METHODS FOR STORING HOLOGRAPHIC DATA AND ARTICLES HAVING ENHANCED DATA STORAGE LIFETIME DERIVED THEREFROM BACKGROUND The present disclosure relates to methods for storing holographic data. Further, the present disclosure relates to holographic data storage media and articles having an enhanced data storage lifetime, which are derived from these methods. Optical data storage technology has largely evolved on the basis of surface storage phenomena. In all surface-based optical data storage systems, each bit of data occupies a specific physical location in the storage medium. The data density of the optical media, is therefore limited by physical constraints on the minimum size of a recording spot. An alternative approach to the traditional surface-based storage system is volumetric storage technology, in which the full volume of a storage medium is used to increase data capacity. The two most common techniques for volumetric storage are multi-layer and holographic. The multi-layer approach resembles the multiple-layer CD/DVD approach except that the data is written and retrieved using various optical phenomena that are sensitive to focused beams, so that various depths in the medium can be addressed by changing the depth of the focus. This technique eliminates the complexities of fabricating multiple layers and assembling them and, furthermore, removes the limitation on the number of layers, making it primarily a function of the focusing capabilities of the optical system. In holographic storage, on the other hand, data is stored throughout the volume of the medium via three-dimensional or volume interference patterns. In the holographic recording process, holograms are recorded by the superposition of two beams within the volume of a photosensitive medium. The interference pattern from the superposition of the two beams results in a change or modulation of the refractive index of the holographic medium and are known as holograms. This modulation within the medium may serve to record both the intensity and phase information of the superposed beams. Known holographic data storage techniques can be classified into page-based holographic data storage and bit-wise holographic data storage. In page-based holographic storage, data is written in "parallel", on arrays or "pages" containing anywhere from one to 1x106 or more bits. A signal beam, which contains digitally encoded data, is superposed on a reference beam within the medium, resulting in an interference pattern within the medium which in turn leads to corresponding changes in the refractive index. Each bit is generally stored as a part of the interference pattern that generates the index modulation over the volume of the holographic storage medium in a given spot, and can be thought of as consuming some small portion of the overall index modulation. The recorded intensity and phase data may then be retrieved by exposing the storage medium to the reference beam. A holographic storage medium that can support large index changes may consequently store multiple pages within the volume of the holographic medium by angular, wavelength, phase-code or related multiplexing techniques. In bit-wise holography or microholographic data storage, every bit is written as a microhologram or reflection gratings and is generated by two interfering counter-propagating focused beams. The data is retrieved by using a read beam to diffract off the microhologram to obtain a signal. The heart of any holographic storage system is the storage medium. Recently, polymer dye-doped data storage materials for holographic data storage media have been developed. However, typically after data is written, subsequent data readout may quickly lead to erasure of the written information to such materials. Therefore, there is a need for techniques to enhance the lifetime of holographic data in a photochemically active dye based holographic medium. BRIEF DESCRIPTION Disclosed herein are methods for storing holographic data in a storage medium having an enhanced data storage lifetime, and articles made using these methods. In one aspect, the present invention provides a method for storing holographic data, said method comprising: step (A) providing an optically transparent substrate comprising a photochemically active dye and a singlet-oxygen generator; step (B) irradiating the optically transparent substrate with a holographic interference pattern, wherein the pattern has a first wavelength and an intensity both sufficient to convert, within a volume element of the substrate, at least some of the photochemically active dye into a photo-product, and producing within the irradiated volume element concentration variations of the photo-product corresponding to the holographic interference pattern, thereby producing an optically readable datum corresponding to the volume element; and step (C) activating the optically transparent substrate to generate singlet oxygen to stabilize the optically readable datum. In still yet another aspect, the present invention provides an optical writing/reading method, said method comprising: step (A) irradiating with a holographic interference pattern an optically transparent substrate that comprises a photochemically active dye and a singlet-oxygen generator, wherein the pattern has a first wavelength and an intensity both sufficient to convert, within a volume element of the substrate, at least some of the photochemically active dye into a photo-product, and producing within the irradiated volume element concentration variations of the photo-product corresponding to the holographic interference pattern, thereby producing a first optically readable datum corresponding to the volume element; wherein the holographic interference pattern is produced by simultaneously irradiating the optically transparent substrate with a signal beam corresponding to data and a reference beam that does not correspond to data; step (B) activating the optically transparent substrate to generate singlet oxygen to stabilize the optically readable datum; and step (C) irradiating the optically transparent substrate with a read beam and reading the optically readable datum by detecting diffracted light. In another aspect, the invention provides a method for forming a holographic data storage article is provided, said method comprising forming a film of an optically transparent substrate comprising an optically transparent plastic material, a photochemically active dye, and a singlet-oxygen generator. In still yet another aspect, the present invention provides for a holographic data storage medium that can be used for storing data in the form of holograms. The data storage medium comprises an optically transparent plastic material, a photochemically active dye and a singlet-oxygen generator. In another embodiment, the present invention provides for a data storage medium having at least one optically readable datum stored therein. The data storage medium comprises an optically transparent plastic material, a photochemically active dye, a singlet-oxygen generator, a photo-product derived from the photochemically active dye, a photo-stable product derived from the photochemically active dye, the photo-product, or combinations thereof; wherein the at least one optically readable datum is stored as a hologram patterned within at least one volume element of the optically transparent substrate included within the data storage medium. These and other features, aspects, and advantages of the present invention may be understood more readily by reference to the following detailed description. DRAWINGS These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: FIG. 1 is a schematic representation of holographic data storage and stabilizing in one embodiment of the present invention; FIG. 2 is a schematic representation of a holographic data storage system in one embodiment of the present invention; FIG. 3 is a schematic representation of a holographic data storage system in one embodiment of the present invention; FIG. 4 is a schematic representation of a holographic data storage system in one embodiment of the present invention; FIG. 5 is a graph illustrating the variation in absorbance with wavelength of a medium including a photochemically active dye, before and after a exposure to light of a specific wavelength, in one embodiment of the present invention; FIG. 6 is a graph illustrating the variation in absorbance with wavelength of a medium including a photo-product of a photochemically active dye and a singlet oxygen sensitizer before and after exposure to light of a specific wavelength, in one embodiment of the present invention; FIG. 7 is a graph illustrating the variation in absorbance with wavelength of a medium including a photo-stable product of a photo-product of a photochemically active dye before and after exposure to light of a specific wavelength, in one embodiment of the present invention; FIG. 8 is a graph illustrating the variation in absorbance with wavelength of a medium including a photochemically active dye and a singlet oxygen sensitizer, before and after exposure to light of a specific wavelength, in one embodiment of the present invention. DETAILED DESCRIPTION Some aspects of the present invention and general scientific principles used herein can be more clearly understood by referring to U.S. Patent Application 2005/0136333 (Serial Number 10,742,461), which was published on June 23, 2005; co-pending Application having Serial Number 10/954,779, filed on September 30, 2004; and co¬pending Application having Serial Number 11/260806, filed on October 27, 2005; all of which are incorporated herein in their entirety. It should be noted that with respect to the interpretation and meaning of terms in the present application, in the event of a conflict between this application and any document incorporated herein by reference, the conflict is to be resolved in favor of the definition or interpretation provided by the present application. In the following specification and the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings. The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. As defined herein, the term "volume element" means a three dimensional portion of the total volume of an optically transparent substrate. As used herein the term "aliphatic radical" refers to an organic radical having a valence of at least one consisting of a linear or branched array of atoms that is not cyclic. Aliphatic radicals are defined to comprise at least one carbon atom. The array of atoms comprising the aliphatic radical may include heteroatoms such as nitrogen, sulfur, silicon, selenium and oxygen or may be composed exclusively of carbon and hydrogen. For convenience, the term "aliphatic radical" is defined herein to encompass, as part of the "linear or branched array of atoms which is not cyclic" a wide range of functional groups such as alkyl groups, alkenyl groups, alkynyl groups, haloalkyl groups, conjugated dienyl groups, alcohol groups, ether groups, aldehyde groups, ketone groups, carboxylic acid groups, acyl groups (for example carboxylic acid derivatives such as esters and amides), amine groups, nitro groups, and the like. For example, the 4-methylpent-l-yl radical is a C6 aliphatic radical comprising a methyl group, the methyl group being a functional group which is an alkyl group. Similarly, the 4-nitrobut-l-yl group is a C4 aliphatic radical comprising a nitro group, the nitro group being a functional group. An aliphatic radical may be a haloalkyl group which comprises one or more halogen atoms which may be the same or different. Halogen atoms include, for example; fluorine, chlorine, bromine, and iodine. Aliphatic radicals comprising one or more halogen atoms include the alkyl halides trifluoromethyl, bromodifluoromethyl, chlorodifluoromethyl, hexafluoroisopropylidene, chloromethyl, difluorovinylidene, trichloromethyl, bromodichloromethyl, bromoethyl, 2-bromotrimethylene (e.g., -CH2CHBrCH2-), and the like. Further examples of aliphatic radicals include allyl, aminocarbonyl (i.e., -CONH2), carbonyl, 2,2-dicyanoisopropylidene (i.e., -CH2C(CN)2CH2-), methyl (i.e., - CH3), methylene (i.e., -CH2-), ethyl, ethylene, formyl (i.e.,-CHO), hexyl, hexamethylene, hydroxymethyl (i.e.,-CH20H), mercaptomethyl (i.e., -CH2SH), methylthio (i.e., -SCH3), methylthiomethyl (i.e., -CH2SCH3), methoxy, methoxycarbonyl (i.e., CH3OCO-) , nitromethyl (i.e., -CH2NO2), thiocarbonyl, trimethylsilyl ( i.e., (CH3)3Si-), t-butyldimethylsilyl, 3-trimethyoxysilypropyl (i.e., (CH3O)3SiCH2CH2CH2-), vinyl, vinylidene, and the like. By way of further example, a C1 - C10 aliphatic radical contains at least one but no more than 10 carbon atoms. A methyl group (i.e., CH3-) is an example of a C1 aliphatic radical. A decyl group (i.e., CH3(CH2)cr) is an example of a C10 aliphatic radical. As used herein, the term "aiomatic radical" refers to an array of atoms having a valence of at least one comprising at least one aromatic group. The array of atoms having a valence of at least one comprising at least one aromatic group may include heteroatoms such as nitrogen, sulfur, selenium, silicon and oxygen, or may be composed exclusively of carbon and hydrogen. As used herein, the term "aromatic radical" includes but is not limited to phenyl, pyridyl, furanyl, thienyl, naphthyl, phenylene, and biphenyl radicals. As noted, the aromatic radical contains at least one aromatic group. The aromatic group is invariably a cyclic structure having 4n+2 "delocalized" electrons where "n" is an integer equal to 1 or greater, as illustrated by phenyl groups (n = 1), thienyl groups (n = 1), furanyl groups (n = 1), naphthyl groups (n = 2), azulenyl groups (n = 2), anthraceneyl groups (n = 3) and the like. The aromatic radical may also include nonaromatic components. For example, a benzyl group is an aromatic radical that comprises a phenyl ring (the aromatic group) and a methylene group (the nonaromatic component). Similarly a tetrahydronaphthyl radical is an aromatic radical comprising an aromatic group (C6H3) fused to a nonaromatic component -(CH2)4-. For convenience, the term "aromatic radical" is defined herein to encompass a wide range of functional groups such as alkyl groups, alkenyl groups, alkynyl groups, haloalkyl groups, haloaromatic groups, conjugated dienyl groups, alcohol groups, ether groups, aldehyde groups, ketone groups, carboxylic acid groups, acyl groups (for example carboxylic acid derivatives such as esters and amides), amine groups, nitro groups, and the like. For example, the 4-methylphenyl radical is a C7 aromatic radical comprising a methyl group, the methyl group being a functional group which is an alkyl group. Similarly, the 2-nitrophenyl group is a C6 aromatic radical comprising a nitro group, the nitro group being a functional group. Aromatic radicals include halogenated aromatic radicals such as 4-trifluoromethylphenyl, hexafluoroisopropylidenebis(4-phen-l-yloxy) (i.e., -OPhC(CF3)2PhO-), 4- chloromethylphen-1-yl, 3-trifluorovinyl-2-thienyl, 3-trichloromethylphen-l-yl (i.e., 3- CCl3Ph-), 4-(3-bromoprop-l-yl)phen-l-yl (i.e., 4-BrCH2CH2CH2Ph-), and the like. Further examples of aromatic radicals include 4-allyloxyphen-l-oxy, 4-aminophen-l- yl (i.e., 4-H2NPh-), 3-aminocarbonylphen-l-yl (i.e., NH2COPh-), 4-benzoylphen-l-yl, dicyanomethylidenebis(4-phen-l-yIoxy) (i.e., -OPhC(CN)2PhO-), 3-methylphen-l-yl, methyIenebis(4-phen-l-yloxy) (i.e., -OPhCH2PhO-), 2-ethylphen-l-yl, phenylethenyl, 3-formyl-2-thienyl, 2-hexyl-5-furanyl, hexamemylene-l,6-bis(4-phen-l-yloxy) (i.e., - OPh(CH2)6PhO-), 4-hydroxymethylphen-l-yl (i.e., 4-HOCH2Ph-), 4- mercaptomethylphen-1-yl (i.e., 4-HSCH2Ph-), 4-methylthiophen-l-yl (i.e., 4-CH3SPh- ), 3-methoxyphen-l-yl, 2-methoxycarbonylphen-l-yloxy (e.g., methyl salicyl), 2- nitromethylphen-1-yl (i.e., 2-NO2CH2PI1), 3-trimethylsilylphen-l-yl, 4-t- butyldimethylsilylphenl-1-yl, 4-vinylphen-l-yl, vinylidenebis(phenyl), and the like. The term "a C3 - C10 aromatic radical" includes aromatic radicals containing at least three but no more than 10 carbon atoms. The aromatic radical 1-imidazolyl (C3H2N2-) represents a C3 aromatic radical. The benzyl radical (C7H7-) represents a C7 aromatic radical. As used herein the term "cycloahphatic radical" refers to a radical having a valence of at least one, and comprising an array of atoms which is cyclic but which is not aromatic. As defined herein a "cycloahphatic radical" does not contain an aromatic group. A "cycloahphatic radical" may comprise one or more noncyclic components. For example, a cyclohexylmethyl group (C6H11CH2-) is a cycloahphatic radical which comprises a cyclohexyl ring (the array of atoms which is cyclic but which is not aromatic) and a methylene group (the noncyclic component). The cycloahphatic radical may include heteroatoms such as nitrogen, sulfur, selenium, silicon and oxygen, or may be composed exclusively of carbon and hydrogen. For convenience, the term "cycloahphatic radical" is defined herein to encompass a wide range of functional groups such as alkyl groups, alkenyl groups, alkynyl groups, haloalkyl groups, conjugated dienyl groups, alcohol groups, ether gioups, aldehyde groups, ketone groups, carboxylic acid groups, acyl groups (for example carboxylic acid derivatives such as esters and amides), amine groups, nitro groups, and the like. For example, the 4-methylcyclopent-l-yl radical is a C6 cycloaliphatic radical comprising a methyl group, the methyl group being a functional group which is an alkyl group. Similarly, the 2-nitrocyclobut-l-yl radical is a C4 cycloaliphatic radical comprising a nitro group, the nitro group being a functional group. A cycloaliphatic radical may comprise one or more halogen atoms which may be the same or different. Halogen atoms include, for example; fluorine, chlorine, bromine, and iodine. Cycloaliphatic radicals comprising one or more halogen atoms include 2-trifluoromethylcyclohex-l- yl, 4-bromodifluoromethylcyclooct-1 -yl, 2-chlorodifluoromethylcyclohex-1 -yl, hexafluoroisopropylidene-2,2-bis (cyclohex-4-yl) (i.e., -C6H10C(CF3)2 C6H10-), 2- chloromethylcyclohex-1-yl, 3- difluoromethylenecyclohex-l-yl, 4- trichloromethylcyclohex-1-yloxy, 4-bromodichloromethylcyclohex-l-ylthio, 2- bromoethylcyclopent-1-yl, 2-bromopropylcyclohex-l-yloxy (e.g., CH3CHBrCH2C6H10O-), and the like. Further examples of cycloaliphatic radicals include 4-allyioxycyclohex-l-yl, 4-aminocyclohex-l-yl (i.e., H2NC6H10-), 4- aminocarbonylcyclopent-1-yl (i.e., NH2COC5H8-), 4-acetyloxycyclohex-l-yl, 2,2- dicyanoisopropylidenebis(cyclohex-4-yloxy) (i.e., -OC6H10C(CN)2C6H10O-), 3- methylcyclohex-1-yl, methylenebis(cyclohex-4-yloxy) (i.e., -OC6HioCH2C6H100-), 1-ethylcyclobut-l-yl, cyclopropylethenyl, 3-formyl-2-terahydrofuranyI, 2-hexyl-5- tetrahydrofuranyl, hexamethylene-l,6-bis(cyclohex-4-yloxy) (i.e., -O C6H10(CH2)6C6H10O-), 4-hydroxymethylcyclohex-l-yl (i.e., 4-HOCH2C6H10-), 4- mercaptomethylcyclohex-1-yl (i.e., 4-HSCH2C6H|