Process for the preparation of fluxed up-conversion phosphors

A process for the preparation of an up-conversion phosphor of the general formula (I)

• wherein
• x = 0.0001 - 0.0500;
• z = 0.0000 or z = 0.0001 to 0.3000 with the proviso that y = x + z;
• A is selected from the group consisting of Mg, Ca, Sr, and Ba;
• B is selected from the group consisting of Li, Na, K, Rb, and Cs;
• B* is selected from the group consisting of Li, Na, and K,
• Ln1 is selected from the group consisting of praseodymium (Pr), erbium (Er),
• and neodymium (Nd);
• and
• Ln2 is gadolinium (Gd),
• the process comprising:
• providing the following components:
• i) at least one of
• a lanthanoid salt selected from the group consisting of a lanthanoid nitrate, a lanthanoid carbonate, a lanthanoid carboxylate, and a lanthanoid sulfate, and/or
• a lanthanoid oxide,
• wherein a lanthanoid ion in the lanthanoid oxide or lanthanoid salt is selected from praseodymium, gadolinium, erbium, and neodymium;
• and at least two of the lanthanoid ions for co-doping,
• ii) a silicate or a silicon dioxide,
• iii) at least one alkaline earth metal salt, and
• at least one alkali metal salt selected from a lithium salt or a lithium compound, and optionally selected from a sodium salt and potassium salt, and
• iv) at least one flux selected from the group consisting of ammonium halide, alkali metal halide, alkaline earth metal halide, and lanthanoid halide,
• a) mixing components i), ii), iii) and iv) by grinding to obtain a mixture, or
• b) mixing components i), ii), iii) and iv) in an organic polar or nonpolar solvent that is not a protic solvent by grinding to obtain a mixture;
• c) precalcining the mixture from b) at 600 to 1000° C., to remove an organic component, for at least 1 h, under air atmosphere to obtain a precalcined mixture, and optionally cooling to room temperature;
• and
• d) calcining the mixture from a) or the precalcined mixture from c) at a temperature from 600 to < 1000° C., for at least 3 h, and
• e) obtaining a silicate-based up-conversion phosphor of the general formula (I), wherein at least 3.5% by weight of the at least one flux is used, based on a total amount of reactants.