The embodiments provide a fluorescent rare earth complex having strong emission intensity and excellent durability, and also provide a security medium using the complex. The rare earth complex according to the embodiment comprises a rare earth ion, a diphosphine dioxide ligand and a β-diketone ligand wherein two phosphorus atoms contained in the diphosphine dioxide ligand individually have substituents different from each other.

Disclosed is a rare earth complex including: one or a plurality of rare earth ions; and a ligand forming a coordinate bond with the rare earth ions. At least a part of the rare earth ions are at least one kind selected from the group consisting of lutetium(III) ions, yttrium(III) ions, and gadolinium(III) ions. The ligand includes a residue obtained by removing one or more hydrogen atoms from a fluorescent condensed polycyclic aromatic compound.

Disclosed is a rare earth complex having a rare earth ion and a phosphine oxide ligand that is coordinated with the rare earth ion and is represented by the following formula (I):

##STR00001## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, and R.sup.6 each independently represent an alkyl group which may have a substituent.

A compound according to Formula (I), or a pharmaceutically acceptable salt thereof:

##STR00001##

wherein R.sup.1 and R.sup.2 are each independently selected from optionally substituted C.sub.1-6-alkyl and optionally substituted aryl; R.sup.3, R.sup.4, R.sup.5, and R.sup.6 are each independently selected from the group consisting of H, halo, optionally substituted C.sub.1-6-alkyl, and optionally substituted C.sub.1-6 alkoxy; and R.sup.7 is a phosphorus containing moiety, wherein a phosphorus atom is bonded to Au.

The embodiments provide a fluorescent rare earth complex having strong emission intensity and excellent durability, and also provide a security medium using the complex. The rare earth complex according to the embodiment comprises a rare earth ion, a diphosphine dioxide ligand and a β-diketone ligand wherein two phosphorus atoms contained in the diphosphine dioxide ligand individually have substituents different from each other.

[Problem] To provide: fluorescent particles that are used to create a fluorescent material for coating an object in the vicinity of a fluid, that move regularly in the fluid while suppressing halation generated by the objects, and that enable the motion/movement of the fluid to be sharply visualized; an inspection device; and an inspection method.

[Solution] Substantially spherical fluorescent particles comprising a mixture containing at least one fluorescent material and a synthetic resin, wherein: the fluorescent material is excited by any purple visible light and UV rays having a wave-length of 290-405 nm, and emits visible light having a peak wavelength within the range of 410-620 nm; and the fluorescent particles have diameters of 100 nm to 1 mm and are distinguishable from bubbles and/or foreign bodies in the fluid when irradiated with the light.

A rare earth compound including: one or a plurality of rare earth ions; and a ligand coordinated with the rare earth ion and having a condensed polycyclic aromatic group. At least part of the rare earth ions is a terbium(III) ion. The condensed polycyclic aromatic group is a residue formed by removing a hydrogen atom bonded to a condensed aromatic ring in formula (1) below from a condensed polycyclic aromatic compound represented by the following formula (1). Also disclosed is a luminescent body including the rare earth compound.

##STR00001##

A phosphine oxide group-contained transition metal complex represented by chemical formula (1), and a polymer, a mixture, a composition, and an organic electronic device.

A phosphine oxide compound represented by the following formula (I) and a rare earth complex containing the same are disclosed:

##STR00001## wherein n represents an integer of 3 or more, Ar.sup.1 represents an n-valent aromatic group, L represents a divalent linker group, and Ar.sup.2 and Ar.sup.3 each independently represent a monovalent aromatic groups.

The embodiments provide a fluorescent rare earth complex having strong emission intensity and excellent durability, and also provide a security medium using the complex. The rare earth complex according to the embodiment comprises a rare earth ion, a diphosphine dioxide ligand and a -diketone ligand wherein two phosphorus atoms contained in the diphosphine dioxide ligand individually have substituents different from each other.