2, which contains 0.1 to 1 molar percent of substance(s) which absorb in the ultraviolet region relative to the synthetic binder, 5 to 15% by weight of phosphorescent substance(s) relative to the chemical matrix (synthetic binder plus transparent fillers), and 0.1 to 1% by weight of fluorescent substance(s) relative to the phosphorescent substance(s).

13. A material according to any of claims 1 to 4, in which the phosphorescent substance is zinc sulphide and the substance which absorbs in the ultra violet region is diphenyloxazole.

14. A material according to claim 13, in which the concentration of diphenyloxazole is l0-3 mole per kg of synthetic binder.

15. A material according to either of claims 13 and 14, in which the fluorescent material is rhodamine B and/or uranin S.

16. A material according to claim 15, in which the concentration of the fluorescent material is from 10.6 to 10-4 mole per kg of synthetic binder.

17. A material according to any one of claims 13 to 16, which contains substantially 20% by weight of a synthetic binder such as a vinyl acetate-maleic ester co-polymer and 70% by weight of transparent fillers.

18. A method of obtaining a product according to any one of claims 1 to 17, which comprises: (a) dispersing the phosphorescent substance or substances, and (b) dissolving the substance(s) which absorb in the ultra violet region and the fluorescent substance, in a solvent therefor, (c) introducing solution b into solution a and mixing until homogenised, (d) mixing the mixture obtained under c with the synthetic binder.

19. A method as claimed in claim 18 in which the synthetic resin is admixed with transparent fillers prior to mixing with the mixt Ire obtained under (c).

20. A method according to either of claims 18 or 19, in which the phosphorescent substance is zinc sulphide and the dispersion is effected in methylcellulose, preferably at a temperature of 30 to 40"C.

21. A method according to any of claims 18 to 20, in which the substance which absorbs in the ultra violet region is antracene alone or admixed with naphthalene and the fluorescent substance is pentacene and solution is effected in 2-propanel, preferably at a temperature below 800C.

22. A photoluminescent material according to claim 1 , and substantially as hereinbefore described with reference to any one of the Examples.

23. A method of obtaining a photoluminescent material according to claim 18 or claim 19 and substantially as hereinbefore described with reference to any of the Examples.