Process for the preparation of up-conversion phosphors
A process can be used for the preparation of an up-conversion phosphor of the general formula (I): A 1-x-y-z B* y B 2 SiO 4 :Ln 1 x ,Ln 2 z , (I). The process involves preparing a mixture, introducing the mixture into a reaction chamber of a thermal apparatus, heating the mixture until a thermal treatment temperature is reached with a heating ramp, thermally treating the heated mixture for a holding time of at least 0.02 h, cooling the thermally treated material to room temperature while maintaining a cooling ramp, and obtaining a silicate-based lanthanoid ion-doped phosphor according to formula (I).
1 . A process for the preparation of an up-conversion phosphor of the general formula (I)
A 1-x-y-z B* y B 2 SiO 4 :Ln 1 x ,Ln 2 z , (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;
Ln 1 is selected from the group consisting of praseodymium (Pr), erbium (Er), and neodymium (Nd); and
Ln 2 is gadolinium (Gd),
the process comprising:
preparing a mixture with:
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 combinations thereof; and/or
a lanthanoid oxide,
wherein a lanthanoid ion in the lanthanoid oxide or lanthanoid salt is selected from the group consisting of praseodymium, gadolinium, erbium, and neodymium and combinations thereof,
ii) a silicate or a silicon dioxide,
iii) at least one alkaline earth metal salt, and
at least one alkali metal salt including a lithium salt and/or a lithium compound, and optionally further including a sodium salt and/or a potassium salt, and
optionally
iv) at least one flux selected from the group consisting of ammonium halide, alkali metal halide, alkaline earth metal halide, and lanthanoid halide,
introducing the mixture into a reaction chamber of a thermal apparatus,
heating the mixture until a thermal treatment temperature is reached of from 600° C. to <1000° C., with a heating ramp of from 10° C./h-400° C./h, to obtain a heated mixture,
thermally treating the heated mixture at a temperature of from 600° C. to <1000° C., with a holding time of at least 0.02 h, to obtain a thermally treated material,
cooling the thermally treated material to room temperature while maintaining a cooling ramp of from 10° C./h-400° C./h, and
obtaining a silicate-based lanthanoid ion-doped phosphor according to the general formula (I).
2 . The process according to claim 1 , wherein the mixture is prepared without solvent.
3 . The process according to claim 1 , wherein the mixture is ground and/or compacted before being introduced into the reaction chamber.
4 . The process according to claim 1 , wherein the mixture comprises at least 0.01%-10.0% by weight of the at least one flux.
5 . The process according to claim 4 , wherein the mixture comprises 1.5%-4.0% by weight of the at least one flux.
6 . The process according to claim 1 , wherein the thermal treatment is conducted batchwise or continuously.
7 . The process according to claim 1 , wherein the thermal apparatus is a batchwise furnace or a continuous furnace.
8 . The process according to claim 7 , wherein the thermal apparatus is a muffle furnace, air circulation furnace, chamber furnace, trolley hearth furnace, fluidized-bed furnace, push-through furnace, flow-through furnace, rotary tube furnace, drum furnace, tunnel furnace, vertical furnace, or paternoster furnace.
9 . The process according to claim 1 , wherein when the thermal apparatus is a rotary tube furnace or a drum furnace, a working tube or drum is heated before introducing the mixture.
10 . The process according to claim 1 , wherein the thermal treatment is conducted under air atmosphere.
11 . The process according to claim 1 , wherein when the mixture comprises more than 1.0% by weight of said lanthanoid ion, prior to the cooling of the thermally treated material, a further thermal treatment is conducted under a reducing atmosphere at a temperature of from 600° C. to <1000° C., with a holding time of at least 0.02 h.
12 . The process according to claim 11 , wherein the reducing atmosphere is a CO-containing atmosphere or a forming gas.
13 . The process according to claim 1 , wherein the lanthanoid ion is praseodymium.
14 . The process according to claim 1 , wherein alkali metals of the at least one alkali metal salt are sodium and/or lithium.
15 . The process according to claim 1 , wherein an alkaline earth metal of the at least one alkaline earth metal salt is calcium.
16 . The process according to claim 1 , wherein the silicate-based lanthanoid ion-doped phosphor according to the general formula (I) is doped with praseodymium.
17 . The process according to claim 1 , wherein the silicate-based lanthanoid ion-doped phosphor according to the general formula (I) is ground.
18 . The process according to claim 1 , wherein the lanthanoid oxide is Pr 6 O 11 and/or Gd 2 O 3 .
19 . The process according to claim 1 , wherein the at least one alkaline earth metal salt is calcium carbonate, and the at least one alkali metal salt is lithium carbonate and sodium carbonate.
20 . The process according to claim 1 , wherein the mixture comprises the at least one flux, and the at least one flux is selected from the group consisting of ammonium chloride, sodium chloride, sodium fluoride, sodium bromide, lithium fluoride, lithium chloride, calcium chloride, calcium fluoride, praseodymium fluoride, and praseodymium chloride.