An ink composition comprising: a rare-earth complex containing one kind of trivalent rare-earth ion selected from the group consisting of Eu 3+, Tb 3+, Sm 3+, Er 3+, Pr 3+, Ho 3+, Tm 3+ and Dy 3+, and a phosphine oxide ligand represented by the following general formula and coordinated to the rare-earth ion, and a light-emitting material different from the rare-earth complex, wherein an absolute value of a difference between a wavelength (λ1) at which a light emission intensity of the rare-earth complex is maximum and a wavelength (λ2) at which a light emission intensity of the light-emitting material is maximum, is 50 nm or more, wherein the phosphine oxide ligand is a bidentate ligand, wherein the rare-earth complex is a rare-earth complex polymer and contains a linked structure formed by coordinating the phosphine oxide ligand to two of the rare-earth ions, and wherein the rare-earth complex further contains a ligand represented by the following general formula and a ligand represented by the following general formula: in the general formula, Ar 1 and Ar 2 are each independently an aromatic group optionally containing a substituent group; Ar 3 is a divalent group represented by the following general formula, or; and n is 1 or 2: in the general formulae to, R 1 is each independently a monovalent substituent group; X is a sulfur atom or an oxygen atom; R 2 is a hydrogen atom or a hydrocarbon group; m is an integer of from 0 to a number of substitutable sites of a ring to which R 1 is bound; and when there are a plurality of R 1 s, they are optionally the same or different, and in the general formula, E is a phosphine oxide group represented by the following general formula: in the general formula, Ar 4 and Ar 5 are each independently an aromatic group optionally containing a substituent group; Ar 1 and Ar 4 are optionally bound to each other directly or via a linking group; and Ar 2 and Ar 5 are optionally bound to each other directly or via a linking group, and in the general formulae and, Q 11 and Q 12 are each independently an aliphatic hydrocarbon group optionally containing a substituent group; Q 21 is an aliphatic hydrocarbon group optionally containing a substituent group; Q 22 is an aromatic hydrocarbon group optionally containing a substituent group or an aromatic heterocyclic group optionally containing a substituent group; and Z is a hydrogen atom or a deuterium atom. a rare-earth complex containing one kind of trivalent rare-earth ion selected from the group consisting of Eu 3+, Tb 3+, Sm 3+, Er 3+, Pr 3+, Ho 3+, Tm 3+ and Dy 3+, and a phosphine oxide ligand represented by the following general formula and coordinated to the rare-earth ion, and a light-emitting material different from the rare-earth complex, wherein an absolute value of a difference between a wavelength (λ1) at which a light emission intensity of the rare-earth complex is maximum and a wavelength (λ2) at which a light emission intensity of the light-emitting material is maximum, is 50 nm or more, wherein the phosphine oxide ligand is a bidentate ligand, wherein the rare-earth complex is a rare-earth complex polymer and contains a linked structure formed by coordinating the phosphine oxide ligand to two of the rare-earth ions, and wherein the rare-earth complex further contains a ligand represented by the following general formula and a ligand represented by the following general formula: in the general formula, Ar 1 and Ar 2 are each independently an aromatic group optionally containing a substituent group; Ar 3 is a divalent group represented by the following general formula, or; and n is 1 or 2: in the general formulae to, R 1 is each independently a monovalent substituent group; X is a sulfur atom or an oxygen atom; R 2 is a hydrogen atom or a hydrocarbon group; m is an integer of from 0 to a number of substitutable sites of a ring to which R 1 is bound; and when there are a plurality of R 1 s, they are optionally the same or different, and in the general formula, E is a phosphine oxide group represented by the following general formula: in the general formula, Ar 4 and Ar 5 are each independently an aromatic group optionally containing a substituent group; Ar 1 and Ar 4 are optionally bound to each other directly or via a linking group; and Ar 2 and Ar 5 are optionally bound to each other directly or via a linking group, and in the general formulae and, Q 11 and Q 12 are each independently an aliphatic hydrocarbon group optionally containing a substituent group; Q 21 is an aliphatic hydrocarbon group optionally containing a substituent group; Q 22 is an aromatic hydrocarbon group optionally containing a substituent group or an aromatic heterocyclic group optionally containing a substituent group; and Z is a hydrogen atom or a deuterium atom.