Process for preparing up-conversion phosphors

Abstract

To provide an optimized process for the preparation of up-conversion phosphors.SOLUTION: There is provided a process for preparing an up-conversion phosphor of the general formula (I): A1-x-y-zB*yB2SiO4: Ln1x, Ln2z, I. The process includes the steps of: 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).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for preparing an upconversion phosphor. [Background technology]

[0002] Every day, humans are exposed to millions of microorganisms, such as bacteria, fungi, and viruses. Many of these microorganisms are beneficial or even necessary. Nevertheless, besides these less harmful representatives, there are also bacteria, fungi, and viruses that can cause illness or even death.

[0003] Microorganisms can be transmitted through everyday interactions with other people and through contact with objects used by others. In places where hygiene is particularly important, surfaces are treated with an antibacterial finish. Areas of use are in particular the surfaces of medical equipment and consumer goods in hospitals and outpatient health and welfare facilities. In addition to these, there are surfaces in the public sphere, the food and beverage sector, and animal husbandry. The spread of pathogenic microorganisms is nowadays a major challenge in the care sector and in healthcare, as well as wherever humans are active in confined spaces. A particular current risk is the increasing occurrence of so-called multidrug-resistant bacteria, which are insensitive to standard antibiotics.

[0004] In addition to standard hygiene measures, antimicrobial technologies and materials are used to reduce the risk of pathogen spread through contact surfaces. The use of chemicals and physical methods can have a significant effect on the growth process of microorganisms. Physical methods include, for example, heat, cold, radiation, or ultrasound. Among chemical methods, halogens, metal ions, organic compounds and dyes, and toxic gases are known.

[0005] Although chemical and physical methods are in most cases highly effective in destroying microorganisms, their effectiveness is short-lived, and chemical methods promote the development of resistance and lead to the destruction of the surfaces they are intended to protect, making them unsuitable for some applications under some circumstances. However, the greatest drawback, especially in the case of organic chemicals, is their risk or toxicity to humans. Certain substances, such as formaldehyde, which have been used as disinfectants for many years, are now suspected of causing cancer or being extremely harmful to the environment.

[0006] Antimicrobial surfaces can make an important contribution to solving these challenges. Current standard methods for generating such antimicrobial properties primarily utilize active ingredients incorporated into materials, such as silver particles, copper particles, their metal oxides, or quaternary ammonium compounds. This often involves processing antimicrobial metals, antimicrobial metal oxides, or antimicrobial metal oxide mixtures to obtain nanoparticles that are then incorporated into paints, coatings, or polymeric materials. The widespread use of metal particles is questionable because it is nearly impossible to assess the long-term effects of these heavy metals on humans and the environment.

[0007] For example, WO 2019 / 197076 discloses particles finished with a layer containing both antimony tin oxide and manganese oxide. Those skilled in the art will recognize that the antibacterial surface is created due to the electrochemical properties of metals, which in the presence of moisture create microscale galvanic cells, resulting in a microscale electric field that produces a bactericidal action.

[0008] Similarly, it is known that UV irradiation can be used in medicine and hygiene, for example, to disinfect water, gas, or surfaces. For example, UV irradiation has long been used in drinking water treatment to reduce the number of facultative pathogenic microorganisms in water. This is preferably done using UV-C irradiation in the wavelength range of 200 nm to 280 nm. The use of different wavelengths of electromagnetic radiation should take into account the different absorption behaviors of amino acids / nucleic acids (e.g., DNA or RNA) and peptide bonds between individual acids present in various proteins, microorganisms, tissues, or cells. For example, DNA / RNA absorbs electromagnetic radiation well in the wavelength range of 200 nm to 300 nm, and especially well in the wavelength range of 250 nm to 280 nm, making this radiation particularly suitable for inactivating DNA / RNA. Therefore, such irradiation can inactivate pathogenic microorganisms (e.g., viruses, bacteria, yeast, and molds, among others). Depending on the duration and intensity of irradiation, the structure of DNA or RNA can be disrupted. Therefore, metabolically active cells can be inactivated and / or their proliferation ability can be lost. The advantage of UV irradiation is that microorganisms cannot develop resistance to UV light, but these physical methods require specialized equipment and generally must be repeated periodically by trained personnel, which makes these methods difficult to use widely.

[0009] Furthermore, as well as direct irradiation with electromagnetic radiation from the ultraviolet wavelength range, the use of the so-called upconversion effect is also known, which involves the use of phosphor particles that are able to convert electromagnetic radiation with wavelengths above ultraviolet, in particular visible light or infrared light, into electromagnetic radiation with shorter wavelengths, so that the individual phosphor particles emit radiation with the desired wavelength.

[0010] German Patent No. 102015102427 relates to an emitter of electromagnetic radiation in the wavelength range of UV light. Phosphor particles are embedded in the near-surface region of the material forming the emitter or in the coating of the emitter. It generally states that the phosphor particles are added directly to the coating formed on the material during processing, and that the specific material should have a suitable consistency or viscosity. German Patent No. 102015102427 does not mention suitable polymers and additives.

[0011] U.S. Patent Application Publication No. 2009 / 0130169A1 and WO 2009 / 064845A2 describe phosphors that can be incorporated into polyvinyl chloride, acryloylbutadiene, polyolefins, polycarbonates, styrene, or nylon, which kill pathogenic microorganisms through the phosphor's upconversion properties. These phosphors are prepared at temperatures between 1800 and 2900°C. U.S. Patent Application Publication No. 2009 / 0130169A1 and WO 2009 / 064845A2 disclose compositions containing the phosphors that are alleged to have antibacterial properties, but provide no evidence of upconversion properties or microbiological testing. The methods disclosed in these documents produce amorphous and glassy products instead of phosphors with upconversion properties.

[0012] Furthermore, U.S. Patent Application Publication No. 2009 / 0130169A1 and WO 2009 / 064845A2 are silent about the compatibility of the components in the coating composition and the properties of the coating surface, such as the paint surface, but the appearance of the coating surface is of utmost importance to consumers.

[0013] The requirements for coatings and paints are diverse. In principle, a coating or paint coating has two tasks or functions: protective and decorative. Hereinafter, when the term "coating" is used, both types of coatings are intended. They decorate, protect, and preserve materials such as wood, metal, or plastic. Therefore, on the one hand, a bright and glossy coating is required, while on the other hand, a continuous coating is required to ensure chemical and mechanical stability, consistent slippage, or a specific tactile feel.

[0014] In contrast to WO 2009 / 064845A2, patent application PCT / EP2020 / 077798 discloses phosphors exhibiting upconversion and their preparation. When irradiated with electromagnetic radiation having lower energy and longer wavelengths in the range of 2000 nm to 400 nm, in particular in the range of 800 nm to 400 nm, such phosphors can emit electromagnetic radiation having higher energy and shorter wavelengths in the range of 400 nm to 100 nm, preferably in the range of 300 nm to 200 nm, making them suitable for use as antibacterial phosphors in coating layers.

[0015] For example, EP 3929254 describes compositions comprising at least one film-forming polymer, at least one upconversion phosphor according to the teachings of PCT / EP2020 / 077798, optionally at least one additive, and optionally at least one curing agent. Coating layers containing these phosphors have been shown to have antibacterial activity without significantly impairing other properties, particularly storage stability.

[0016] However, it has also been found that phosphors prepared by the method according to PCT / EP2020 / 077798 exhibit a non-uniform particle size distribution, which creates particular challenges when incorporating these phosphors into a coating matrix. While the teachings of EP 3929254 result in an antimicrobial coating layer, it would further be desirable to be able to increase the intensity of the phosphor emission.

[0017] Pre-published European Patent Application No. 21167984.0 at least one film-forming polymer, optionally at least one additive, optionally at least one hardener, at least one upconversion phosphor, It is proposed to be used for the production of coatings with antibacterial properties, containing up to 3.5% by weight of flux relative to the total amount of reactants.

[0018] While the above publications and unpublished European Patent Application No. 21167984.0 all describe methods for preparing these upconversion phosphors, these methods have only been performed on a laboratory scale. This involved the use of an agate mortar and a muffle furnace. The dimensions of such equipment are naturally limited. Therefore, these methods cannot be optimally used for the industrial preparation of upconversion phosphors. The process is impractical, time-consuming, and costly. Furthermore, upconversion phosphors prepared in relatively large quantities by these methods have been found to be unreproducible. The materials either did not exhibit sufficient upconversion or had insufficient antibacterial activity. [Prior art documents] [Patent documents]

[0019] [Patent Document 1] International Publication No. 2019 / 197076 Brochure [Patent Document 2] German Patent No. 102015102427 [Patent Document 3] US Patent Application Publication No. 2009 / 0130169A1 [Patent Document 4] International Publication No. 2009 / 064845A2 Pamphlet [Patent Document 5] PCT / EP2020 / 077798 [Patent Document 6] European Patent No. 3929254 [Patent Document 7] Pre-published European Patent Application No. 21167984.0 Summary of the Invention [Problem to be solved by the invention]

[0020] Therefore, it was an object of the present invention to specify an optimized method for the preparation of upconversion phosphors. [Means for solving the problem]

[0021] To this end, compounds of general formula (I) A 1-x-y-z B* y B2SiO4:Ln 1 x, Ln 2 z, I (In the formula, x=0.0001-0.0500; z = 0.0000 or z = 0.0001 to 0.3000, where 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, and B is the same as B* or B is not the same as B*, preferably B and B* are not the same; Ln 1 is selected from the group consisting of praseodymium (Pr), erbium (Er), and neodymium (Nd); Ln 2 is selected from gadolinium (Gd) 1. A method for preparing an upconversion phosphor of claim 1, comprising the steps of: -Mixture: i) at least one lanthanoid salt and / or lanthanoid oxide selected from lanthanoid nitrates, lanthanoid carbonates, lanthanoid carboxylates, preferably lanthanoid acetates and lanthanoid sulfates, particularly preferably PrO 11 and / or Gd2O3, in which the lanthanide ions in the lanthanide oxide or lanthanide salt are selected from praseodymium, gadolinium, erbium, neodymium, and in the case of co-doping, at least two of these, and ii) a silicate, preferably a silicate salt, particularly preferably an alkali metal silicate salt, or silicon dioxide; iii) at least one alkaline earth metal salt and at least one alkali metal salt selected from lithium salts or lithium compounds, optionally selected from sodium and potassium salts, preferably alkali metal silicates or alkali metal carbonates, preferably salts of lithium salts, preferably lithium silicate, particularly preferably lithium carbonate, calcium carbonate and sodium carbonate, and optionally iv) at least one flux selected from the group consisting of ammonium halides, preferably ammonium chloride, alkali metal halides, preferably sodium chloride, sodium fluoride, sodium bromide, lithium fluoride or lithium chloride, alkaline earth metal halides, preferably calcium chloride or calcium fluoride, and lanthanide halides, preferably praseodymium fluoride or praseodymium chloride; and preparing the compound using - introducing the mixture into a reaction chamber of a thermal device; heating the mixture using a heat ramp at a rate of -10°C / h to 400°C / h, preferably 50°C / h to 350°C / h, particularly preferably 80°C / h to 300°C / h, until a heat treatment temperature of 600°C to less than 1000°C, preferably 650°C to 900°C is reached; - heat treating the heated mixture at a temperature between 600 ° C and less than 1000 ° C, preferably between 650 ° C and 900 ° C, with a holding time of at least 0.02 hours; cooling the heat-treated material to room temperature while maintaining a cooling ramp of between -10°C / hr and 400°C / hr, preferably between 50°C / hr and 350°C / hr, and particularly preferably between 80°C / hr and 300°C / hr; - obtaining a silicate-based lanthanide ion-doped phosphor according to formula (I); The present invention relates to a method comprising:

[0022] The term "heat treatment" is understood herein to mean calcination, pre-calcination, heat treatment or thermal reduction. The method according to the invention now surprisingly makes it possible to prepare reproducible amounts of upconversion phosphors.

[0023] An advantage of the method according to the invention is that the device material is protected due to the heating and cooling ramps, so that the devices used are not subjected to sudden temperature stresses that could lead to material fatigue.

[0024] Preferably, the holding time is 0.5 hours, preferably 3 hours, particularly preferably 6 hours or 12 hours, but not more than 48 hours. Therefore, those skilled in the art can vary the holding time within these times for economic reasons.

[0025] During the holding time, the heat treatment temperature is preferably kept constant.

[0026] The mixture can be preferably prepared by batch mixers such as drum hoop mixers, drum roller mixers, double cone mixers, container mixers, drum mixers, or continuous mixers such as paddle mixers, extruders, and flow mixers. Other mixers are also contemplated.

[0027] The mixture is preferably prepared without a solvent.

[0028] Preferably, the mixture is ground and / or compressed before being introduced into the reaction chamber.

[0029] The homogeneity of the mixture before introduction into the reaction chamber can play a major role in achieving the required product quality. To achieve this homogeneity, milling is preferably used to achieve a more uniform particle size distribution of components i, ii, iii, and optionally iv. Milling can be carried out by wet milling or dry milling. Dry milling can be carried out, for example, in a ball mill, stirred ball mill, pinned disk mill, impact mill, sifter mill, spiral jet mill, fluidized bed jet mill, or steam jet mill. Wet milling can be carried out, for example, in a rotor-stator disperser / disperser, stirred ball mill, or colloid mill.

[0030] Subsequent compaction / granulation has the advantage of reducing the required working volume of the oven, preventing or minimizing dust formation, and / or preventing demixing of the ingredients. Compaction can be carried out wet or dry. Compacted powders, resulting in and containing granules, can be prepared by compaction. A roller press / compactor or similar technology can be used for compaction.

[0031] Preferably, at least 0.01% to 10.0% by weight, preferably at least 0.5% to 6.0% by weight, particularly preferably 1.5% to 4.0% by weight of flux is used, based on the total amount of reactants.

[0032] The thermal treatment is preferably carried out in a batch or continuous manner. Depending on the geometry of the thermal equipment, one such method may be advantageous and can be evaluated and used accordingly by those skilled in the art.

[0033] The thermal device is preferably a batch furnace, preferably a muffle furnace, air circulation furnace, chamber furnace, trolley hearth furnace or fluidized bed furnace or reactor, or a continuous furnace, preferably a push-through furnace, flow-through furnace, rotary tube furnace, drum furnace, tunnel furnace, vertical furnace or paternoster furnace.

[0034] These furnaces may preferably be constructed to be airtight and / or gas-permeable and may be powered by electricity or natural gas.

[0035] The furnace structure should preferably be such that the method according to the invention, which essentially consists of heating, heat treatment and cooling, can be carried out in accordance with the respective ramp and hold times.

[0036] When using a rotary tube furnace or drum furnace, it is preferable to first heat the working tube or drum without the mixture. Once the working tube reaches the required temperature, the mixture is introduced. Due to its structure, its holding time can be shortened, resulting in a correspondingly high throughput. Since the product is immediately fed into the vessel, the cooling step of the present invention with a cooling lamp can be omitted.

[0037] Preferably, the heat treatment is carried out in a rotary tube furnace in combination with further batch or continuous furnaces, such as tunnel furnaces, flow-through furnaces, push-plate furnaces, etc.

[0038] The heat treatment is preferably carried out completely or partly in an air atmosphere.

[0039] If the process according to the invention is carried out in a reducing atmosphere, the thermal device should preferably be gas-tight.

[0040] When carried out under an air atmosphere, the gas permeability of the thermal device may be advantageous.

[0041] It is envisaged that the process according to the invention is preferably carried out under an air atmosphere and a reducing atmosphere, and the thermal device should have such a combined unit for this purpose.

[0042] Preferably, the thermal device in the reaction chamber comprises one or more containers made of ceramic and / or provided with a ceramic filler and / or a ceramic coating. Containers made of other materials that do not react with the reactants and / or products may also be used. These containers may be stationary or mobile within the reaction chamber (e.g., on a paternoster lift, on a carriage, on a continuous belt, etc.).

[0043] If more than 1.0% by weight of lanthanide ions are used relative to the total amount of reactants, it is preferred to carry out a further heat treatment before cooling the heat-treated material in a reducing atmosphere at a temperature between 600°C and less than 1000°C, preferably between 650°C and 900°C, with a holding time of at least 0.02 hours, preferably at least 0.5 hours, particularly preferably at least 3 hours.

[0044] The reducing atmosphere is preferably a CO-containing atmosphere or forming gas, preferably an argon-hydrogen mixture or a nitrogen-hydrogen mixture (97 / 3 and 95 / 5).

[0045] In the process according to the invention, the lanthanide is preferably praseodymium, the alkali metal is preferably sodium or lithium, and the alkaline earth metal is preferably calcium.

[0046] Preferred silicon dioxides that can be used are products having the trade names Aerosil® 300, 200, OX50, 200V and 300V from Evonik.

[0047] Preferably, the phosphors prepared by the method according to the present invention are doped with praseodymium.

[0048] Preferably, the cooled silicate-based lanthanide ion doped phosphor is milled.

[0049] The phosphors prepared by the method according to the present invention can be coated by post-treatment. The coated and uncoated up-conversion phosphors can be used in coating materials with antibacterial activity.

[0050] Presented below are examples that serve only to elucidate the invention to one of ordinary skill in the art and do not constitute any limitation on all of the claimed subject matter. [Brief explanation of the drawings]

[0051] [Figure 1] FIG. 1 shows the emission spectrum of a phosphor prepared by the method according to the present invention. [Example]

[0052] method Particle size distribution according to ISO 13320:2020 and USP 429 using a Horiba LA-950 laser particle size analyzer Qualitative elemental analysis by EDX using a Hitachi Tabeltop 4000Plus, 15kV BSE detector, and 1000x magnification; Powder XRD: The X-ray powder diffraction pattern of the sample was Cu-K α The data were recorded using a Bruker D2 Phaser powder diffractometer operating in Bragg-Brentano geometry using a radiation and line scan CCD detector, with an integration time of 20 seconds and a step size of 0.017° 2θ. Emission spectra were recorded using an Edinburgh Instruments FLS920 spectrometer equipped with a Coherent 488 nm continuous wave OBIS laser and a Hamamatsu Peltier-cooled (-20 °C) single-photon counting photomultiplier tube (R2658P). Edge filters were used to suppress second- and higher-order reflections caused by the monochromator. BET surface area measurements according to ISO 9277:2010, DIN 66131 using a Quantachrome Nova 2000e instrument. The degree of crystallinity (DOC) gives information about the ratio of the crystalline area to the amorphous area of ​​all components in the powder diffraction pattern. The degree of crystallinity is calculated from the total area under the crystalline and amorphous fractions.

[0053]

number

[0054] Bulk and compacted density determination according to DIN EN ISO 787-11:1995-10. The production of phosphor (CaF2) containing 1.5 wt. % as flux on a 6 kg scale by the method according to the invention 0.98 Pr 0.01 Na 0.01 ) Preparation example of Li2SiO4 CaCO32.47kg, Li2CO31.86kg, SiO21.51kg, Na2CO313.36g, Pr6O 1142.95g of CaF292.62g was mixed in a drum hoop mixer and ground using a pinned disc mill. The ground mixture was then compacted using a roller compactor. The ground and compacted mixture was distributed into three 3.2 L ceramic boxes. Each box was filled with 2 kg of the mixture. The boxes were then transferred to a chamber furnace. The filled box (batch) was heated to a temperature of 850°C using a heating ramp of 90°C / h. Once the heat treatment temperature of 850°C was reached, the batch was fired in air for 6 hours. The phosphor was then cooled to room temperature while maintaining a cooling ramp of 90°C / h. The cooled raw phosphor material was removed from the box and could be pre-ground using a jaw crusher. The pre-ground phosphor was then crushed using an air jet mill. D 10 :2.6μm D 50 :3.6μm D 90 :6μm The powder was ground to a particle size distribution of A 6 kg batch of reactants produced a yield of 4.8 kg of phosphor. The phosphors prepared by the method according to the present invention exhibited up-conversion properties in the emission spectrum in the UV-C range and antibacterial activity.

[0055] Theoretical Comparative Example 1 (CE1) A phosphor (CaF2) with 1.5 wt. % as flux according to unpublished European patent application EP 21167984.0 0.98 Pr 0.01 Na 0.01 ) Preparation of Li2SiO4 For a 6 kg batch of reactants, theoretically, 600 crucibles would need to be prepared and 200 muffle furnaces would need to be present in order for the process to be viable. This calculation was based on the capacity of the muffle furnaces. Theoretically, three 60 ml ceramic crucibles could fit into the muffle furnace, each capable of containing 10 g of reaction mixture. Taking this calculation into account, it is clear that the processes known from the prior art were not economically viable.

[0056] Comparative Example 2 (CE2): Phosphor with 1.5 wt. % CaF as flux (CaF) on a 6 kg scale without heat lamps and without cooling lamps 0.98 Pr 0.01 Na 0.01 ) Preparation of Li2SiO4 The reactants were mixed and distributed into 3.2 L ceramic boxes as in the previous examples. However, the heat lamp was omitted. It was found that all the ceramic boxes were broken. After the heat treatment, the phosphor was cooled to room temperature without maintaining the cooling lamp. The damaged ceramic boxes were irreparably damaged. A yield of 0 kg of phosphor was obtained. The phosphor contaminated with ceramic material was discarded.

Claims

1. General formula (I) A １－ｘ－ｙ－ｚ B* ｙ B ２ SiO ４ :Ln １ ｘ， Ln ２ ｚ， I (In the ceremony x=0.0001-0.0500; z=0.0000 or z=0.0001 to 0.3000, where 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, and B is the same as B* or B is not the same as B*; Ln １ is selected from the group consisting of praseodymium (Pr), erbium (Er), and neodymium (Nd); Ln ２ is selected from gadolinium (Gd) 1. A method for preparing an upconversion phosphor of claim 1, comprising the steps of: -below: i) at least one lanthanoid salt and / or lanthanoid oxide selected from lanthanoid nitrates, lanthanoid carbonates, lanthanoid carboxylates, and lanthanoid sulfates, in which the lanthanoid ions in the lanthanoid oxide or lanthanoid salt are selected from praseodymium, gadolinium, erbium, neodymium, or in the case of co-doping, at least two of these; ii) silicate or silicon dioxide; iii) at least one alkaline earth metal salt and at least one alkali metal salt or alkali metal carbonate, and optionally iv) at least one flux selected from the group consisting of ammonium halides, alkali metal halides, alkaline earth metal halides, and lanthanide halides; preparing a mixture using - introducing said mixture into a reaction chamber of a thermal device; heating the mixture using a heat ramp of -10°C / hr to 400°C / hr until a heat treatment temperature of 600°C to less than 1000°C is reached; - heat treating the heated mixture at a temperature of 600°C to less than 1000°C, with a holding time of at least 0.02 hours; cooling the heat treated material to room temperature while maintaining a cooling ramp of -10°C / hr to 400°C / hr; - obtaining a silicate-based lanthanide ion-doped phosphor according to formula (I), A method comprising:

2. 10. The method of claim 1, wherein the mixture is prepared without a solvent.

3. 2. The method of claim 1, wherein the mixture is ground and / or compressed before being introduced into the reaction chamber.

4. 2. The method of claim 1, wherein at least 0.01% to 10.0% by weight of flux is used relative to the total amount of reactants.

5. 2. The method of claim 1, wherein the heat treatment is carried out batchwise or continuously.

6. 2. The method of claim 1, wherein the thermal device is a batch furnace or a continuous furnace.

7. 2. The method according to claim 1, characterized in that when a rotary tube furnace or drum furnace is used, it is necessary to heat the working tube or drum before introducing the mixture.

8. 2. The method of claim 1, wherein the heat treatment is carried out in an air atmosphere.

9. 2. The method of claim 1, characterized in that when more than 1.0 wt. % lanthanide ions are used relative to the total amount of reactants, a further heat treatment is carried out under a reducing atmosphere at a temperature of 600° C. to less than 1000° C. with said holding time of at least 0.02 hours before said cooling of said heat-treated material.

10. 10. The method of claim 9, wherein the reducing atmosphere is a CO-containing atmosphere or forming gas.

11. 2. The method of claim 1, wherein the lanthanide is praseodymium.

12. 2. The method of claim 1, wherein the alkali metal is sodium or lithium.

13. 2. The method of claim 1, wherein the alkaline earth metal is calcium.

14. 2. The method of claim 1, wherein said phosphor is doped with praseodymium.

15. 10. The method of claim 1, wherein the cooled silicate-based lanthanide ion-doped phosphor is milled.

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