Blue to UV Up-Converter Comprising Lanthanide Ions such as Pr3+ Activated and optionally Gd3+ Co-Activated Silicates and its Application for Surface Disinfection Purposes

Abstract

A silicate-based lanthanide ion doped material converts electromagnetic radiation energy of a longer wavelength of below 530 nm to electromagnetic radiation energy of shorter wavelengths in the range of 220 to 425 nm. The silicate-based material is a crystalline silicate material doped with lanthanide ions selected from praseodymium, gadolinium, erbium, and neodymium. For co-doping, at least two of the lanthanide ions are used. The silicate-based material is obtainable from a blend comprising salts and an organic solvent, followed by specific calcination processes and tribological impacts to adjust particle size and to increase the crystallinity of the particles. The silicate-based material can be used to inactivate microorganisms or cells covering a surface containing the silicate-based material under exposure of electromagnetic radiation energy of a longer wavelength of below 500 nm.

Claims

1: A silicate-based material, comprising: a crystalline silicate material doped with at least one lanthanide ion selected from the group consisting of praseodymium, gadolinium, erbium, and neodymium, and wherein the crystalline silicate material converts electromagnetic radiation energy of at least one longer wavelength in a range of 530 nm and below to electromagnetic radiation energy of at least one shorter wavelength in a range of 220 to 425 nm, wherein the at least one longer wavelength has a longer wavelength than the at least one shorter wavelength.

2: The silicate-based material according to claim 1, wherein the crystalline silicate material is selected from the group consisting of a cyclosilicate, a pyrosilicate, and an inosilicate.

3: The silicate-based material according to claim 1, wherein the crystalline silicate material is not a hydrate of a silicate.

4: The silicate-based material according to claim 1, wherein a crystallinity of the silicate-based material is greater than 70%.

5: The silicate-based material according to claim 1, wherein the crystalline silicate material comprises: a crystalline pure phase, or a silica-based material comprising at least one crystal phase that encompasses at least 90 weight-% of the silica-based material.

6: The silicate-based material according to claim 1, wherein the crystalline silicate material has the general formula I
A.sub.1-x-y-zB*.sub.yB.sub.2SiO.sub.4:Ln.sup.1.sub.x,Ln.sup.2.sub.z.  I wherein x=0.0001-0.05, z=0 or z=0.0001 to 0.3, and y=x+z, wherein A is selected from the group consisting of Mg, Ca, Sr, and Ba, wherein B is selected from the group consisting of Li, Na, K, Rb, and Cs, wherein B* is selected from the group consisting of Li, Na, and K, and wherein Ln.sup.1 is selected from the group consisting of praseodymium (Pr), erbium (Er), and neodymium (Nd), and Ln.sup.2, if present, is gadolinium (Gd).

7: The silicate-based material according to claim 1, wherein the crystalline silicate material is doped with the praseodymium.

8: The silicate-based material according to claim 1, wherein the crystalline silicate material is doped with the praseodymium and co-doped with the gadolinium.

9: The silicate-based material according to claim 1, wherein the crystalline silicate material is a solid solution of a crystalline silicate or of crystalline silicate doped with lanthanide ions comprising at least one alkali ion and at least one earth alkali ion.

10: The silicate-based material according to claim 1, wherein the crystalline silicate material has the general formula Ia
A.sub.1-x-y-zB*.sub.yB.sub.2SiO.sub.4:Pr.sub.x,Gd.sub.z.  Ia wherein A=Mg, Ca, Sr, or Ba, and B=Li, Na, K, Rb, or Cs, and wherein in formula Ia, x=0.0001-0.05, z=0 or z=0.0001 to 0.3, and y=x+z, wherein B* is selected from the group consisting of Li, Na, and K.

11: The silicate-based material according to claim 1, wherein the crystalline silicate material has the general formula II
(Ca.sub.1-aSr.sub.a).sub.1-2bLn.sub.bNa.sub.bLi.sub.2SiO.sub.4  II wherein a=0.0001 to 1, b=0.0001 to 1, and Ln=the at least one lanthanide ion selected from the group consisting of praseodymium, gadolinium, erbium, and neodymium.

12: The silicate-based material according to claim 1, wherein electromagnetic radiation energy of the at least one longer wavelength is in a range of 500 nm and below, and is converted to electromagnetic radiation energy of shorter wavelengths in a range of 230 nm to 380 nm.

13: The silicate-based material according to claim 11, wherein the crystalline silicate material according to formula II possesses XRPD signals in a range of 23° 2Θ to 27° 2Θ and of 34° 2Θ to 39.5° 2Θ.

14: A process for the production of a silicate-based material, the process comprising: combining the following components i), ii), and iii), i) at least one lanthanide salt and/or lanthanide oxide, wherein a lanthanide ion in the at least one lanthanide salt and/or lanthanide oxide is selected from the group consisting of praseodymium, gadolinium, erbium, and neodymium, ii) a silicate, and iii) at least one earth alkali salt and at least one alkali salt selected from the group consisting of a lithium salt, a lithium compound, a sodium salt, and a potassium salt, wherein the combining comprises: a) blending i), ii), and iii) by milling, and obtaining a mixture, or b) blending i), ii), and iii) in an organic polar or non-polar solvent that is not a protic solvent, and obtaining a mixture, wherein the obtained mixture of b) is calcinated at 600° C. to 1000° C. to remove organic components, and to obtain a calcinated mixture, performing a calcination of the mixture of a) or the calcinated mixture of b) in a calcination at a temperature below a melting temperature of the silicate-based material, wherein at least partial crystallization occurs, and performing a further calcination under a reducing atmosphere, wherein the lanthanide ion is reduced to an Ln.sup.3+ ion, and obtaining the silicate-based material.

15: The process according to claim 14, wherein the obtained silicate-based material is milled.

16: The process according to claim 15, wherein the obtained silicate-based material is subjected to tribological impacts at 100 to 500 rotations/min for 1 to 6 hours, using corundum as milling material.

17: A silicate-based material, obtainable according to the process of claim 14, wherein the silicate-based material is a crystalline silicate material doped with the at least one lanthanide ion selected from the group consisting of praseodymium, gadolinium, erbium, and neodymium, and wherein the silicate-based material is a solid solution of a crystalline silicate or crystalline silicates comprising at least one alkali ion and at least one earth alkali ion, and wherein a crystallinity of the silicate-based material is greater than 80%, and optionally, wherein the silicate-based material converts electromagnetic radiation energy of the at least one longer wavelength in a range of 530 nm and below to electromagnetic radiation energy of at least one shorter wavelength in a range of 220 to 400 nm, wherein the at least one longer wavelength has a longer wavelength than the at least one shorter wavelength.

18: A composition, foil or film, comprising the silicate-based material according to claim 1 for self-disinfection purposes or for reduction of microorganisms.

19: A method, comprising: adding the silicate-based material according to claim 1 into a coating composition or a material to provide a coaling or surface that is able to inactivate microorganisms covering the coating or surface under exposure of electromagnetic radiation energy of a longer wavelength in a range of 500 nm and below.

20: The silicate-based material according to claim 12, wherein an emission maximum of the electromagnetic radiation energy of the shorter wavelengths has an intensity of at least 1.Math.10.sup.3 counts/(mm.sup.2*s).

Description

EMBODIMENTS

[0114] Measurement Techniques

[0115] The X-ray diffractograms were recorded by using a Panalytical X'Pert PRO MPD diffractometer working in Bragg-Brentano geometry using Cu-Kα radiation and a line-scan CCD sensor. The integration time amounted to 20 s with a step size of 0.017°.

[0116] Emission spectra were recorded on an Edinburgh Instruments FLS920 spectrometer equipped with a 488 nm continuous-wave OBIS Laser by Coherent and a Peltier cooled (−20° C.) single-photon counting photomultiplier (Hamamatsu R2658P). Filters were used to suppress excitation by second order reflexes caused by the monochromators.

[0117] Milling is performed in a planetary ball mill (PM 200, Retsch), beaker/jar: corundum and grinding balls (Al2O3), 50 ml (9 balls, sample ca. 4.5 g) or 125 ml (24 balls, sample ca. 20 g) for 4 hours at 200 rotation/min after cooling of the final calcination step. Reducing atmosphere (H.sub.2/Inert gas, in particular H.sub.2/N.sub.2, preferred (H.sub.2 (5%)/N.sub.2 (95%)).

[0118] Powder Sample Synthesis

Example 1: Ca.SUB.0.98.Pr.SUB.0.01.Na.SUB.0.01 .Li.SUB.2.SiO.SUB.4

[0119] 3.3349 g (33.3200 mmol) CaCO.sub.3, 3.0588 g (34.0000 mmol) Li.sub.2SiO.sub.3, 0.1479 g (0.3400 mmol) Pr(NO.sub.3).sub.3.6H.sub.2O and 0.0180 g (0.1700 mmol) Na.sub.2CO.sub.3 were blended in hexane in an agate mortar. Na.sub.2CO.sub.3 was used for charge compensation of Ca.sup.2+/Pr.sup.3+. This precursor blend was calcined at 700° C. for two hours in air to remove organic residues. Subsequent calcination at 850° C. for 12 h in air was carried out to obtain the product phase. A final calcination step at 850° C. for six hours in reducing atmosphere is necessary to reduce Pr.sup.4+ to Pr.sup.3+.

Example 2: Ca.SUB.0.96.Pr.SUB.0.01 .Gd.SUB.0.01 .Na.SUB.0.02.Li.SUB.2.SiO.SUB.4

[0120] 3.2668 g (32.6400 mmol) CaCO.sub.3, 3.0588 g (34.0000 mmol) Li.sub.2SiO.sub.3, 0.1479 g (0.3400 mmol) Pr(NO.sub.3).sub.3.6H.sub.2O, 0.0616 g (0.1700 mmol) Gd.sub.2O.sub.3 and 0.0360 g (0.3400 mmol) Na.sub.2CO.sub.3 were blended in hexane in an agate mortar. Na.sub.2CO.sub.3 was used for charge compensation of Ca.sup.2+/Pr.sup.3+. This precursor blend was calcined at 700° C. for two hours in air to remove organic residues. Subsequent calcination at 850° C. for 12 h in air was carried out to obtain the product phase. A final calcination step at 850° C. for six hours in reducing atmosphere is necessary to reduce Pr.sup.4+ to Pr.sup.3+.

Example 3: Sr.SUB.0.98.Pr.SUB.0.01.Na.SUB.0.01.Li.SUB.2.SiO.SUB.4

[0121] 3.6169 g (24.5000 mmol) SrCO.sub.3, 2.2491 g (25.0000 mmol) Li.sub.2SiO.sub.3, 0.1088 g (0.2500 mmol) Pr(NO.sub.3).sub.3.6H.sub.2O and 0.0132 g (0.1250 mmol) Na.sub.2CO.sub.3 were blended in hexane in an agate mortar. Na.sub.2CO.sub.3 was used for charge compensation of Ca.sup.2+/Pr.sup.3+. This precursor blend was calcined at 700° C. for two hours in air to remove organic residues. Subsequent calcination at 850° C. for 12 h in air was carried out to obtain the product phase. A final calcination step at 850° C. for six hours in reducing atmosphere is necessary to reduce Pr.sup.4+ to Pr.sup.3+.

Example 4: Sr.SUB.0.96.Pr.SUB.0.01.Gd.SUB.0.01.Na.SUB.0.02.Li.SUB.2.SiO.SUB.4

[0122] 4.8186 g (32.6400 mmol) SrCO.sub.3, 3.0588 g (34.0000 mmol) Li.sub.2SiO.sub.3, 0.1479 g (0.3400 mmol) Pr(NO.sub.3).sub.3.6H.sub.2O, 0.0616 g (0.1700 mmol) Gd.sub.2O.sub.3 and 0.0360 g (0.3400 mmol) Na.sub.2CO.sub.3 were blended in hexane in an agate mortar. Na.sub.2CO.sub.3 was used for charge compensation of Ca.sup.2+/Pr.sup.3+. This precursor blend was calcined at 700° C. for two hours in air to remove organic residues. Subsequent calcination at 850° C. for 12 h in air was carried out to obtain the product phase. A final calcination step at 850° C. for six hours in reducing atmosphere is necessary to completely reduce Pr.sup.4+ to Pr.sup.3+.

Comparative Example 1

[0123] As comparative example other lanthanide doped silicate systems disclosed in the below mentioned publication were produced and measured under same conditions (Visible-to-UVC up-conversion efficiency and mechanisms of Lu.sub.7O.sub.6F.sub.9:Pr.sup.3+ and Y.sub.2SiO.sub.5:Pr.sup.3+ ceramics, Cates, Ezra L.; Wilkinson, Angus P.; Kim, Jae-Hong, Journal of Luminescence 160 (2015) 202-209; Abstract: Visible-to-UVC up-conversion (UC) by Pr.sup.3+-doped materials is a promising candidate for application to sustainable disinfection technologies, including light-activated antimicrobial surfaces and solar water treatment. In this work, we studied Pr.sup.3+ up-conversion in an oxyfluoride host system for the first time, employing Lu.sub.7O.sub.6F.sub.9:Pr.sup.3+ ceramics. Compared to the previously studied Y.sub.2SiO.sub.5:Pr.sup.3+ reference material, the oxyfluoride host resulted in a 5-fold increase in intermediate state lifetime, likely due to a lower maximum phonon energy; however, only a 60% gain in UC intensity was observed. To explain this discrepancy, luminescence spectral distribution and decay kinetics were studied in both phosphor systems. The Pr.sup.3+4f5d band energy distribution in each phosphor was found to play a key role by allowing or disallowing the occurrence of a previously unexplored UC mechanism, which had a significant impact on overall efficiency.

[0124] Lu.sub.7O.sub.6F.sub.9:Pr.sup.3+: Could not be obtained under disclosed temperature and a synthesis under increased temperature and a pressure of 350 MPa was not able due to the availability of a temperable press.

[0125] Y.sub.2SiO.sub.5:Pr.sup.3+ was as synthesized according to the publication as a pure phase.

Comparative Example 2

[0126] As a further comparative example, a lanthanide doped silicate is produced under the conditions disclosed in the US 2013/0052079 regarding the calcination temperature:

[0127] 3.3349 g (33.3200 mmol) CaCO.sub.3, 2.5123 g (34.0000 mmol) Li.sub.2CO.sub.3, 0.1479 g (0.3400 mmol) Pr(NO.sub.3).sub.3.6H.sub.2O and 0.0180 g (0.1700 mmol) Na.sub.2CO.sub.3 were blended in hexane in an agate mortar. Na.sub.2CO.sub.3 was used for charge compensation of Ca.sup.2+/Pr.sup.3+. This precursor blend was calcined at 700° C. for two hours in air to remove organic residues. Subsequent calcination at 1100° C. (and temperatures above) for 12 h in air yields in an amorphous and glassy product, which stuck at the crucible. It was not possible to separate the amorphous product from the Al.sub.2O.sub.3 crucible.

[0128] Grinding Attempts

[0129] The planetary ball mill PM 200 from Retsch was used also used for the following grinding. The inner wall of the grinding bowls and the grinding balls are made of corundum (Al.sub.2O.sub.3). Two different grinding bowls were used: 50 and 125 ml. Depending on the size, nine or 24 grinding balls were used. Depending on their size, the bowls were also filled with 4.5 g or 20 g sample. The speed of the grinding bowls is 200 rpm. The grinding time is 4 hours. Operating principle: The grinding bowls are arranged eccentrically on the sun wheel of the planetary ball mill. The rotational movement of the sun wheel is counter-rotating to that of the grinding bowl in the ratio 1:−2. The grinding balls in the grinding bowl are influenced by superimposed rotational movements, so-called Coriolis forces. The speed differences between balls and grinding bowls lead to an interaction of friction and impact forces, releasing high dynamic energies. The interaction of these forces causes the high and very effective degree of comminution of the planetary ball mills.

[0130] First an XRD of the untreated educts (CaCO.sub.3, Li.sub.2CO.sub.3, Pr.sub.6O.sub.11, Na.sub.2CO.sub.3 and SiO.sub.2) was recorded, FIG. 27a. The educt mixture was then treated in the above-mentioned planetary ball mill (200 rpm for 4 hours, FIG. 27b: XRPD). The powder diffraction pattern indicates that the target phase does not exist (FIG. 27b). Thus it can be stated that the energy input during grinding is not sufficient to synthesize the target phase. The exact value of the energy input cannot be calculated.

[0131] The powder was then sintered in air at 850° C. for 12 hours:

[0132] After this step, the reactant mixture has reacted to the target phase. The most intense reflex at 2Θ=37.39.sup.0 has an intensity of 13357 counts (FIG. 27c).

[0133] After this sintering step, the powder shows a brown body colour, since Pr.sup.4+ is present in addition to Pr.sup.3+. The latter must be reduced with a second sintering step (6 hours at 850° C.) under forming gas (H.sub.2 (5%)/N.sub.2 (95%)).

[0134] After this step, see FIG. 27d, the most intense reflex has an intensity of 15423 counts. The crystallinity can therefore be increased with this sintering step. A renewed grinding leads, see FIG. 27e, to a decrease of the crystallinity. The number of counts of the reflex is reduced to 13576.

[0135] In a second series of experiments CaLi.sub.2SiO.sub.4:Pr,Na was presented using conventional synthesis. For this purpose, the starting materials were mixed with acetone in an agate mortar and then sintered in air at 850° C. for 12 hours. The second sintering step was then carried out under forming gas (FIG. 28a: XRPD). The most intensive reflex has an intensity of 10964 counts. Then the powder sample was ground as described above:

[0136] After grinding, in particular for 4 h at 200 rpm, see FIG. 28b, the intensity of the observed reflex rose to 18665 counts. Consequently, the crystallinity can be significantly increased by subsequent grinding. In addition, it can be observed that various foreign phase reflexes also disappear during grinding.

[0137] A previous grinding of the educts does not lead to a higher crystallinity of the target phase than the subsequent grinding. In addition, foreign phase reflexes can still be observed after the sintering steps if the starting materials have been ground before sintering.

DESCRIPTION OF FIGURES

[0138] FIG. 1a: X-ray powder diffraction (XRPD) of synthesized Y.sub.2SiO.sub.5 upper XRPD and calculated XRPD of Y.sub.2SiO.sub.5.

[0139] FIG. 1b: Emission spectrum of Y.sub.2SiO.sub.5:Pr.sup.3+ upon excitation at 445 nm (75 mW) and 488 nm (150 mW) by Lasers.

[0140] FIG. 2: Emission spectrum of Ca.sub.0.98Pr.sub.0.01 Na.sub.0.01Li.sub.2SiO.sub.4 upon excitation at 445 nm (75 mW) and 488 nm (150 mW) by Lasers.

[0141] FIG. 3: X-ray diffraction pattern of Ca.sub.0.98Pr.sub.0.01 Na.sub.0.01Li.sub.2SiO.sub.4 for Cu—K.sub.α radiation (Example 1).

[0142] FIG. 4: X-ray diffraction pattern of Ca.sub.0.96Pr.sub.0.01Gd.sub.0.01Na.sub.0.02Li.sub.2SiO.sub.4 for Cu—K.sub.α radiation (Example 2).

[0143] FIG. 5: X-ray diffraction pattern of Sr.sub.0.98Pr.sub.0.01 Na.sub.0.01Li.sub.2SiO.sub.4 for Cu—K.sub.α radiation (Example 3).

[0144] FIG. 6: X-ray diffraction pattern of Sr.sub.0.96Pr.sub.0.01Gd.sub.0.01Na.sub.0.02Li.sub.2SiO.sub.4 for Cu—K.sub.α radiation (Example 4).

[0145] FIG. 7: Emission spectrum of Ca.sub.0.98Pr.sub.0.01 Na.sub.0.01Li.sub.2SiO.sub.4 upon excitation at 160 nm (Example 1).

[0146] FIG. 8: Emission spectrum of Ca.sub.0.96Pr.sub.0.01Gd.sub.0.01Na.sub.0.02Li.sub.2SiO.sub.4 upon excitation at 160 nm (Example 2).

[0147] FIG. 9: Emission spectrum of Sr.sub.0.98Pr.sub.0.01 Na.sub.0.01Li.sub.2SiO.sub.4 upon excitation at 160 nm (Example 3).

[0148] FIG. 10: Emission spectrum of Sr.sub.0.96Pr.sub.0.01Gd.sub.0.01Na.sub.0.02Li.sub.2SiO.sub.4 upon excitation at 160 nm (Example 4).

[0149] FIG. 11: Emission spectrum of Ca.sub.0.98Pr.sub.0.01Na.sub.0.01Li.sub.2SiO.sub.4 upon excitation at 445 nm (75 mW) and 488 nm (150 mW) by Lasers (Example 1).

[0150] FIG. 12: Emission spectrum of Ca.sub.0.96Pr.sub.0.01Gd.sub.0.01Na.sub.0.02Li.sub.2SiO.sub.4 upon excitation at 445 nm (75 mW) and 488 nm (150 mW) by Lasers (Example 2).

[0151] FIG. 13: Emission spectrum of Sr.sub.0.98Pr.sub.0.01 Na.sub.0.01Li.sub.2SiO.sub.4 upon excitation at 445 nm (75 mW) and 488 nm (150 mW) by Lasers (Example 3).

[0152] FIG. 14: Emission spectrum of Sr.sub.0.96Pr.sub.0.01Gd.sub.0.01Na.sub.0.02Li.sub.2SiO.sub.4 upon excitation at 445 nm (75 mW) and 488 nm (150 mW) by Lasers (Example 4).

[0153] FIG. 15: Reflection spectrum of Ca.sub.0.98Pr.sub.0.01 Na.sub.0.01Li.sub.2SiO.sub.4 (Example 1). BaSO.sub.4 was used as reference.

[0154] FIG. 16: Reflection spectrum of Ca.sub.0.96Pr.sub.0.01Gd.sub.0.01Na.sub.0.02Li.sub.2SiO.sub.4 (Example 2). BaSO.sub.4 was used as reference.

[0155] FIG. 17: Reflection spectrum of Sr.sub.0.98Pr.sub.0.01Na.sub.0.01Li.sub.2SiO.sub.4 (Example 3). BaSO.sub.4 was used as reference.

[0156] FIG. 18: Reflection spectrum of Sr.sub.0.96Pr.sub.0.01Gd.sub.0.01Na.sub.0.02Li.sub.2SiO.sub.4 (Example 4). BaSO.sub.4 was used as reference.

[0157] FIG. 19: Excitation spectrum of Ca.sub.0.98Pr.sub.0.01 Na.sub.0.01Li.sub.2SiO.sub.4 monitoring emission at 300 nm (Example 1).

[0158] FIG. 20: Excitation spectrum of Ca.sub.0.96Pr.sub.0.01Gd.sub.0.01Na.sub.0.02Li.sub.2SiO.sub.4 monitoring emission at 312 nm (Example 2).

[0159] FIG. 21: Excitation spectrum of Sr.sub.0.98Pr.sub.0.01 Na.sub.0.01Li.sub.2SiO.sub.4 monitoring emission at 320 nm (Example 3).

[0160] FIG. 22: Excitation spectrum of Sr.sub.0.96Pr.sub.0.01Gd.sub.0.01Na.sub.0.02Li.sub.2SiO.sub.4 monitoring emission at 312 nm (Example 4).

[0161] FIGS. 23a/b: Increase of crystallinity of CaLi.sub.2SiO.sub.4:Pr.sup.3+ via high-energy milling (200 U/min, 4 h) and reduction of additional phases as impurity.

[0162] FIGS. 24 a/b/c: Particle size distribution of CaLi.sub.2SiO.sub.4:Pr.sup.3+ a) 100 U/min, 4 h b) 200 U/min, 4 h, c) increased emission with increased purity of phase and increased crystallinity.

[0163] FIGS. 25 a/b/c: a) increased emission with increased purity of phase and increased crystallinity, b) reduction of additional phases as impurities and increased crystallinity c) Particle size distribution of CaLi.sub.2SiO.sub.4:Pr.sup.3+ (200 U/min, 4 h)

[0164] FIG. 26: Simplified energy level scheme of Pr.sup.3+ (ground state configuration [Xe]4f.sup.2) and Gd.sup.3+ (ground state configuration [Xe]4f.sup.7) showing the relevant optical transitions and energy transfer processes involved in the up-conversion mechanism resulting in UV emission.

[0165] FIGS. 27a and 27b: a) above: XRPD of educts before milling, below XRPD CaLi.sub.2SiO.sub.4 calculated, b) XRPD milled educts, below: XRPD CaLi.sub.2SiO.sub.4 calculated.

[0166] FIGS. 27c and 27d: c) above: silicate-based lanthanide ion doped material heating (calcination) of milled for 12 h at 850° C. in air, reflex 2Θ=37.39° with 13357 counts, below: XRPD CaLi.sub.2SiO.sub.4 calculated, d) above: second heating 6 h, 850° C. forming gas (H.sub.2 (5%)/N.sub.2 (95%)), reflex 2Θ=37.39° with 15423 counts, below: XRPD CaLi.sub.2SiO.sub.4 calculated.

[0167] FIG. 27e: e) above: further grinding decrease the crystallinity: reflex 2Θ=37.39° reduced to 13576 counts, below: below: XRPD CaLi.sub.2SiO.sub.4 calculated.

[0168] FIGS. 28a and 28b: a) above: silicate-based lanthanide ion doped material (CaLi.sub.2SiO.sub.4:Pr.sup.3+, Na.sup.+) heating (calcination) for 12 h at 850° C. in air and afterwards in a reducing atmosphere at elevated temperature (H.sub.2/inertgas, 6 h 850° C., not milled): reflex 2Θ=37.39° 10964 counts; below: XRPD CaLi.sub.2SiO.sub.4 calculated, b) above: milled silicate-based lanthanide ion doped material after tempering in reducing atmosphere: reflex 2Θ=37.39° 18665 counts, (milling: 4 h 200 rpm, CaLi.sub.2SiO.sub.4:Pr.sup.3+, Na.sup.+), below: XRPD CaLi.sub.2SiO.sub.4 calculated