PHOTOLUMINESCENT MARKERS

Abstract

A marker for illuminating an area of an aircraft, the marker including a photoluminescent material arranged to emit blue visible light in response to an excitation and wherein the photoluminescent material has an emission spectrum with a maximum peak intensity of from 450 nm to 510 nm and optionally substantially 490 nm. The photoluminescent material has a performance characteristic such that the emissivity is at least 0.3 mcd/m.sup.2 12 hours after cessation of charging at 25 lux for 45 mins optionally at least 30 mcd/m.sup.2 6 hours after cessation of charging. The photoluminescent material comprises at least a main pigment containing a Europium and Dysprosium doped strontium aluminate with the formula Sr.sub.4Al.sub.14O.sub.25:Eu,Dy and optionally one or more further phosphorescent pigments. A marker system is disclosed for illuminating areas of an aircraft, the system including a plurality of markers in accordance with the invention. Also disclosed is an aircraft including a passenger cabin; and a marker system as disclosed.

Claims

1. A marker for illuminating an area of an aircraft, the marker including a photoluminescent material arranged to emit blue visible light in response to an excitation and wherein the photoluminescent material has an emission spectrum with a maximum peak intensity between 400 nm and 510 nm.

2. The marker of claim 1 wherein the photoluminescent material is arranged to emit blue visible light in response to excitation by light of wavelength between 450 nm and 500 nm.

3. A marker according to claim 1 or claim 2 wherein the photoluminescent material has a performance characteristic such that the emissivity is at least 0.3 mcd/m.sup.2 12 hours after cessation of charging at 25 lux for 45 mins and preferably at least 0.3 mcd/m.sup.2 16 hours after cessation of charging at 25 lux for 45 mins and optionally at least 30 mcd/m.sup.2 after 12 hours, or more preferably after 16 hours, after cessation of charging at 25 lux for 45 mins.

4. A marker according to claim 3 wherein the emissivity intensity, 10 minutes after charging is terminated, is at least 50 mcd/m.sup.2 or more preferably at least 150 mcd/m.sup.2 or most preferably at least 300 mcd/m.sup.2 according to DIN67510.

5. A marker in accordance with any preceding claim wherein the photoluminescent material comprises a pigment containing a Europium and Dysprosium doped strontium aluminate.

6. A marker in accordance with claim 5 wherein the photoluminescent material comprises at least a main pigment containing a Europium and Dysprosium doped strontium aluminate with the formula Sr.sub.4Al.sub.14O.sub.25:Eu,Dy.

7. A marker in accordance with claim 6 wherein the photoluminescent material comprises the main pigment and at least one further pigment.

8. A marker in accordance with claim 5 wherein the pigment comprises from 50 wt % to 100 wt % of Sr.sub.4Al.sub.14O.sub.25:Eu,Dy.

9. The marker of any preceding claim wherein the photoluminescent material is excited by visible or non-visible light.

10. A marker according to any preceding claim wherein the photoluminescent material has an emission spectrum with a maximum peak intensity between 485 nm to 495 nm and optionally substantially at 490 nm.

11. The marker of any preceding claim wherein the pigment comprises particles of pigment having a range of sizes and wherein the particles are from 1 to 200 microns in size.

12. The marker of claim 11 wherein the particles range from 5 to 90 microns.

13. The marker of any preceding claim further including a cover provided over at least a top surface of the photoluminescent material.

14. The marker of claim 13 wherein the cover is at least partially transparent to the blue light emitted by the photoluminescent material.

15. The marker of claim 13 or claim 14 wherein the cover is at least partially transparent to the excitation required to stimulate the blue emission.

16. The marker of any preceding claim wherein the photoluminescent material comprises at least a main pigment containing a Europium and Dysprosium doped strontium aluminate with the formula Sr.sub.4Al.sub.14O.sub.25:Eu,Dy and optionally one or more further phosphorescent pigments.

17. The marker of any of claims 14 wherein the or each further pigment is a doped metal aluminate.

18. The marker of claim 14 wherein the doped metal aluminate comprises a dopant selected from the list comprising: europium ions; dysprosium ions; and neodymium ions or any other rare earth (lanthanide) ions.

19. The marker of claim 18 wherein the photoluminescent material comprises a mixture of the main pigment and a pigment comprising at least one of SrAl.sub.4O.sub.7Eu,Dy or CaAl.sub.2O.sub.4:Eu,Nd; and SrAl.sub.2O.sub.4:Eu,Dy.

20. The marker of any one of claims 16 to 19 wherein the photoluminescent material comprises a plurality of pigments, each pigment emitting a different colour of light in response to the excitation, such that the light emitted by the photoluminescent material comprises a mixture of colours forming an emission spectrum having a range from 400 nm to 510 nm.

21. A marker in accordance with any preceding claim wherein the marker further comprises a coloured filter

22. A marker in accordance with any preceding claim wherein the marker further comprises a housing.

23. A marker system for illuminating areas of an aircraft, the system including a plurality of markers according to any of claims 1-22.

24. The system of claim 23 further including markers including a photoluminescent material arranged to emit blue visible light in response to an excitation.

25. The system of claim 23 or claim 24, wherein the system includes a group of first markers.

26. The system of claim 25 wherein the first markers are emergency markers highlighting locations and/or routes to one or more emergency exits of an aircraft.

27. The system of claim 23 wherein the system includes a group of second markers which comprise seat markers.

28. The system of claims 23 to 27 wherein the system is arranged to provide an emergency evacuation guide and wherein at least the first markers are formed as elongate track sections and wherein the tracks are can be secured to a floor a floor of an aircraft cabin to direct passengers from their seat to the nearest emergency exit.

29. An aircraft including a passenger cabin; and a marker system according to any of claims 23 to 28.

30. An aircraft according to claim 29 wherein the marker system comprises a number of markers wherein the photoluminescent material comprises at least a main pigments emitting light in response to excitation, such that the light emitted by the photoluminescent material comprises an emission spectrum having a peak within a range from 400 nm to 510 nm.

31. An aircraft according to claim 29 or claim 30 wherein the marker system comprises a photoluminescent material having at least a main pigment comprising Sr.sub.4Al.sub.14O.sub.25:Eu,Dy.

Description

[0074] Embodiments of the invention will now be described by way of example only, with reference to the drawings, in which:

[0075] FIG. 1 illustrates the electromagnetic spectrum;

[0076] FIG. 2 illustrates the ranges of vision regimes and receptor regimes in the human eye;

[0077] FIG. 3 illustrates the receptor sensitivities in the human eye;

[0078] FIG. 4 illustrates absorption spectra of human eye rods overlaid with emission profile of blue and green emitting photoluminescent material overlaid with dark blue film;

[0079] FIG. 5 illustrates a schematic example of a marker in plan view;

[0080] FIG. 6 illustrates a cross-section through the marker of FIG. 5;

[0081] FIG. 7A illustrates the excitation and emission curves for a first example photoluminescent pigment;

[0082] FIG. 7B illustrates the excitation and emission curves for a second example photoluminescent pigment, Sr.sub.4Al.sub.14O.sub.25: Eu.sup.2+,Dy.sup.3+;

[0083] FIG. 7C illustrates the excitation and emission curves for a third example photoluminescent pigment;

[0084] FIG. 8 illustrates the excitation curve for a marker including a fourth example photoluminescent material;

[0085] FIG. 9 illustrates a schematic example of a cabin of an aircraft, incorporating an emergency exit marking system; and

[0086] FIGS. 5 and 6 show a schematic example of a marker 100 in accordance with the invention. The marker 100 shown in FIGS. 5 and 6 is a simple rectangular marker 100, shown for illustrative purposes only. As will be discussed in further detail below, the marker may have any suitable shape or configuration.

[0087] The marker 100 shown in FIGS. 5 and 6 comprises a housing 106, of rectangular cross section with a bottom wall 106a, side walls 106b and a top wall 106c. The housing 106 can be formed by any suitable method, and is made of a light transmitting material. A photoluminescent insert 108 is received in the housing 106, and extends from one end of the housing 106 to the other. The housing 106 is closed by end caps 106d or sealant. The photoluminescent insert 108 is a push fit inside the housing 106, and includes a substrate 102, and a region of photoluminescent material 104 covering the surface of the substrate 102 that faces up in use. The photoluminescent material 104 exhibits persistent luminescence (phosphorescence).

[0088] In other embodiments (not shown), a marker may comprise at least one photoluminescent layer and at least one protective layer covering the photoluminescent layer where the photoluminescent layer comprises photoluminescent material and the protective layer comprises a light transmitting material. Such a marker may be used as a seat marker or an exit marker. The marker may also comprise colour filters as part of the housing or provided as a film within the housing.

[0089] A photoluminescent material is a material that emits radiation in response to an excitation, for example irradiation by a light source (visible or not visible). The light source may be providing UV light. A material exhibiting persistent luminescence emits radiation for a sustained period of time in response to excitation. This means that even if the excitation is removed, the marker will continue to emit visible light. Therefore, if the cabin 200 becomes dark (either the lights are switched off for passenger comfort, the lights lose power in an emergency, or the cabin is filled with smoke), the marker 100 is still visible.

[0090] The region of photoluminescent material 104 in the marker 100 of FIGS. 5 and 6 includes one or more phosphorescent pigments, the main pigment is Sr.sub.4Al.sub.14O.sub.25:Eu.sup.2+,Dy.sup.3+ and optionally at least one additional pigment. The additional pigments used are doped metal aluminates, of the form M.sub.xAl.sub.yO.sub.z:D1.sup.2+D2.sup.3+ where M is a metal, D1 and D2 are dopants, and x:y:z the ratio of the metal, aluminium and oxygen in the pigment, also referred to as the stoichiometry of the pigment. The Sr.sub.4Al.sub.14O.sub.25:Eu.sup.2+,Dy.sup.3+ has a spectrum of emissivity with a maximum peak of emissivity at about 490 nm.

[0091] The photoluminescent material may further comprise an additional pigment. The additional pigment also comprises a doped metal aluminate. The metal may be, for example, Strontium, Calcium or any alkali or alkaline earth metal. The dopant may be, for example, Europium ions, Dysprosium ions, Neodynium ions, or rare earth (lanthanide) ions. In a particular embodiment the dopant is Europium ions and Dysprosium ions. The dopant is typically less than 1% by weight of the composition. In a preferred composition the main pigment comprises Sr.sub.4Al.sub.14O.sub.25:Eu.sup.2+,Dy.sup.3+. The additional pigment is one of SrAlO.sub.4 or SrAl.sub.4O.sub.7. An additional pigment could alternatively be CaAlO.sub.4:Eu,Nd.

[0092] The colour of light emitted by a pigment is controlled by the stoichiometry. Therefore, the colour of the region of photoluminescent material 104 can be controlled by using either a single pigment of a chosen colour, or a mixture of pigments of different colours. This can be used to a generate range of emitted colours. It is important that the wavelength of the emitted light are in the range from 400 nm to 510 nm but desirably in the range 485 nm to 495 nm.

[0093] Table 2 show examples of pigments that can be used in the region of photoluminescent material 104 of the marker 100 in FIGS. 5 and 6. The emission from the pigment is typically a spectrum of light. Table 2 shows the maximum of the emission spectrum from a pigment (for example P1), although the emission of some pigments (for example P3) is reported over a range of wavelengths.

TABLE-US-00002 TABLE 2 Example pigments. Material Emission Colour P1 SrAl.sub.2O.sub.4:Eu.sup.2+, Dy.sup.3+ 520 nm Green P2 SrAl.sub.4O.sub.7:Eu.sup.2+, Dy.sup.3 480 nm Blue P3 SrAl.sub.12O.sub.19:Eu.sup.2+, Dy.sup.3 400-500 nm Blue P4 Sr.sub.2Al.sub.6O.sub.11:Eu.sup.2+, Dy.sup.3 400-500 nm Blue P5 Sr.sub.3Al.sub.2O.sub.6:Eu.sup.2+, Dy.sup.3 612 Red P6 Sr.sub.4Al.sub.2O.sub.7:Eu.sup.2+, Dy.sup.3 350-700 nm Blue-red P7 Sr.sub.4Al.sub.14O.sub.25:Eu.sup.2+, Dy.sup.3+ 490 nm Blue-green P8 Sr.sub.7Al.sub.12O.sub.25:Eu.sup.2+, Dy.sup.3 410-460 nm Violet-green P9 CaAl.sub.2O.sub.4:Eu.sup.2+, Nd.sup.3+ 440 nm Violet

[0094] Table 3 shows examples of mixtures of pigments that can be used in the region of photoluminescent material 104 of the marker 100 in FIGS. 5 and 6. The constituent pigments are taken from Table 2.

TABLE-US-00003 TABLE 3 Example mixtures. Mixture Ratio Colour M1 P1 and P7 1:9 Cyan M2 P1 and P7 2:8 Cyan

[0095] Other mixtures may be used: P1 and P2; P1 and P9. It is possible to use a number of mixtures and ratios such that the light emitted does not have a wavelength greater that 510 nm.

[0096] In a one embodiment the ratio of SrAl.sub.2O.sub.4: Eu.sup.2+,Dy.sup.3+: Sr.sub.4Al.sub.14O.sub.25: Eu.sup.2+,Dy.sup.3+ is 1:1. In a more preferred embodiment the pigments may be comprise between 1:1 and 99:1 Sr.sub.4Al.sub.14O.sub.25: Eu.sup.2+,Dy.sup.3+: Dy.sup.3+: SrAl.sub.2O.sub.4: Eu.sup.2+,Dy.sup.3+. In the most preferred embodiment the pigment comprises 100% Sr.sub.4Al.sub.14O.sub.25:Eu.sup.2+,Dy.sup.3+. It will be appreciated that the pigment may comprise minor amounts of impurities or contaminants.

[0097] FIG. 7A shows the excitation spectra (also known as the charging profile) of pigment P1 as line 300a and the emission spectra of pigment P1 as line 302a, as an example. The P1 excitation spectra 300a shows the wavelengths of light required to excite pigment P1 to emit. The P1 emission spectra, 302a shows the spectrum of light emitted by the pigment. The difference in the wave length between the excitation wavelength and the emitted wavelength is known as the Stokes shift.

[0098] Similarly, FIG. 7B shows the excitation spectra of pigment P7 300b, and the emission spectra of pigment P7 302b as another example. P7 is Sr.sub.4Al.sub.14O.sub.25:Eu,Dy. FIG. 7C shows the excitation spectra of pigment P9 300c, and the emission spectra of pigment P9 302c, as a further example.

[0099] The P9 charging profile 300c is largely in the ultraviolet (UV) region of the electromagnetic spectrum (wavelength of 100 nm to 400 nm), with no excitation above 400 nm. Both P1 and P7 also have the majority of the charging profile 300a, 300b in the UV region too, with some of the profile above 400 nm. In some embodiments it can be desirable to arrange for the photoluminescent material to be charged by UV radiation. It can be advantageous as UV radiation can be emitted without disturbing sleeping passengers on an overnight flight. Blue light may also be used for charging the photoluminescent material. Blue light may be used to illuminate the cabin particularly during night flights.

[0100] A charging profile of Sr.sub.4Al.sub.14O.sub.25:Eu,Dy is provided in FIG. 7B.

[0101] The housing 106 and pigment (or mixture of pigments) should be selected so that the housing 106 is transparent to at least a portion of the charging profile 300, and the transmission profile 302. FIG. 8 shows an example of the charging profile 300d for a mixture of pigments that emits blue light. In this example, the majority of the charging profile 300d is again in the UV, with some charging above 400 nm.

[0102] FIG. 8 also shows an example transmission curve 304 for the housing 106. The housing 106 allows transmission of light starting at approximately 390 nm and above, and blocks light below this. The charging curve 300d for the mixture of pigments, is modified by the transmission curve 304, to give a marker charging curve 306. This is the wavelengths of light required to excite the marker to emit light. This is different to the charging curve for the mixture 300d because of the transmission of the housing 106.

[0103] A housing 106 with a different transmission curve would be required for pigments with different charging curves (for example P9), to ensure that the blue emission is excited.

[0104] The emission colour of the marker 100 can be controlled by selecting the pigment or mixture of pigments used in the region of photoluminescent material 104. For example, the marker 100 can be made non-green by using a single non-green pigment on its own (see Table 2). Alternatively, a mixture of pigments from Table 2 can be used, with the final appearance of the mixture being blue (see Table 3). Although the final appearance of the mixture of pigments may be blue, the mixture may include a pigment that emits green light.

[0105] The advantages of the invention are achieved by selecting a number of pigments that have an overall blue emission and that have an emission intensity characteristic that is from preferably from 485 to 495 nm and is centred on 490 nm. In some cases the overall emission may be adjusted such that the range is from 480 nm to 500 nm.

[0106] In the above, emission is considered to be green if it has a peak between 510 nm and 530 nm, and non-green if its peak is outside this range.

[0107] DIN65710 requires that the intensity emissivity has to be greater than 0.3 mcd/m.sup.2 for photoluminescent materials which is 100 times the human eye sensitivity.

[0108] The marker 100 may be used in many different ways, and the colour of the marker 100 may be changed for the different scenarios. The marker 100 can also include a design. The design may be wording, symbols, logos or the like. The marker can also be made any shape.

[0109] The design can be formed by changing the shape of the region of photoluminescent material 104. In addition, or alternatively, the housing 106 or protective layer(s) may be constructed to provide the pattern, by only allowing transmission of the excitation light and/or the emitted light in certain regions. This may be by means of a coating or cover layer provided on the housing 106 or protective layer(s), or making the housing 106 or protective layer(s) of regions of different material.

[0110] In one example, markers 100 may be used in an emergency exit marking system 300, as shown in FIG. 9. In this case, the pigment, or mixture of pigments are chosen to have a sufficient excitation profile between 400 nm and 500 nm for charging and to provide a blue emission from UV to blue visible light. The wavelengths from 400 nm to 500 nm of light are available in dark or low light environments in an aircraft in order to charge the pigments. The pigment and transmission curve of the housing are also chosen to ensure blue light is emitted. For example, the light may be emitted at 490 nm. The housing is arranged to be transparent or partially transparent to light emitted by the pigment in the marker.

[0111] For emergency exit marking national and international aviation standards provide standards of duration and brightness of the emission after the excitation is removed (afterglow brightness and duration), such that all passengers have time to safely exit the aircraft in an emergency as may be evidenced by naive evacuation examples. The marker 100 must also be visible in the dark.

[0112] FIG. 4 shows the response of the human eye to light, under low light and dark conditions. As has been discussed the human eye after a period of time in dark conditions can utilise scotopic vision in which the eye uses rod cells to detect light. In these scotopic conditions, the eye is most responsive at 498 nm. For an emergency exit system 300, the markers and pigments should be selected to emit light that the human eye is responsive to when dark adapted. (i.e. using Scotopic vision)

[0113] FIG. 9 shows a schematic example of a section of a passenger cabin 200 of an aircraft, formed between fuselage walls 202. The cabin 200 includes rows of seating 204, arranged with an aisle 206 through the rows 204. Emergency exits 208a, 208b are provided in the fuselage walls 202. Access paths 210a, 210b are provided between a first row of seats 204a and a second row of seats 204b, to allow access to the emergency exits 208a, 208b, from the aisle 206.

[0114] Markers 100 are formed as elongate track sections 100. The track sections 100 are laid end to end (and around corners) to form tracks, each of several sections 100 length. The tracks are provided on the floor of the aisle 206 and access paths 210a, 210b, to direct passengers from their seat to the nearest emergency exit 208a, 208b.

[0115] Markers 100 may also be formed into signs to mark the locations of the emergency exits 208 either above the exit or at low level. The markers 100 may also provide emergency marking of seats, footrests, monuments and other fixtures or fittings in the aircraft.

[0116] In some examples, the marker 100 may also be used to provide daylight colours. The mixtures of pigments may be used to provide whiter daylight colours than currently available. The daylight colour refers to the appearance of the marker in daylight.

[0117] In some examples, the marker 100 may include two different pigments or mixtures of pigmentsa first pigment or mixture that emits a first wavelength of light in response to UV light excitation, and a second pigment or mixture that emits a second wavelength of light in response to daylight excitation. In this way, the marker 100 can be made to have a different appearance in light conditions compared to no light or dark conditions.

[0118] In some examples, the housing 106 may form a protective layer or top cover. For example, the protective layer may prevent damage from passengers walking on the marker 100. In other examples, a separate protective layer may be provided. The protective layer and/or housing may be used to provide a matt or gloss finish to the marker 100. In other examples a colour modifier in the form of a colour filter may be used. This may be applied to the protective layer or top cover or may form part of the marker. In some embodiments the marker comprises a housing in which the photoluminescent material is provided. The housing may comprise a colour modifier in the housing. The colour modifier can be a colouring in the housing.

[0119] The above pigments are given by way of example only, and other types of aluminate and non-aluminate based phosphorescent materials will be apparent to the person skilled in the art that can be mixed to provide a photoluminescent material having an emission spectra in the range 400-510 nm.

[0120] It will be appreciated that the structure shown in FIGS. 5 and 6 is by way of example only. Any suitable construction may be used to provide a photoluminescent marker 100, and many different possible constructions will be apparent to the person skilled in the art. For example, only the top part of the housing 106c may be formed of the transparent material.

[0121] It will also be appreciated that the cabin shown in FIG. 9 is also by way of example only, and the floorpath system may be used with any suitable passenger cabin arrangement.

[0122] It will be appreciated that the markers could also be used in any type of vehicle, such as a bus or boat, and could also be used in buildings. It will be appreciated that the markers are particularly suited to use in aircraft.