Use of transition-metal oxide nanoparticles as sensitive materials in chemical sensors for detecting or assaying vapors of target molecules

Abstract

The invention relates to the use of nanoparticles of at least one oxide of at least one transition metal doped with a rare earth element, particularly Y.sub.xVO.sub.4Eu.sub.1-x nanoparticles obtained through a sol-gel process, as a sensitive material in a chemical sensor for detecting peroxide-compound vapors. The material is used in a liquid process, in a spray of the initial sol, or in a solid thin film after being deposited on a substrate. The inorganic, fluorescent character of the nanoparticles makes it possible to obtain a sensitive material for an optical sensor that has good performance stability over time. The intended uses are the detection of explosives or explosive precursors, particularly peroxides, the control or monitoring of atmospheric pollution and ambient-air quality, and the monitoring of industrial sites.

Claims

1. A method for detecting or assaying vapors of one or more target compound(s) or molecule(s) comprising utilizing nanoparticles of at least one oxide of at least one transition metal doped with a rare earth element, obtained through a sol-gel process, as a sensitive material in a chemical sensor; wherein the nanoparticles are present in the chemical sensor in the form of a solid thin film of nanoparticles of a thickness of 2 nanometers to one micrometer, and wherein said one or more target compound(s) or molecule(s) is (are) detected or assayed by measuring variations of physical property(ies) of the solid thin film of nanoparticles induced by the presence of said one or more target compound(s) or molecule(s).

2. The method of claim 1, wherein the thin film is prepared directly by wet process by deposition of an aqueous sol which is the sol from which the nanoparticles have been obtained.

3. The method of claim 1, wherein the solid thin film of nanoparticles covers at least in part one or both faces of a flat substrate.

4. The method of claim 1, wherein the solid thin film of nanoparticles has a thickness of 100 nm to 300 nm.

5. The method of claim 1, wherein the solid thin film of nanoparticles is a mesoporous film.

6. The method of claim 1, wherein the solid thin film of nanoparticles has a specific surface area of 100 m.sup.2/g to 200 m.sup.2/g, measured by BET.

7. A method for detecting or assaying vapors of one or more target compound(s) or molecule(s) comprising utilizing nanoparticles of at least one oxide of at least one transition metal doped with a rare earth element, obtained through a sol-gel process, as a sensitive material in a chemical sensor; wherein the nanoparticles are present in the chemical sensor in the form of a sol of nanoparticles in a solvent, and wherein said one or more target compound(s) or molecule(s) is (are) detected or assayed by measuring variations of physical property(ies) of the sol of nanoparticles in a solvent induced by the presence of said one or more target compound(s) or molecule(s).

8. The method of claim 7, wherein the sol of nanoparticles has a concentration of nanoparticles of 0.01% to 4% by weight.

9. The method of claim 7, wherein the solvent is selected from the group consisting of water, organic solvents; and mixtures thereof.

10. The method of claim 7, wherein the sol of nanoparticles is sprayed in the form of a jet, nebulisate or spray.

11. The method of claim 7, wherein the sol of nanoparticles is in the form of a thin film.

12. The method of claim 11, wherein the thin film of the sol of nanoparticles has a thickness of 2 nanometers to one micrometer.

13. The method of claim 1, wherein the nanoparticles are nanoparticles of Y.sub.xVO.sub.4Eu.sub.1-x, where x has a value of 0 to 0.995.

14. The method of claim 1, wherein the nanoparticles are selected from the group consisting of nanoparticles of EuVO.sub.4, and nanoparticles of Y.sub.0.5VO.sub.4Eu.sub.0.5.

15. The method of claim 1, wherein the nanoparticles have a diameter of 2 to 100 nm.

16. The method of claim 1, wherein the nanoparticles of at least one oxide of at least one transition metal doped with a rare earth element are each covered with a thin layer of silica obtained through a sol-gel process.

17. The method of claim 16, wherein the thin layer of silica has a thickness of 1 to 10 nanometers.

18. The method of claim 16, wherein the silica is functionalized by chemical groups.

19. The method of claim 1, wherein the chemical sensor is a gravimetric sensor.

20. The method of claim 1, wherein the chemical sensor is a fluorescence optical sensor.

21. The method of claim 1, wherein the sensor is a multisensor comprising several elementary sensors selected from fluorescence optical sensors and gravimetric sensors, at least one among said elementary sensors being a sensor that comprises nanoparticles of at least one oxide of at least one transition metal doped with a rare earth element, obtained through a sol-gel process, as a sensitive material.

22. The method of claim 1, wherein the target compound(s) or molecules(s) are selected from the group consisting of atmospheric pollutants, explosives and precursors of explosives.

23. The method of claim 1, wherein the target compound(s) or molecules(s) are selected from peroxides.

24. The method of claim 23, comprising detecting or assaying peroxides vis--vis volatile organic compounds.

25. The method of claim 23, wherein the target compound(s) or molecules(s) are selected from the group consisting of hydrogen peroxide, hydroperoxides, and peroxides of ketones.

26. A chemical sensor comprising nanoparticles of at least one oxide of at least one transition metal doped with a rare earth element, obtained through a sol-gel process, as a sensitive material; in which the nanoparticles are present in the chemical sensor in the form of a solid thin film of nanoparticles of a thickness of 2 nanometers to one micrometer.

27. A chemical sensor comprising nanoparticles of at least one oxide of at least one transition metal doped with a rare earth element, obtained through a sol-gel process, as a sensitive material; in which the nanoparticles are present in the chemical sensor in the form of a sol of nanoparticles in a solvent.

28. The chemical sensor according to claim 26, wherein the chemical sensor is a gravimetric sensor.

29. The chemical sensor according to claim 27, wherein the chemical sensor is a gravimetric sensor.

30. The chemical sensor according to claim 26, wherein the chemical sensor is a fluorescence sensor.

31. The chemical sensor according to claim 27, wherein the chemical sensor is a fluorescence sensor.

32. The chemical sensor according to claim 26, wherein the chemical sensor detects hydrogen peroxide.

33. The chemical sensor according to claim 27, wherein the chemical sensor detects hydrogen peroxide.

34. The method of claim 7, wherein the nanoparticles are nanoparticles of Y.sub.xVO.sub.4Eu.sub.1-x, where x has a value of 0 to 0.995.

35. The method of claim 7, wherein the nanoparticles are selected from the group consisting of nanoparticles of EuVO.sub.4, and nanoparticles of Y.sub.0.5VO.sub.4Eu.sub.0.5.

36. The method of claim 7, wherein the nanoparticles have a diameter of 2 to 100 nm.

37. The method of claim 7, wherein the nanoparticles of at least one oxide of at least one transition metal doped with a rare earth element are each covered with a thin layer of silica obtained through a sol-gel process.

38. The method of claim 37, wherein the thin layer of silica has a thickness of 1 to 10 nanometers.

39. The method of claim 37, wherein the silica is functionalized by chemical groups.

40. The method of claim 7, wherein the chemical sensor is a gravimetric sensor.

41. The method of claim 7, wherein the chemical sensor is a fluorescence optical sensor.

42. The method of claim 7, wherein the sensor is a multisensor comprising several elementary sensors selected from fluorescence optical sensors and gravimetric sensors, at least one among said elementary sensors being a sensor that comprises nanoparticles of at least one oxide of at least one transition metal doped with a rare earth element, obtained through a sol-gel process, as a sensitive material.

43. The method of claim 7, wherein the target compound(s) or molecules(s) are selected from the group consisting of atmospheric pollutants, explosives and precursors of explosives.

44. The method of claim 7, wherein the target compound(s) or molecules(s) are selected from peroxides.

45. The method of claim 44, comprising detecting or assaying peroxides vis--vis volatile organic compounds.

46. The method of claim 44, wherein the target compound(s) or molecules(s) are selected from the group consisting of hydrogen peroxide, hydroperoxides, and peroxides of ketones.

47. The method of claim 9, wherein the organic solvent is selected from the group consisting of C1 to C6 aliphatic alcohols, acetonitrile, tetrahydrofuran, toluene; and mixtures thereof.

48. The method of claim 11, wherein the thin film is covering at least in part one or both faces of a flat substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a graph that shows fluorescence emission spectra, realized in example 5, representing the evolution of the fluorescence emission as a function of the wavelength as it is observed for colloidal solutions of nanoparticles of EuVO.sub.4 not containing hydrogen peroxide (curve A) or variable quantities of H.sub.2O.sub.2 of 6, 12, 24, 36, 48, 60, 120, 241, 362, 1508 ppmv (curves B, C, D, E, F, G, H, I, J, K).

(2) On the abscissa is plotted the emission wavelength of the solutions (in nm), and on the ordinate is plotted the fluorescence intensity (in arbitrary units).

(3) FIG. 2 represents the absorption (FIG. 2A) and emission (FIG. 2B) spectra of a solid thin film constituted of nanoparticles of EuVO.sub.4.

(4) On the abscissa is plotted the absorption (FIG. 2A) or emission (FIG. 2B) wavelength of the thin film (in nm), and on the ordinate is plotted the transmission (in %) or the fluorescence intensity (in arbitrary units) (Example 6).

(5) FIG. 3 represents a schematic vertical sectional view of the device used for the tests for detecting vapors of H.sub.2O.sub.2. This assembly makes it possible to subject the optical sensor to an atmosphere saturated with peroxide.

(6) FIG. 4 represents the evolution of the fluorescence intensity at 617 nm, after excitation at 270 nm, as observed for an optical sensor comprising a solid thin film constituted of nanoparticles of EuVO.sub.4, when said sensor is successively exposed to ambient air then to vapors of hydrogen peroxide.

(7) On the abscissa is plotted the time (in seconds), and on the ordinate is plotted the fluorescence intensity at 617 nm (in arbitrary units).

(8) FIG. 5 represents the evolution of the fluorescence intensity at 617 nm, after excitation at 270 nm, as observed for an optical sensor comprising a solid thin film constituted of nanoparticles of EuVO.sub.4 when said sensor is exposed to ambient air or to vapors of volatile organic compounds, namely ethanol, acetone, and toluene vapors.

(9) FIG. 6 represents the evolution of the fluorescence intensity at 617 nm, after excitation at 270 nm, as observed for an optical sensor comprising a thin film constituted of nanoparticles of EuVO.sub.4 when said sensor is successively exposed to ambient air, to vapors of ethanol then to vapors of hydrogen peroxide.

(10) On the abscissa is plotted the time (in seconds), and on the ordinate is plotted the fluorescence intensity at 617 nm (in arbitrary units).

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

Examples

Example 1

(11) In this example, an aqueous sol of nanoparticles of EuVO.sub.4 (x=0 in the formula indicated above) is prepared.

(12) Firstly aqueous solutions containing the precursors of oxides are prepared, namely on the one hand a solution of europium nitrate and on the other hand a solution of sodium orthovanadate, then these solutions are mixed at 60 C.

(13) The solution of europium nitrate, the concentration of which is 0.1 M, is prepared by dissolution of 1.71 g of Eu(NO.sub.3).sub.3, 5 H.sub.2O in 40 mL of water.

(14) The solution of sodium orthovanadate, the concentration of which is 0.1 M, is prepared from 0.55 g of Na.sub.3VO.sub.4 which are poured into 30 mL of water. The pH of the solution of Na.sub.3VO.sub.4 is controlled and adjusted if necessary to a value comprised between 12.3 and 12.8 by addition of sodium hydroxide.

(15) The solution of europium nitrate is introduced into a round-bottomed two-necked flask surmounted by a condenser and a dropping funnel.

(16) The solution of sodium orthovanadate is placed in said a dropping funnel and added drop by drop to the contents of the round-bottomed two-necked flask, under magnetic stirring. After addition of all the solution of orthovanadate, the sol obtained is left to stir for 30 minutes at 60 C., during which time the reaction between europium nitrate and sodium orthovanadate takes place.

(17) After this reaction time, the sol obtained is brought back to ambient temperature then it is diluted 20 times.

(18) Then, said diluted sol is left for 30 minutes in an ultrasonic bath in order to assure good dispersion of the particles in aqueous phase.

(19) Then the diluted sol undergoes an operation of dialysis against deionized water in order to remove the salts.

(20) The water is renewed twice a day for three days.

(21) An aqueous sol of nanoparticles of EuVO.sub.4 at around pH 6 is finally obtained with a content by weight of inorganic (in other words EuVO.sub.4) of around 0.4%, which may optionally be filtered before use.

Example 2

(22) In this example, an aqueous sol of nanoparticles of Y.sub.0.5VO.sub.4Eu.sub.0.5 is prepared in the presence of sodium citrate.

(23) Firstly are prepared aqueous solutions containing the precursors of oxides, namely a solution of europium nitrate, a solution of sodium orthovanadate, and a solution of yttrium nitrate, then these solutions of precursors are mixed with a solution of sodium citrate at 60 C.

(24) The solution of europium nitrate, the concentration of which is 0.1 M, is prepared by dissolution of 0.86 g of Eu(NO.sub.3).sub.3, 5 H.sub.2O in 20 mL of water.

(25) The solution of sodium orthovanadate, the concentration of which is 0.1 M, is prepared from 0.55 g of Na.sub.3VO.sub.4 which are poured into 30 mL of water. The pH of the solution of Na.sub.3VO.sub.4 is controlled and adjusted if necessary to a value comprised between 12.3 and 12.8 by addition of sodium hydroxide.

(26) The solution of yttrium nitrate, the concentration of which is 0.1 M, is prepared from 0.77 g of Y(NO.sub.3).sub.3, 6 H.sub.2O and 20 mL of water.

(27) The solution of sodium citrate, the concentration of which is 0.1 M, is obtained by dissolution of 0.88 g of C.sub.6H.sub.5Na.sub.3O.sub.7, 2 H.sub.2O in 30 mL of water.

(28) The solutions of europium nitrate and yttrium nitrate are mixed and introduced into a round-bottomed two-necked flask surmounted by a condenser and a dropping funnel.

(29) The solution of sodium citrate is placed in this dropping funnel and is then added dropwise to the contents of the round-bottomed two-necked flask, under magnetic stirring.

(30) A white precipitate of lanthanide citrate then forms.

(31) The solution of sodium orthovanadate is placed in the dropping funnel.

(32) The white precipitate of lanthanide citrate is then completely dissolved by addition, dropwise, of the solution of sodium orthovanadate to the contents of the round-bottomed two-necked flask under magnetic stirring.

(33) After the complete addition of the different reagents, the sol is left stirring at 60 C. for 30 minutes during which time the reaction between europium nitrate, sodium orthovanadate and yttrium nitrate takes place.

(34) After this reaction time, the sol obtained is brought back to ambient temperature then it undergoes an operation of dialysis against deionized water for three days, while renewing the water twice a day in order to eliminate the salts and the excess of sodium citrate.

(35) A stable, transparent and colorless aqueous sol of nanoparticles of Y.sub.0.5VO.sub.4:Eu.sub.0.5 is then obtained at around pH 7.5 with a content by weight of inorganic (Y.sub.0.5VO.sub.4Eu.sub.0.5) of around 0.5%.

Example 3

(36) In this example, a hydro-organic sol of Y.sub.0.5VO.sub.4Eu.sub.0.5 nanoparticles is prepared.

(37) The aqueous sol of Y.sub.0.5VO.sub.4Eu.sub.0.5 nanoparticles of example 2 is placed in a semi-permeable membrane then it undergoes an operation of dialysis against a solution containing a mixture of water and acetonitrile in equal proportions.

(38) The final sol keeps the stability as well as the fluorescence properties of the aqueous sol but enables the solubilization of organic peroxides such as TATP for example.

Example 4

(39) In this example, a thin film constituted of nanoparticles of EuVO.sub.4 is prepared.

(40) In order to form a thin film of EuVO.sub.4 from the sol of example 1, it is necessary to perform a transfer of particles in an organic solvent.

(41) The solvent commonly used for the implementation of thin layers is ethanol, or an ethanol-water mixture.

(42) The sol of example 1 thus undergoes an operation of dialysis against a mixture composed of 90% of absolute ethanol and 10% of deionized water for 24 hours, whereby a hydro-alcoholic sol is obtained.

(43) The two faces of a substrate constituted of a glass slide, of microscope slide type, are coated by dip coating of the substrate in the hydro-alcoholic sol obtained above at a rate of 15 cm.Math.min.sup.1 or by spin coating at a speed of 800 rpm.

(44) A drying is carried out for 5 minutes in the open air in order to eliminate the solvents from the layer formed.

Example 5

(45) In this example, the effect of solutions of H.sub.2O.sub.2 having various concentrations on the emission spectrum of a colloidal solution of EuVO.sub.4 is studied.

(46) To observe the effect of a solution of H.sub.2O.sub.2 on the emission spectrum of a colloidal solution of EuVO.sub.4, quartz vessels containing a constant liquid volume of 2.9 mL are prepared.

(47) They contain 1.5 mL of colloidal solution, a variable quantity of hydrogen peroxide, namely 6, 12, 24, 36, 48, 60, 120, 241, 362, and 1508 ppmv of H.sub.2O.sub.2, and are made up with water.

(48) A vessel contains only 1.5 mL of colloidal solution without hydrogen peroxide.

(49) Emission spectra of the solutions: they are acquired by a Horiba Jobin Yvon Fluoromax-P spectrofluorometer.

(50) The excitation wavelength used is 270 nm. The aperture of the monochromators inlet slots is adjustable (1 to 5 nm). It is chosen as a function of the emission intensity of the solutions in order to obtain a sufficient signal, without saturating the detector. The quartz vessels are positioned in the sample holder of the spectrofluorometer.

(51) The emission spectra obtained are shown in FIG. 1.

(52) FIG. 1 clearly highlights the affinity between the sensitive material and hydrogen peroxide in solution.

Example 6

(53) In this example, the absorption (FIG. 2A) and emission (FIG. 2B) spectra are taken of a solid thin film constituted of nanoparticles of EuVO.sub.4 such as that prepared in example 4.

(54) The acquisition protocols of the absorption and emission spectra are presented below.

(55) Absorption spectra of the films: they are acquired by a Perkin Elmer Lambda 900 spectrometer.

(56) A standard scanning is used between 800 and 200 nm in transmission, with an interval between the data of 1 nm. The blank is made with air.

(57) Emission spectra of the films: they are acquired by a Horiba Jobin Yvon Fluoromax-P spectrofluorometer.

(58) The excitation wavelength used is 270 nm. The aperture of the monochromators inlet slots is adjustable (1 to 5 nm). It is chosen as a function of the emission intensity of the films in order to obtain a sufficient signal, without saturating the detector. The quartz substrate on which is deposited the film is positioned in the measuring chamber with a tilt angle of 45 with respect to the excitation incident beam.

(59) The absorption and emission spectra are shown respectively in FIGS. 2A and 2B.

(60) It should be noted that these spectra relate to EuVO.sub.4 but that the spectra are similar whatever the Eu content.

Example 7

(61) In this example, the detection of vapors of hydrogen peroxide is carried out using an optical sensor comprising a thin film constituted of nanoparticles of EuVO.sub.4.

(62) A spectrofluorometer is used in kinetic mode, which makes it possible to measure the fluorescence intensity at a given wavelength, referred to as measurement wavelength, under a given excitation wavelength, as a function of time.

(63) The excitation wavelength used is 270 nm whereas the measurement wavelength is 617 nm.

(64) As is represented in FIG. 3, a glass substrate (31), on which a film of EuVO.sub.4 (32) has been deposited beforehand as has been described in example 4, is introduced into a quartz vessel (33), which is itself positioned in the sample holder of the spectrofluorometer (Horiba Jobin Yvon FluoroMax)

(65) All of the measurements are carried out at ambient temperature and according to the protocol described previously.

(66) The kinetic measurement is started in order to check the stability of the fluorescence intensity of the film in the absence of vapors of hydrogen peroxide.

(67) After 30 minutes of exposure to UV, the quartz vessel is saturated with vapors of H.sub.2O.sub.2 by pouring 0.5 mL of a 17.5% by volume aqueous solution of H.sub.2O.sub.2 into the bottom thereof, without the solution of H.sub.2O.sub.2 (34) entering into contact with the film as is illustrated in FIG. 3.

(68) The vessel is then rapidly closed using Parafilm (35) in order to continue the kinetic measurement.

(69) The reduction in fluorescence at 617 nm due to the interaction between the film of EuVO.sub.4 and the vapors of H.sub.2O.sub.2 is then measured.

(70) FIG. 4 represents the fluorescence intensity in the absence, then in the presence, of hydrogen peroxide vapors. For the first 1800 seconds, the film of EuVO.sub.4 is not exposed to H.sub.2O.sub.2 in order to check the stability of the fluorescence intensity of the film.

(71) After 1800 seconds (time t1 in FIG. 4), the hydrogen peroxide solution is introduced into the vessel (arrow F1 on FIG. 4), which is immediately closed. The fluorescence intensity then drops considerably.

Example 8

(72) In this example, the selectivity of an optical sensor comprising a thin film constituted of nanoparticles of EuVO.sub.4 vis--vis peroxides is highlighted.

(73) A spectrofluorimeter is used in kinetic mode, which makes it possible to measure the fluorescence intensity at a given wavelength, referred to as measurement wavelength, under a given excitation wavelength, as a function of time.

(74) The excitation wavelength used is 270 nm, whereas the measurement wavelength is 617 nm.

(75) A glass substrate, on which a film of EuVO.sub.4 has been deposited previously as has been described in example 4, is introduced into a quartz vessel, which is itself positioned in the sample holder of the spectrofluorometer (Horiba Jobin Yvon FluoroMax)

(76) All of the measurements are carried out at ambient temperature and according to the protocol described previously.

(77) The kinetic measurement is started in order to check the stability of the fluorescence intensity of the film.

(78) After 10 minutes, the quartz vessel is saturated with vapors of an organic solvent by pouring 0.5 mL of the solvent into the bottom of the quartz vessel without the solvent entering into contact with the film as in example 7.

(79) The vessel is then rapidly closed using Parafilm and the kinetic measurement is continued. The evolution of the fluorescence at 617 nm of the film of EuVO.sub.4 is thus measured in the presence of an atmosphere saturated with the vapors of the solvent.

(80) Three tests are carried out each time with a different solvent, namely ethanol, acetone, then toluene.

(81) Let I.sub.0 be the fluorescence intensity at 617 nm of the film of EuVO.sub.4 at time t.sub.0, and I the fluorescence intensity of the same film at 617 nm at time t.

(82) FIG. 5 represents the evolution of I/I.sub.0 as a function of time in seconds, in the presence of a solvent (ethanol, acetone or toluene) in the bottom of the vessel or when the sensor is simply exposed to ambient air before addition of any interferent (interfering compound).

(83) The measurements in the presence of the different solvents and in ambient air were carried out separately but are reported on the same graph in order to facilitate comparison.

(84) The I/I.sub.0 ratio remains globally constant. The sensor is thus selective vis--vis peroxides and the solvents do not create any interference.

Example 9

(85) In this example, a glass substrate, on which a film of EuVO.sub.4 has been deposited beforehand as has been described in example 4, is introduced into a quartz vessel, which is itself positioned in the sample holder of the spectrofluorometer (Horiba Jobin Yvon FluoroMax).

(86) All of the measurements are carried out at ambient temperature and according to the previously described protocol.

(87) The film is firstly exposed to ambient air, up to a time t2 (300 s), at which ethanol is introduced into the vessel (arrow F2 of FIG. 6).

(88) After the exposure of the sensor to vapors of ethanol for 1800 seconds, several drops of hydrogen peroxide are introduced (arrow F3 of FIG. 6) into the vessel at time t3 (2100 s), still without the film entering into contact with the liquid.

(89) The measurement of the fluorescence intensity of the film of EuVO.sub.4 is continued and its variations are reported on FIG. 6.

(90) This figure thus represents the evolution of the I/I.sub.0 ratio as a function of time when the film is placed in the empty vessel for 300 seconds, in the presence of ethanol for 1800 seconds, then in the presence of hydrogen peroxide for 2100 seconds.

(91) FIG. 6 shows that the fluorescence intensity drops after exposure to hydrogen peroxide. This indicates that the sensor offers good sensitivity and very high specificity with regard to peroxides despite the presence of organic solvents.

Example 10

(92) In this example, the performance stability over time of an optical sensor comprising a thin film constituted of nanoparticles of EuVO.sub.4 is highlighted.

(93) In this example, a sensor identical to that of examples 4 and 7 to 9 is used.

(94) The day it is made, the sensor is exposed to vapors of hydrogen peroxide, in saturated atmosphere in the measurement vessel, for 10 minutes.

(95) The value of the fluorescence intensity is then noted I.sub.0. Said sensor is then stored for 100 days in ambient air and in daylight. A new measurement is then carried out under exposure of vapors saturated with hydrogen peroxide for 5 minutes. The fluorescence intensity is then measured.

(96) Since the values I.sub.0 and I.sub.100 are identical, of the order of (1.30.1).Math.10.sup.7, it may be concluded that the fluorescence performances of the sensor are stable over long time periods, greater than 3 months here, and without taking particular precautions with regard to the conservation conditions of said sensor unlike the usual organic materials. The fluorescence intensity at 617 nm of a film of EuVO.sub.4 excited at 270 nm is thus conserved despite storage in air and in daylight. The material thus has a lifetime greater than three months under exposure to daylight.

REFERENCES

(97) [1] S. Yao, S. Yuang, J, Xu, Y. Wang, J. Luo, S. Hu, Applied Clay Science, 33, 35, 2006 [2] (a) J. G. Hong, J. Maguhn, D. Freitag, A. Kettrup, Fresenius J. Anal. Chem., 361, 124, 1998 (b) R. Schulte-Ladbeck, P. Kolla, U. Karst, Analyst, 127, 1352, 2002 [3] D. Lu, A. Cagan, R Minoz, T. Tangkuaram, J. Wang, Analyst, 131, 1279, 2006 [4] F. Bohrer, C. Colesniuc, J. Park, I. Schuller, A. Kummel, W. Trogler, Journal of American Chemical Society, 130, 3712, 2008 [5] C. Guzman, G. Orozco, Y. Verde, S. Jimenez, L. A. Godinez, E. Juaristi, E. Bustos, Electrochimica Acta, 54, 1728, 2009 [6] D. Laine, C. Roske, F. Cheng, Anal. Chim. Acta, 608, 56, 2008 [7] R. Munoz, D. Lu, A. Cagan, J. Wang, Analyst, 132, 560, 2007 [8] A. Mills, P. Grosshans, E. Snadden, Sensors and Actuators B, 136, 458, 2009 [9] A. Apblett, B. Kiran., S. Malka, N. Materer, A. Piquette, Ceram Trans, 172, 29, 2005 [10] J. Sanchez, W. Trogler, Journal of Material Chemistry, 18, 5134, 2008 [11] M. Germain, M. Knapp, Inorganic Chemistry, 47, 9748, 2008 [12] S. Malashikhin, N. Finney, Journal of the American Society, 130, 12846, 2008 [13] X. Shu, Y. Chen, H. Yuang, S. Gao, D. Xiao, Anal. Chem., 79(10), 3695, 2007 [14] D. Casanova, C. Bouzigues, T. L. Nguyen, R. O. Ramodiharilafy, L. Bouzhir-Sima, T. Gacoin., J. P. Boilot, P. L. Tharaux, A. Alexandrou, Nature Nanotechnology, 4, 581, 2009 [15] P. Belleville, C R. Chimie, 13, 97, 2010 [16] H. Althues, P. Simon, S. Kaskel, Journal of Material Chemistry, 17, 758, 2007 [17] M. Yu, J. Lin, F. Fang, Chemistry of Materials, 17, 1783, 2005 [18] Q. Zhou, L. Zhang, H. Fan, L. Wu, Y. Lv, Sensors and Actuators B, 144, 192, 2010 [19] FR-A-2 703 791 [20] Rouqurol et al., Pure & Applied Chemistry, 66(8), 1994, pages 1739-1758 [21] Sanchez-Pedrono, Anal. Chem. Acta, 182, 285, 1986 [22] B. Valeur, Molecular Fluorescence: Principles and Applications, Ed. WILEY VCH, New York, 2002.