A lighting device includes a light source and a photoconversion layer including a perovskite compound represented by Formula 1. The perovskite compound absorbs at least part of light emitted from the light source and emits light having a different wavelength range from the absorbed light:

[A][B][X].sub.3  <Formula 1>

In Formula 1, A is at least one monovalent organic cation, at least one a monovalent inorganic cation, or any combination thereof, B is at least one divalent inorganic cation, and X is at least one monovalent anion.

A perovskite compound represented by Formula 1, a thin layer including the perovskite compound, and an optoelectronic device including the perovskite compound:

[A][B.sup.1.sub.nB.sup.2.sub.(1-n)][X].sub.3.  Formula 1

In Formula 1, A may be at least one selected from a monovalent organic cation, monovalent inorganic cation, and combinations thereof; B.sup.1 may be a thulium (II) (Tm.sup.2+) ion; B.sup.2 may be at least one divalent inorganic cation, where B.sup.2 is free of (e.g., does not include) Tm.sup.2+; n may be a real number that satisfies 0<n≦1; and X may be at least one monovalent anion.

The invention provides luminescent lanthanide nanoparticles having simultaneously an improved brightness and an increased lifetime of the excited-state. These nanoparticles comprise terbium ions and ions of a second lanthanide, preferentially europium, and are coated with molecules of chromophore ligand bonded to the surface of the nanoparticle. The ligand is an organic molecule comprising at least one chromophore radical of formula (I) or of formula (II): wherein R is selected from H, CN group or COOH group. The phosphorescence excited-state lifetime is improved by energy transfer from surface terbium ions to core ions of the second lanthanide The nanoparticle may further comprise a carrier molecule of analytical interest covalently attached to at least one ligand molecule.

##STR00001##

A nanocomposite includes: a matrix phase; and a functional area disposed in the matrix phase. The functional area contains monocrystal fine particles.

A lighting device includes a light source and a photoconversion layer including a perovskite compound represented by Formula 1. The perovskite compound absorbs at least part of light emitted from the light source and emits light having a different wavelength range from the absorbed light:
[A][B][X].sub.3<Formula 1>
In Formula 1, A is at least one monovalent organic cation, at least one a monovalent inorganic cation, or any combination thereof, B is at least one divalent inorganic cation, and X is at least one monovalent anion.

A nanocomposite includes: a matrix phase; and a functional area disposed in the matrix phase. The functional area contains monocrystal fine particles.

A process for treating a luminescent halogen-containing material includes contacting the luminescent halogen-containing material with an atmosphere comprising a halogen-containing oxidizing agent for a period of at least about two hours. The luminescent halogen-containing material has a composition other than (i) A.sub.x[MF.sub.y]:Mn.sup.4+, where A is Li, Na, K, Rb, Cs, or a combination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; x is the absolute value of the charge of the [MF.sub.y] ion; and y is 5, 6 or 7; (ii) Zn.sub.2[MF.sub.7]:Mn.sup.4+, where M is selected from Al, Ga, In, and combinations thereof; (iii) E[MF.sub.6]:Mn.sup.4+, where E is selected from Mg, Ca, Sr, Ba, Zn, and combinations thereof; and where M is selected from Ge, Si, Sn, Ti, Zr, and combinations thereof; or (iv) Ba.sub.0.65Zr.sub.0.35F.sub.2.70:Mn.sup.4+.

A process for treating a luminescent halogen-containing material includes contacting the luminescent halogen-containing material with an atmosphere comprising a halogen-containing oxidizing agent for a period of at least about two hours. The luminescent halogen-containing material has a composition other than (i) A.sub.x[MF.sub.y]:Mn.sup.4+, where A is Li, Na, K, Rb, Cs, or a combination thereof; M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof; x is the absolute value of the charge of the [MF.sub.y] ion; and y is 5, 6 or 7; (ii) Zn.sub.2[MF.sub.7]:Mn.sup.4+, where M is selected from Al, Ga, In, and combinations thereof; (iii) E[MF.sub.6]:Mn.sup.4+, where E is selected from Mg, Ca, Sr, Ba, Zn, and combinations thereof; and where M is selected from Ge, Si, Sn, Ti, Zr, and combinations thereof; or (iv) Ba.sub.0.65Zr.sub.0.35F.sub.2.70:Mn.sup.4+

The invention provides luminescent lanthanide nanoparticles having simultaneously an improved brightness and an increased lifetime of the excited-state. These nanoparticles comprise terbium ions and ions of a second lanthanide, preferentially europium, and are coated with molecules of chromophore ligand bonded to the surface of the nanoparticle. The ligand is an organic molecule comprising at least one chromophore radical of formula (I) or of formula (II): wherein R is selected from H, CN group or COOH group. The phosphorescence excited-state lifetime is improved by energy transfer from surface terbium ions to core ions of the second lanthanide. The nanoparticle may further comprise a carrier molecule of analytical interest covalently attached to at least one ligand molecule. ##STR00001##

CaF.sub.2 translucent ceramics includes at least two rare earth elements selected from a group consisting of La, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu.