Rare-earth complex and uses thereof

A rare-earth complex represented by the following general formula (I):

• wherein
• Ln is Eu or Sm, and
• R1 is the following general formula (i):
• where B6 and B7 are each independently an alkylene group or alkynylene group, each of which having a straight chain or a branched chain and which may contain at least one atom selected from the group consisting of O and N, or alternatively, —O—, and
• A10 and A11 are each independently an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a heterocyclic group,
• (a) wherein when Ln is Eu, at least one of R2, R3, R4, and R5 is a C1 - C20 alkyl group, a C2 - C20 alkenyl group, or a C2 - C20 alkynyl group, having a branched chain;
• (b) wherein when Ln is Sm, R2, R3, R4, and R5 each independently being an alkyl group, alkenyl group or alkynyl group each having a straight chain or a branched chain, or alternatively an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a heterocyclic group;
• X1 and X2 each independently being perhalogenated alkyl groups,
• Y being hydrogen, heavy hydrogen, a halogen group, a hydroxyl group, a sulfonic group, a carbonyl group, a nitro group, a cyano group, an amino group, an alkyl group having a straight chain or a branched chain, or alternatively, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, a heterocyclic group, or a group made of a straight chain or a branched chain including no hydrogen atom, and
• n being 1 or 2;
• m being 2, 3, or 4.