Abstract: An optical information recording medium includes a substrate formed in a concave-convex state by providing pits or grooves corresponding to recorded information, used for optically reproducing the information by irradiation of a light beam, and may also include a recording layer. The optical information recording medium includes a temperature responsive layer 21 whose reflectance and/or transmittance for the light beam changes with an increase in temperature caused by the irradiation of a light beam and a light absorption layer 22. With such an arrangement, the present invention provides an optical information recording medium enabling secure and highly accurate readout of information recorded with high density, a recording method and a readout method using the same, a readout device, and a recording device.

Abstract: Optical information media containing a metal material layer and a carbon material layer are disclosed. The layering of the metal material layer and the carbon material layer are designed to reduce or eliminate problems associated with oxidation and berm formation during writing of data to the media.

Abstract: One embodiment of an optical medium includes a substrate, a data recording layer positioned on the substrate, a selectively transmissive layer positioned on the data recording layer, and a label recording layer positioned on the selectively transmissive layer, the label recording layer optically accessible at only certain wavelengths through the data recording layer and through the selectively transmissive layer.

Abstract: The present invention provides a thin film for a reflection film or for a semi-transparent reflection film, which has at least one silver compound phase of nitride, oxide, complex oxide, nitroxide, carbide, sulfide, chloride, silicide, fluoride, boride, hydride, phosphide, selenide and telluride of silver, dispersed in a matrix formed of silver. The thin film according to the present invention keeps its reflectance without significant loss even after a long period of use, and can prolong the life of various devices which comprises the thin film as a reflection film, such as an optical recording medium and a display. The thin film can be also applied to a semi-reflective/semi-transparent film used in the optical recording medium.

Abstract: A thin film for a reflection film or a semi-transparent reflection film, which has a compound phase comprising at least one selected from the group consisting of a nitride, an oxide, a complex oxide, a nitroxide, a carbide, a sulfide, a chloride, a silicide, a fluoride, a boride, a hydride, a phosphide, a selenide and a telluride of gallium, palladium or copper, dispersed in a matrix formed of silver or a silver alloy. The compound phase in the thin film may include at least one compound selected from the group consisting of nitride, oxide, complex oxide, nitroxide, carbide, sulfide, chloride, silicide, fluoride, boride, hydride, phosphide, selenide and telluride of silver. The thin film of the present invention minimizes the deterioration of the reflectance even after a long period of use, and can prolong the life of various devices which use the thin film as a reflection film, such as an optical recording medium and a display.

Abstract: A phase-change recording material used for an information recording medium utilizing a crystalline state as a non-recorded state and an amorphous state as a recorded state, which has the composition of the following formula (1) as the main component: (Sb1?xSnx)1?y?w?zGeyTewM1z??formula (1) wherein each of x, y, z and w represents atomicity, x, z and w are numbers which satisfy 0.01?x?0.5, 0?z?0.3 and 0?w?0.1, respectively, and the element M1 is at least one element selected from the group consisting of In, Ga, Pt, Pd, Ag, rare earth elements, Se, N, O, C, Zn, Si, Al, Bi, Ta, W, Nb and V, and (I) when z=0 and w=0, y is a number which satisfies 0.1?y?0.3, (II) when 0?z?0.3 and w=0, y is a number which satisfies 0.05?y?0.3, and (III) when 0?z?0.3 and 0<w?0.1, y is a number which satisfies 0.01?y?0.3.

Abstract: Disclosed herein is a super resolution optical disc. The super resolution optical disc comprises dielectric layers, and a mask layer formed between the dielectric layers, in which the mask layer is constructed as a complex mask layer comprising a metallic oxide (MOx) or metallic nitride (MNy), and a metallic thin film formed thereon. A size of the cavities and an amount of metallic particles in cavities created by illumination of recording laser can be controlled to increase a level of a reproduction signal for recording marks and to enhance the quality of the reproduction signal.

Abstract: The optical information recording medium of the present invention includes a plurality of information layers provided on a substrate and an optical separating layer provided between information layer adjacent to each other, and information is recorded or reproduced by irradiation of a laser beam. When an information layer that is provided closest to a laser beam incident side of the plurality of information layers is taken as a first information layer and an optical separating layer provided in contact with the first information layer is taken as a first optical separating layer, then the first information layer comprises a recording layer, a transmittance adjusting layer that adjusts a transmittance of the first information layer, and a low refractive index layer provided between the transmittance adjusting layer and the first optical separating layer.

Abstract: An optical information recording medium, recording/reproducing method thereof, and recording/reproducing apparatus with superior signal quality for high-density recording that has high storage reliability is provided. The optical information recording medium of the present invention has at least one information layer having a recording layer and a dielectric layer in order on a transparent substrate. The dielectric layer is comprised of greater than or equal to 50 molecule percent and less than or equal to 98 molecule percent of Zn—O, and greater than or equal to 2 molecule percent to less than or equal to 50 molecule percent of one or more compounds selected from the group consisting of Y—O, Ce—O, Nb—O, Ta—O, Cr—O and Mo—O.

Abstract: The present invention provides a phase change non-volatile memory material comprising a base material and at least one non-metallic light element selected from the group consisting of boron, carbon, nitrogen and oxygen, wherein the base material has a composition which corresponds to either that of congruent melting of the type with a minimum melting point or that of eutectic melting within the range of ±0.15 atomic fraction for each constituent element, thereby having a melting temperature of 600° C. or lower. The phase change non-volatile memory material according to the present invention may be utilized to reduce the electric power needed for reset/set operation and thermal interference between memory cells.

Abstract: An information recording medium of the present invention includes a recording layer whose phase changes by irradiation with a laser beam or application of current. The recording layer contains, as its main component, a composite composed of Ge and Sb that are essential components, and Te that is an optional component. The composite has a composition within a region enclosed by: point (a) (35, 65, 0), point (b) (36.9, 60, 3.1), point (c) (3.2, 60, 36.8), and point (d) (5, 95, 0) in terms of a coordinate (Ge, Sb, Te)=(x, y, z) on the triangular coordinate shown in FIG. 1, where point (b) corresponds to a point at Sb=60 on Ge60Te40—Ge35Sb65, point (c) corresponds to a point at Sb=60 on Te—Ge5Sb95, and the region includes lines extending between point (a) and point (b), point (b) and point (c), point (c) and point (d), and point (d) and point (a).

Abstract: An optical disc having a transition linear velocity of 8-11 m/s when irradiating continuous light with 11±1 mW and a wavelength of 660±10 nm using a pickup head with a numerical aperture (NA) of 0.65, and satisfying the following condition: ?R=|Rb?Ra|?3% where Rb is a reflectance of an unrecorded area, and Ra is a reflectance of the top of an eye pattern after ten cycles of recording. In one recording mode therefor, the disc is rotated at a constant angular velocity so as to have a linear velocity of 3-4 m/s on an innermost track and a linear velocity of 8-9 m/s on an outermost track. In another mode, the disc is rotated at a constant angular velocity so as to have a linear velocity of 5-6 m/s on an innermost track and a linear velocity of 13-14 m/s on an outermost track.

Abstract: An object of the invention is to write-once record and reproduce, or only reproduce, a mark smaller than the resolution limit; obtain a high level of reproduction performance (CNR and the like); and realize a high level of reproduction durability. In the invention, between a signal reproducing functional layer composed of Sb or Te and a protecting layer there is introduced a thermally stable diffusion preventing layer, and thereby reactions between the signal reproducing functional layer and the protecting layer due to increased temperature can be prevented or suppressed while increasing reproduction durability.

Abstract: An optical information recording medium 1 is constructed by sequentially layering a reflective layer 11, a protective layer 12, a recording layer 13, a protective layer 14, and a light transmissive protective layer 15 on a substrate 10. As the recording layer 13, a recording layer containing ZnS, SiO2, and Sb as principal components, or preferably, a recording layer expressed by a compositional formula [(ZnS)x(SiO2)1-x]y(SbzX1-z)1-y (where 0<x?1.0, 0.3?y?0.7, and 0.8<z?1.0 are met and X denotes at least one element selected from a group of Ga, Te, V, Si, Zn, Ta, and Tb) is adopted.

Abstract: An optical information recording medium that can simultaneously achieve both a high transmittance and high signal quality of an information layer, improve the reliability of long-term conservation, and reduce the manufacturing cost, and a manufacturing method thereof are provided. To achieve this, according to the present invention, in an optical information recording medium comprising at least one information layer on a substrate, at least one of the information layers has a recording layer and a dielectric layer, the recording layer contains Te, O, and M (M is one or a plurality of elements selected from Au, Pd, and Pt) as major components, the dielectric layer has a thermal conductivity of 0.01 W/K·cm or more, and the dielectric layer has an extinction coefficient of 0 through 1.0 inclusive.

Abstract: A write-once information recording medium having a high recording sensitivity and reliability with respect to long-term storage is provided. The information recording medium has a recording layer on a substrate, to which information can be recorded and from which information can be reproduced by irradiating the recording layer with laser light or applying electrical energy to the recording layer. The recording layer contains, as its primary components, TeO2 and a material A, where the material A is a material that exhibits a eutectic reaction with TeO2.

Abstract: The object of the present invention is to provide a multilayer phase-change information recording medium comprises a substrate, and N layers of information layer (N represents an integral number of 2 or more), and each of the information layers comprises at least a recording layer in which information is recorded by irradiating laser beam to induce a phase change between crystalline phase and amorphous phase. The present invention is characterized in that when the information layer is disposed so that a first information layer, a second information layer, a third information layer . . .

Abstract: A method for mass-producing a recording mark capable of being reproduced even below the diffraction limit in the information recording medium. A medium comprising: a substrate including a first material on the surface, and a second material formed on a first area on the substrate, and a third material at least whose surface energy or surface curvature are different from the second material, and the second material and third material possess at least different chemical or physical characteristics, and at least the surface energy or surface curvature of the third material are greater than the second material, moreover a region formed of the third material contains less than 20 percent of the second material, and the second or the third material can be melted for performing recording or reproduction, so that a recording mark can be produced that is capable of being read even below the diffraction limit in the information recording medium.

Abstract: An information recording medium, 15 capable of recording information by irradiation of light or applying electrical energy, wherein at least one of first and second dielectric layers 102, 106, first interface layer and counter-incident side interface layer 103, 105 is formed from a Si—In—Zr/Hf—O-based material containing at least Si, In, M1 (M1 represents at least one element selected from among Zr and Hf) and oxygen (O), with Si content being 1 atomic % or more. This medium has high recording sensitivity when information is recorded thereon, high overwrite cycle-ability and high signal intensity.

Abstract: The optical recording medium comprises an active layer of inorganic material, able to undergo deformations due to the effect of an optical radiation, presenting a front face designed to receive an optical radiation during writing operations and a rear face. An additional metal layer is arranged on the rear face of the active layer. The additional metal layer preferably has a thickness comprised between 9 nanometers and 12 nanometers. The inorganic material of the active layer can be a tellurium and zinc alloy comprising an atomic percentage of between 60% and 70% of zinc and between 30% and 40% of tellurium, and preferably 65% of zinc and 35% of tellurium. The medium can comprise a semi-reflecting layer arranged on the front face of the active layer and/or a protective layer made of polymer material on the rear face.

Abstract: Optical information-recording media comprise a first transparent substrate through which a laser beam enters, a first information-recording layer deposited on the first transparent substrate, a first reflection film formed on the first information-recording layer, an intermediate layer deposited on the first reflection film, a second information-recording layer formed on the intermediate layer, a second reflection film deposited on the second information-recording layer, and a second substrate provided on the second reflection film. The recording film of each of the first and second information-recording layers has a main composition represented by (GeTe)xSb2?yInyTe3, and its composition ratio is within ranges of 0.04?y<2 and 4?x?8.

Abstract: An optical data storage medium comprises at least one active layer of inorganic material, that is able to undergo local deformations during write operations. The active layer presents a front face which is designed to receive an optical radiation at least during read operations. The support also comprises a thin tin and tellurium based alloy layer forming a semi-reflective layer disposed on the front face of the active layer.

Abstract: Disclosed is a multi-layer super resolution optical disc. In the multi-layer super resolution optical disc, at least two recording layers, each of which comprises at least two mask layers and impact absorption layers formed between the mask layers, are laminated, and intermediate layers of polymer thermo-set by ultraviolet rays are formed between the recording layers. Accordingly, jitter characteristics for recording marks are improved, and recording density is enhanced.

Abstract: The optical recording medium is an optical recording medium having at least one information layer including a recording film, characterized in that the recording film is formed by a phase change material including at least Sb, Ge and Mg as main components.

Abstract: An exemplary dual-layered optical disc includes a transparent cover layer, a first recording layer, a space layer, a second recording layer, a reflective film, and a substrate, all of which are deposited one upon the other in this order. The first recording layer includes a re-recordable material. The second record layer includes a write-once material. Therefore, the dual-layered optical disc supplies two different types of recording layers.

Abstract: An inexpensive optical recording medium is provided that can ensure recording and reproduction of data even in case of using blue or blue-violet laser light as irradiation light and can be stored for a long time. The optical recording medium includes a recording layer. The recording layer includes a recording portion and a covering portion covering at least one side of the recording portion in a thickness direction of the recording portion. The recording portion and the covering portion are substantially formed from a plurality of types of common constituent elements. Composition ratios of the constituent elements are different between the recording portion and the covering portion.

Abstract: A Phase-change optical recording media includes a recording film that causes reversible phase-change between a crystalline phase and an amorphous phase on irradiation with light, and an interface film formed in contact with at least one surface of the recording film and containing Hf (hafnium), O (oxygen) and N (nitrogen).

Abstract: An optical recording medium has a substrate, and a recording film whose status is changed by irradiating with a laser beam. The recording film includes (?Te)x?Te3 as a major component (x is a positive real number). The ? is selected from the group consisting of Ge1-aSna and Ge1-aPba (a is a real number not less than 0 and not more than 1). The ? is selected from the group consisting of Sb2-yIny, Sb2-y-zInyBiz and Bi2-yIny (y and z are real numbers more than 0 and less than 2; y+z is more than 0 and less than 2).

Abstract: An optical information recording medium comprising a substrate, recording layer and reflecting layer, characterized in that a layer containing a mixture of carbide and oxide is disposed over a surface of the reflecting layer which faces to the recording layer. The carbide is a carbide of at least one metal selected from Ti, Zr, V, Nb, Ta, Cr, Mo and W, and the oxide is an oxide of at least one metal selected from Ti, Zr, V, Nb, Ta, Cr, Mo and W.

Abstract: To provide a sputtering target used for the formation of a recording layer of a recordable optical recording medium, wherein the sputtering target contains Bi and Fe and the packing density of the sputtering target is greater than 96%, and a recordable optical recording medium manufactured by using the sputtering target, which the recordable optical recording medium is capable of high-density recording even in the blue laser's wavelength range.

Abstract: An optical information recording medium includes the first to the n-th information layers (where n is an integer not less than 3) arranged in this order from a laser beam incident side. Each information layer includes a recording layer containing Te, O and M, where M denotes at least one element selected from the group consisting of Al, Si, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Ru, Rh, Pd, Ag, In, Sn, Sb, Hf, Ta, W, Re, Os, Ir, Pt, Au and Bi. Concentrations of oxygen atoms contained in the first to the n-th recording layers, namely C(1) to C(n?1), satisfy the following relationships: C(1)?C(2)? . . . ?C(n?2)?C(n?1), and C(1)?C(n?1). When two information layers are included, the oxygen atom concentration of the first information layer is made larger than that of the second information layer.

Abstract: An optical recording medium including: a substrate having translucency; a first protective layer thereon; a recording layer composed of a phase-change material; a second protective layer; and a reflective layer, wherein laser beam irradiation causes phase-change of the recording layer between a crystalline phase and an amorphous phase thereby at least one of to rewrite and to record information, wherein the phase-change material comprises Ga, Sb and Sn, Ga content, Sb content, and Sn content satisfy the following formula, and the total content of Ga, Sb and Sn is at least 80 atomic % of the entire phase-change material: Ga?Sb?Sn?(where, ?+?+?=100 atomic %), where 20??2.75?+0.708?+1.18??7.56?43, and ?/(?+?)?0.12.

Abstract: An optical recording medium includes an information layer having a recording film. The recording film contains Sb of 79 atomic % to 95 atomic % and Ge of 5 atomic % to 21 atomic % as main components, and is formed of a phase change material which does not contain the elements in the sixteenth group of the periodic table.

Abstract: A phase change optical recording medium includes at least a supporting substrate and a recording layer essentially consisting of AgInSbTe alloy compositions implementing recording and readout steps utilizing changes in reflectivity. The recording medium is characterized by the relation v0?0.7 vWH, where the critical relative velocity of phase change, v0, defined by the value of v, at which the differential coefficient, ?dR(v)/dv, reaches a maximum, when the recording medium moves against an optical unit during the recording steps at a relative velocity, v, ranging from minimum and maximum relative velocities warranted for the recording medium, vWL and vWH, respectively. When the reflectivity is measured with varying erase power PE at the linear relative scanning velocity v0, the reflectivity of the recording layer as a function of erase power, R(PE), preferably has a minimum. The recording layer has an activation energy of deterioration equal to or greater than 1.

Abstract: A write once optical recording medium has an inorganic recording film which includes an oxide film having germanium oxide (GeO) as a principal component, and a metal film adjacent to the oxide film, the metal film having a titanium/silicon alloy (TiSi) as a principal component. According to this arrangement, it is possible to construct an inexpensive write once optical recording medium with large strength capable of high density recording by using a short wavelength light source and an optical system with a high numerical aperture having excellent characteristics.

Abstract: A two-layered optical recording medium which includes a first substrate, a first information layer, a second information layer, and a second substrate formed in this order as viewed from the light beam irradiation side, the first information layer includes a first lower dielectric layer, a first recording layer, a first upper dielectric layer, a first reflective layer, and an inorganic dielectric layer formed in this order as viewed from the light beam irradiation side; the second information layer includes a second lower dielectric layer, a second recording layer, a second upper dielectric layer, and a second reflective layer formed in this order as viewed from the light beam irradiation side; and the first reflective layer is made of Cu with a content of 99.8% by mass to 95.0% by mass and one or more metals selected from Ta, Nb, Zr, Ni, Cr, Ge, Au, and Mo.

Abstract: A phase change recording medium comprising an as-deposited first recording layer configured to undergo a reversible phase change between an amorphous state and a crystalline state due to light irradiation and thereby change an optical characteristic. The as-deposited first recording layer includes a plurality of fine nuclei having an average size of 0.5 nm to 4 nm in the amorphous state.

Abstract: An information recording medium of the present invention includes a substrate and an information layer arranged on the substrate. The information layer includes a recording layer that is changed in phase reversibly between a crystalline phase and an amorphous phase by at least one of optical means and electrical means, and at least one crystalline nucleation layer that contains at least one element selected from Bi and Te and at least one element (M1) selected from Sc, Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, and Lu and is provided in contact with the recording layer.

Abstract: A super-resolution information storage medium having recording marks or pits that are smaller than the resolution limit of a beam incident from an information recording and/or reproducing apparatus, and the information recording and/or reproducing apparatus. The information storage medium includes a substrate and at least one super-resolution reproduction layer containing a super-resolution material and a high melting point material with a melting point higher than that of the super-resolution material formed on the substrate. The high melting point material suppresses movement of the super-resolution material in a melted phase so as to prevent signal degradation caused by repeated reproduction.

Abstract: An information-recording medium includes first and second recording layers each of which is formed of a phase-change material containing Bi, Ge, and Te, wherein the first recording layer is arranged nearer to a light-incident side of the laser beam than the second recording layer; a composition of Bi, Ge, and Te contained in the second recording layer is within a composition range surrounded by composition points B2, C2, D2, D6, C6, and B6 on a triangular composition diagram of Bi, Ge, and Te; and a difference (???) between a composition ? of Bi in the first recording layer and a composition ? of Bi in the second recording layer is ?1.0 to 3.0 at. %. Thus, there is provided a two-layered information-recording medium with high recording-data reliability and excellent repeated-data recording durability.

Abstract: A multilayer phase change information recording medium including plural information layers containing at least a first information layer and a last information layer, each of which includes a recording layer in which information is recorded utilizing a phase change between a crystalline phase and an amorphous phase. At least one of the plural information layers other than the last information layer includes a first lower protective layer, a first recording layer located overlying the lower protective layer, a first upper protective layer located overlying the first recording layer, a first reflective layer located overlying the first upper protective layer, and a heat diffusion layer located overlying the first reflective layer and which mainly contains In, Zn and O.

Abstract: It is an object of the present invention to provide a phase-change information recording medium, and the like, which is easy to perform initial crystallization, exhibits good recording sensitivity at a linear velocity as high as 10 double speeds or more with as much capacity as DVD-ROM, is capable of overwrite recording and has good storage reliability. For this purpose, the phase-change information recording medium comprises a substrate and at least a first protective layer, a phase-change recording layer, a second protective layer, and a reflective layer disposed on the substrate in one of this sequence and reverse sequence wherein the phase-change recording layer comprises a composition expressed by Sn?Sb?Ga?Ge?Te??X? (In this regard, X represents at lease one element selected from Ag, Zn, In and Cu. ?, ?, ?, ?, ? and ? represent composition ratio (atomic percent) of each element and are expressed as 5???25, 40???91, 2???20, 2???20, 0???10, 0???10 and ?+?+?+?+?+?=100).

Abstract: A recording medium has at least a recording layer on a transparent substrate. The recording layer has at least a first phase-changeable film and a second phase-changeable film in that order, starting on the side closest to the transparent substrate. The first phase-changeable film and the second phase-changeable film each contains at least 10 atom % and no more than 50 atom % germanium and at least 45 atom % and no more than 60 atom % tellurium. Also at least one of the phase-changeable films contains bismuth.

Abstract: A write once optical recording medium includes a substrate on which an oxide film serving as an inorganic recording film is formed, the oxide film being made of a recording material of an oxide Ge1Ox (x is an atomic number ratio) of germanium (Ge) and a composition of Ge1Ox of the oxide film being specified so as to satisfy 1.0<x<2.0.

Abstract: A phase-change recording film with stable crystallization rate and a composite target for producing the film are composed of 10 to 50 atomic percent of phase-change material containing Te or Sb and 50 to 90 atomic percent of dielectric material. Another target for producing the film is composed of dielectric material and a phase-change material containing Te or Sb attached to the dielectric material. A co-sputtering process for producing the film uses a target made of dielectric material and a target made of phase-change material containing Te or Sb to co-sputter. Because the crystallization rate of the phase-change recording film does not change as the thickness of phase-change recording film varies, manufacturing the phase-change recording film does not require to be precisely controlled unduly.

Abstract: A phase-change optical recording medium is disclosed including a supporting substrate and the following contiguous layers formed on the supporting substrate in the order recited such as a first dielectric layer, a recording layer, a second dielectric layer, a metal/alloy layer, and an ultraviolet light curing resinous layer. The recording layer is characterized by its uppermost recrystallization linear velocity ranging from about 5.0 m/sec to about 10.0 m/sec, which can be utilized in read/write/erase operations for the recording medium at linear velocities higher than the quad-speed as well.

Abstract: Phase-change compounds, and optical storage recording media, for recording and/or storage of data, comprising such compounds, according to the formula XSbySz; wherein X is selected from the group consisting of K, Rb, Tl, Na, Li, Cs and mixtures thereof; and wherein y is about 1 or about 5, and z is about 1 or about B. Preferably, X is K, y is 5 and z is B. Also provided are optical recording media comprising a layer of the phase-change material and methods of creating a reversible phasechange by irradiating the material with a laser radiation.

Abstract: An information recording medium is provided that has high recording sensitivity for recording information and superior repeated rewriting performance. The information recording medium has at least a recording layer that is changeable between a crystalline phase and an amorphous phase by applying a laser beam or electric current and a dielectric layer. The dielectric layer contains at least C, Si, Sn and O. Alternatively, the information recording medium includes at least two information layers with at least one of the information layer including at least a recording layer that is changeable between a crystalline phase and an amorphous phase by applying a laser beam or electric current and a dielectric layer. The dielectric layer contains at least C, Si, Sn and O.

Abstract: Metal alloy thin films are provided for use in the highly reflective and semi-reflective layers of optical discs. Alloys include silver alloyed with gold, palladium, copper, rhodium, ruthenium, osmium, iridium, and platinum. Other alloys include copper alloys with silver, magnesium, cadmium, aluminum, nickel, beryllium, zirconium and zinc. These alloys have moderate to high reflectivity and reasonable corrosion resistance in the ambient environment.

Abstract: An optical recording medium is provided, which are capable of recording and reproducing data with reliability even when blue or blue violet laser light is used as irradiation light. The optical recording medium includes a substrate, and a recording layer formed over the substrate and having its optical characteristic changed by irradiation of the laser light. The recording layer is substantially composed of Bi and O, and the ratio of the number of the O atoms to the total number of Bi and O atoms in the recording layer is 63-73%.