NOVELTY - A photoluminescent compound comprising metal of the series of lanthanides and neutral ligands, or a mixture of the compounds, is new.    USE - The photoluminescent compound is useful for preparing spectrum converter, and solar device (all claimed) for exploiting solar energy.    ADVANTAGE - Both the photoluminescent compound and the mixture of photoluminescent compounds can be advantageously used in the construction of spectrum converters capable of enhancing the performances of solar devices (i.e. devices for exploiting solar energy) such as, for example, photovoltaic cells, and photoelectrolytic cells. Additionally, the compound and the mixture of compounds have an optimized intrinsic quantum efficiency of lanthanide with respect to the ligands coordinated with the metal and to the group or groups of substituents present in the ligands, and are capable of increasing the number of photons effectively convertible to radiations which can be used by a solar device.    DETAILED DESCRIPTION - A photoluminescent compound comprising Ln(A)x(L1) (L2) or a mixture of compounds comprising Ln(A)x(L1)(L2), is new.    Ln=represents a metal of the series of lanthanides;    (A)=represents a mono-anionic ligand selected from beta -diketonates having general formula (II), carboxylates having general formula (III), alcoholates having general formula (IV), amides having general formula (V), carbamates having general formula (VI), ketophosphonates having general formula (VII);    R1, R3 and R4=equal to or different from each other, are selected from linear or branched 1-20C alkyl groups, optionally containing heteroatoms, aryl groups optionally substituted, heteroaryl groups optionally substituted, cycloalkyl groups optionally substituted, heterocyclic groups optionally substituted;    R2=represents a hydrogen atom; or a halogen atom such as fluorine, chlorine, bromine; or it is selected from linear or branched 1-20C alkyl groups, optionally containing heteroatoms, aryl groups optionally substituted, heteroaryl groups ally substituted, heterocyclic groups optionally substituted; or R2 can be optionally bound to R1 so as to form a cycle containing from 3 to 12 carbon atoms, saturated, unsaturated, or aromatic, optionally substituted with linear or branched 1-20C alkyl groups, optionally containing heteroatoms, aryl groups optionally substituted, heteroaryl groups optionally substituted, cycloalkyl groups optionally substituted, heterocyclic groups optionally substituted; the cycle optionally containing heteroatoms such as oxygen, sulfur, nitrogen, silicon, phosphorus, selenium;    x=2 or 3;    L1 and L2=equal to or different from each other, represent neutral ligands selected from phosphine oxides having general formula (VIII), phosphates having general formula (IX), phenanthrolines having general formula (X), ketones having general formula (XI), and neutral polydentate ligands selected from compounds having general formula (XII) or (XIII); and    R5, R6, R7, and R8=equal to or different from each other, represent a hydrogen atom; or they are selected from linear or branched 1-20C alkyl groups, optionally containing heteroatoms, aryl groups optionally substituted, heteroaryl groups optionally substituted, cycloalkyl groups optionally substituted, heterocyclic groups optionally substituted.    Provided that at least one of R1-R8 represents a benzodithiophene group having general formula (XIV), (XV), (XVI) or (XVII).    R9-R16=equal to or different from each other, represent a hydrogen atom; or they are selected from linear or branched 1-20C alkyl groups, optionally containing heteroatoms, aryl groups optionally substituted, heteroaryl groups optionally substituted, cycloalkyl groups optionally substituted, heterocyclic groups optionally substituted.    INDEPENDENT CLAIMS are:    (1) a mono-anionic ligand selected from compounds having general formula (II), (III), (IV), (V), (VI) or (VII);    (2) a neutral ligand L1 or L2 selected from compounds having general formula (VIII), (IX), (X), (XI), (XII) or (XIII);    (3) a spectrum converter comprising at least one compound having general formula (I), or at least a mixture of compounds having general formula (I); and    (4) a solar device comprising a spectrum converter comprising at least one compound having general formula (I), or at least a mixture of compounds having general formula (I).