Process for production of magnesium fluoride sol solutions from alkoxides comprising addition of magnesium salts

Abstract

The invention relates to a method for obtaining a magnesium fluoride (MgF.sub.2) sol solution, comprising the steps of providing a magnesium alkoxide precursor in a non-aqueous solvent and adding 1.85 to 2.05 molar equivalents of non-aqueous hydrofluoric acid, characterized in that the reaction proceeds in the presence of a second magnesium fluoride precursor selected from the group of salts of strong, volatile acids, such as a chloride, bromide, iodide, nitrate or triflate of magnesium, or of a catalytic amount of a strong, volatile acid; and/or an additive non-magnesium fluoride precursor selected from the group of salts of strong, volatile acids, such as a chloride, bromide, iodide, nitrate or triflate of lithium, antimony, tin calcium, strontium, barium, aluminum, silicon, zirconium, titanium or zinc. The invention further relates to sol solutions, method of applying the sol solutions of the invention to surfaces as a coating, and to antireflective coatings obtained thereby.

Claims

1. A method for obtaining a magnesium fluoride (MgF.sub.2) sol solution, comprising the steps of (a) providing a magnesium alkoxide in a non-aqueous solvent in a first volume and (b) adding, in a second volume, 1.85 to 2.05 molar equivalents of anhydrous hydrogen fluoride (HF) to said magnesium alkoxide, wherein (c) the reaction proceeds in the presence of (i) a second magnesium fluoride precursor selected from the group consisting of chloride, bromide, iodide, nitrate and triflate of magnesium, and/or (ii) at least one additive non-magnesium fluoride precursor selected from the group consisting of chloride, bromide, iodide, nitrate or triflate of lithium, antimony, tin, calcium, strontium, barium, aluminium, silicon, zirconium, titanium and zinc, wherein said additive second magnesium fluoride precursor or additive non-magnesium fluoride precursor is present in a quantity ranging from 1% to 20% as measured in molar equivalents of said magnesium alkoxide.

2. The method according to claim 1, wherein said second magnesium fluoride precursor is slected from the group consisting of a chloride, a bromide, an iodide, a nitrate, and a triflate of Mg.sup.2+ and said additive non-magnesium fluoride precursor is selected from the group consisting of a chloride, a bromide, an iodide and a nitrate of Li.sup.+, Ca.sup.2+, Sr.sup.2+, Ba.sup.2+, Zn.sup.2+, Al.sup.3+, Si.sup.4+, Zr.sup.4+, Sn.sup.4+, Sb.sup.3+, Sb.sup.5+, or Ti.sup.4+.

3. The method according to claim 1, wherein an additional amount of hydrogen fluoride (n.sub.adHF) is present in the fluorination of step b computed according to the formula
n.sub.adHF=(n.sub.M*.sub.additive)*Ox*A, wherein n.sub.M is the molar amount of said magnesium alkoxide, .sub.additive is the molar percentage of said second magnesium fluoride precursor or said non-magnesium fluoride precursor, wherein .sub.additive is in the range of 1% to 20%, and Ox is the oxidation state of the metal of said second magnesium fluoride precursor or said non-magnesium fluoride precursor, and A is selected from 0A1.

4. The method according to claim 1, wherein the reaction proceeds in the presence of a catalytic amount of a strong, volatile acid.

5. The method according to claim 1, wherein said non-aqueous solvent is ethanol and/or the water content of the sol solution is equal to or lower than 2.0 molar equivalents in relation to the magnesium content of the solution.

6. A method for coating a surface, comprising the steps of (a) providing a magnesium fluoride sol solution produced by the method according to claim 1; (b) contacting said surface with said magnesium fluoride sol solution; (c) drying said surface; (d) exposing said surface in a first thermal step to a first temperature ranging from 15 C. to 480 C., from 10 C. to 100 C., or from 250 C. to 480 C.

7. The method for coating a surface according to claim 6, wherein after said first thermal step, a second thermal step is applied wherein said surface is exposed to a second temperature ranging from 250 C. to 480 C.

8. A method for obtaining a magnesium fluoride (MgF.sub.2) sol solution, comprising the steps of (a) providing a magnesium alkoxide in a non-aqueous solvent in a first volume and (b) adding, in a second volume, 1.85 to 2.05 molar equivalents of anhydrous hydrogen fluoride (HF) to said magnesium alkoxide, wherein (c) the reaction proceeds in the presence of (i) at least one additive non-magnesium fluoride precursor selected from the group consisting of chloride, bromide, iodide, nitrate or triflate of calcium, strontium, barium, aluminum, silicon, zirconium, titanium and zinc, wherein said additive non-magnesium fluoride precursor is present in a quantity ranging from 1% to 20% as measured in molar equivalents of said magnesium alkoxide.

Description

SHORT DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows the change in the optical transmittance of a coated material as a function of the refractive index of the thin film;

(2) FIG. 2 shows a typical MgF.sub.2-particle size distribution determined by DLS;

(3) FIG. 3 shows a typical XRD-diffractogramm of a MgF.sub.2-Xerogel obtained from a magnesium ethylate based MgF.sub.2-Sol;

(4) FIG. 4 shows a typical .sup.19F-NMR-spectrum during the synthesis of a MgF.sub.2 sol indicating the stage of completeness of MgF.sub.2-formation (the chemical shift at 198 ppm represents pure MgF.sub.2, and only the d and e graphs correspond to stoichiometric near ratios (d: F/M=1.95 and e: F/Mg=2.0));

(5) FIG. 5 .sup.19F NMR spectra of MgF.sub.2-sols prepared from Mg(OC.sub.2H.sub.5) and MgCl.sub.2 (prepared according to the general synthesis described in example 8);

(6) FIG. 6 .sup.19F NMR spectra of MgF.sub.2-sols prepared from Mg(OC.sub.2H.sub.5) plus MgCl.sub.2.6H.sub.2O (prepared according to the general synthesis described in example 9).

EXAMPLES

(7) Synthesis of Clear MgF.sub.2-Sols

(8) 1) 16.29 g commercial magnesium ethylate (MgOEt.sub.2) were suspended in 450 ml isopropanol. Then, 0.715 g MgCl.sub.2 were dissolved therein. To this suspension, 50 ml methanol containing 6.0 g anhydrous HF (aHF) were added under rigorous stirring. After 1 day stirring at room temperature, a clear MgF.sub.2-sol with a concentration of 0.3 mol/l was obtained. The kinematic viscosity of the sol was 1.1 mm.sup.2 s.sup.1 and did not change over a period of 10 weeks.
2) 16.25 g commercial magnesium ethylate (MgOEt.sub.2) were suspended in 450 ml isopropanol. Then, 0.715 g waterfree MgCl.sub.2 were dissolved therein. To this suspension, 50 ml ethanol containing 6.3 g anhydrous HF (aHF) were added under rigorous stirring. After 1 day stirring at room temperature, a clear MgF.sub.2-sol with a concentration of 0.3 mol/l was obtained. The kinematic viscosity of the sol was 1.1 mm.sup.2 s.sup.1 and did not change over a period of 10 weeks.
3) 16.29 g commercial magnesium ethylate (MgOEt.sub.2) and 0.83 g calcium chloride were first suspended in 400 ml ethanol. To this solution 50 ml ethanol containing 6.0 g aHF were added (molar ratio n.sub.HF/(n.sub.Ca2++n.sub.Mg2+)=2; n.sub.Mg2+/n.sub.Ca2+=9/1). A clear sol formed inside only about 30 minutes having a concentration of 0.3 related to the whole 2+ metal cations and of 5 mol % Ca related to Mg. The kinematic viscosity of the sol was ca. 1.4 mm.sup.2 s.sup.1 and remained unchanged over 6 weeks.
3) 15.4 g commercial magnesium ethylate and 1.67 g waterfree calcium chloride were first suspended in 450 ml ethanol. To this solution 50 ml ethanol containing 6 g aHF were added (molar ratio n.sub.HF/(n.sub.Ca2++n.sub.Mg2+)=2; n.sub.Mg2+/n.sub.Ca2+=9/1). A clear sol formed inside only about 4 hours having a concentration of 0.3 related to the whole M.sup.2+ cations. The kinematic viscosity of the sol was ca. 1.4 mm.sup.2 s.sup.1 and remained unchanged over 6 weeks. Following the same synthesis procedure, MgF.sub.2-sols based on different amount of added CaCl.sub.2 were obtained by changing the Mg(OC.sub.2H.sub.5).sub.2 to CaCl.sub.2 ratio but keeping the overall M.sup.2+-concentration (M=Mg.sup.2++Ca.sup.2+) and the amount of HF (molar HF/M ratio=2.0) and all the other reaction conditions constant. These results are summarized in the table 1.

(9) TABLE-US-00001 TABLE 1 In all batches magnesium ethylate and CaCl.sub.2 together gave 0.15 mol M.sup.2+ in 450 ml ethanol. In all batches 6 g HF in 50 ml ethanol were used (molar HF/Mg ratio = 2.0). Mg(OC.sub.2H.sub.5).sub.2 to clear viscosity mm.sup.2s.sup.1 No CaCl.sub.2molar ratio after hours after 6 weeks remarks a 95/5 16 1.3 stable viscosity b 90/10 4 1.3 stable viscosity c 80/20 3 1.4 stable viscosity
4) 17.5 g commercial magnesium ethylate and 1.5 g aluminium chloride were first suspended in 400 ml ethanol. To this solution 50 ml ethanol containing 6 g aHF were added. A clear sol formed within about 60 minutes exhibiting a concentration of 0.3 mol/l and having 5 mol % Al.sup.3+ related to MgF.sub.2. The kinematic viscosity of the sol was ca. 1.2 mm.sup.2 s.sup.1 and remained unchanged over 6 weeks.
4) 16.25 g commercial magnesium ethylate and 1 g waterfree aluminium chloride were first suspended in 400 ml ethanol. To this solution 50 ml ethanol containing 6 g aHF were added. A clear sol formed within about 60 minutes exhibiting a concentration of 0.3 mol/l and having 5 mol % Al.sup.3+ related to MgF.sub.2. The kinematic viscosity of the sol was ca. 1.2 mm.sup.2 s.sup.1 and remained unchanged over 6 weeks.
5) 15.5 g freshly prepared magnesium methylate plus 1.4 g dried MgCl.sub.2 were suspended in 450 ml ethanol. To this solution, 50 ml ethanol containing 8.0 g anhydrous HF (aHF) were added under rigorous stirring. After 24 hours stirring at room temperature, a clear ethanolic MgF.sub.2-sol with a concentration of 0.4 mol/l was obtained. The kinematic viscosity of the sol was 1.2 mm.sup.2 s.sup.1 and did not change over a period of 10 weeks.
6) 15.5 g freshly prepared magnesium methylate plus 1.7 g dried CaCl.sub.2 were suspended in 450 ml ethanol. To this solution, 50 ml ethanol containing 8.0 g anhydrous HF (aHF) were added under rigorous stirring. After 20 hours stirring at room temperature, a clear ethanolic MgF.sub.2-sol with a concentration of 0.36 mol/l with 10% CaF.sub.2 (overall MF.sub.2 concentration 0.4) was obtained. The kinematic viscosity of the sol was 1.3 mm.sup.2 s.sup.1 and did not change over a period of 10 weeks.
7) 17.2 g freshly prepared magnesium methylate plus 0.6 g dried LICl were suspended in 450 ml ethanol. To this solution, 50 ml ethanol containing 8.0 g anhydrous HF (aHF) were added under rigorous stirring. After 28 hours stirring at room temperature, a clear ethanolic MgF.sub.2-sol with a concentration of 0.4 mol/l containing 10 mol % LiCl was obtained. The kinematic viscosity of the sol was 1.3 mm.sup.2 s.sup.1 and did not change over a period of 10 weeks.
8) 16.25 g commercial magnesium ethylate were suspended in 450 ml ethanol. Then, 0.715 g waterfree MgCl.sub.2 were dissolved. To this suspension, 50 ml ethanol containing 6 g anhydrous HF (aHF) were added under rigorous stirring. After 1 day stirring at room temperature, a clear ethanolic MgF.sub.2-sol with a concentration of 0.3 mol/l was obtained. The kinematic viscosity of the sol was 1.1 mm.sup.2 s.sup.1 and did not change over a period of 10 weeks. Following the same synthesis procedure, MgF.sub.2-sols based on different amount of added waterfree MgCl.sub.2 were obtained by changing the Mg(OC.sub.2H.sub.5).sub.2 to MgCl.sub.2 ratio but keeping the overall Mg.sup.2+-concentration and the amount of HF (molar HF/Mg ratio=2.0) and all the other reaction conditions constant. These results are summarized in the table 2.

(10) TABLE-US-00002 TABLE 2 In all batches magnesium ethylate and MgCl.sub.2 together gave 0.15 mol Mg.sup.2+ in 450 ml ethanol. In all batches 6 g HF in 50 ml ethanol were used (molar HF/Mg ratio = 2.0). Mg(OC.sub.2H.sub.5).sub.2 to clear viscosity mm.sup.2s.sup.1 No MgCl.sub.2 molar ratio after hours after 6 weeks remarks a 95/5 24 1.4 stable viscosity b 90/10 18 1.4 stable viscosity c 80/20 12 1.5 stable viscosity
9) 16.25 g commercial magnesium ethylate were suspended in 450 ml ethanol. Then, 1.5 g magnesium chloride hexahydrate, MgCl.sub.2.6H.sub.2O, were dissolved. To this suspension, 50 ml ethanol containing 6 g anhydrous HF (aHF) were added under rigorous stirring. After 15 hours stirring at room temperature, a clear ethanolic MgF.sub.2-sol with a concentration of 0.3 mol/l was obtained. The kinematic viscosity of the sol was 1.2 mm.sup.2 s.sup.1 and did not change over a period of 10 weeks. Following the same synthesis procedure, MgF.sub.2-sols based on different amount of added MgCl.sub.2.6H.sub.2O were obtained by changing the Mg(OC.sub.2H.sub.5).sub.2 to MgCl.sub.2.6H.sub.2O ratio but keeping the overall Mg.sup.2+-concentration and the amount of HF (molar HF/Mg ratio=2.0) and all the other reaction conditions constant. These results are summarized in the table 3.

(11) TABLE-US-00003 TABLE 3 In all batches magnesium ethylate and MgCl.sub.26H.sub.2O together gave 0.15 mol Mg.sup.2+ in 450 ml ethanol. In all batches 6 g HF in 50 ml ethanol were used (molar HF/Mg ratio = 2.0). Mg(OC.sub.2H.sub.5).sub.2 to MgCl.sub.26H.sub.2O clear viscosity mm.sup.2s.sup.1 No molar ratio after hours after 6 weeks remarks a 95/5 24 1.4 stable viscosity b 90/10 15 1.3 stable viscosity c 80/20 10 1.4 stable viscosity
10) 16.25 g commercial magnesium ethylate were suspended in 450 ml ethanol. Then, 1.65 g calcium chloride hexahydrate, CaCl.sub.2.6H.sub.2O, were dissolved. To this suspension, 50 ml ethanol containing 6 g anhydrous HF (aHF) were added under rigorous stirring. After 2 hours stirring at room temperature, a clear ethanolic MgF.sub.2-sol with a concentration of 0.3 mol/l was obtained. The kinematic viscosity of the sol was 1.3 mm.sup.2 s.sup.1 and did not change over a period of 10 weeks. Following the same synthesis procedure, MgF.sub.2-sols based on different amount of added CaCl.sub.2.6H.sub.2O were obtained by changing the Mg(OC.sub.2H.sub.5).sub.2 to CaCl.sub.2.6H.sub.2O ratio but keeping the overall Mg.sup.2+-concentration and the amount of HF (molar HF/Mg ratio=2.0) and all the other reaction conditions constant. These results are summarized in the table 4.

(12) TABLE-US-00004 TABLE 4 In all batches magnesium ethylate and CaCl.sub.26H.sub.2O together gave 0.15 mol M.sup.2+ in 450 ml ethanol. In all batches 6 g HF in 50 ml ethanol were used (molar HF/Mg ratio = 2.0). Mg(OC.sub.2H.sub.5).sub.2 to CaCl.sub.26H.sub.2O clear viscosity mm.sup.2s.sup.1 molar ratio after hours after 6 weeks remarks 95/5 4 1.2 stable viscosity 90/10 2 1.3 stable viscosity 80/20 1 1.3 stable viscosity
11) 17.1 g commercial magnesium ethylate were first suspended in 400 ml ethanol. To this solution 50 ml ethanol containing 6 g aHF were added. Then immediately 1.56 g tetraethoxysilan (TEOS) were added. A clear sol formed within about 36 hours exhibiting a concentration of 0.3 mol/l and having 5 mol % Si.sup.4+ related to MgF.sub.2. The kinematic viscosity of the sol was ca. 1.5 mm.sup.2 s.sup.1 and remained unchanged over 6 weeks.
12) 17.1 g commercial magnesium ethylate were first suspended in 400 ml ethanol. To this solution 50 ml ethanol containing 6 g aHF were added. Then immediately 2.45 g zirconium-n-propylat (Zr(O.sup.nR).sub.4) were added. A clear sol formed within about 48 hours exhibiting a concentration of 0.3 mol/l and having 5 mol % Zr.sup.4+ related to MgF.sub.2. The kinematic viscosity of the sol was ca. 1.5 mm.sup.2 s.sup.1 and remained unchanged over 6 weeks.
13) 17.1 g commercial magnesium ethylate were first suspended in 400 ml ethanol. To this solution 50 ml ethanol containing 6 g aHF were added. Then immediately 2.13 g titaniumisopropoxide Ti[OCH(CH.sub.3).sub.2].sub.4 were added. A clear sol formed within about 40 hours exhibiting a concentration of 0.3 mol/l and having 5 mol % Ti.sup.4+ related to MgF.sub.2. The kinematic viscosity of the sol was ca. 1.4 mm.sup.2 s.sup.1 and remained unchanged over 6 weeks.
14) 16.6 g commercial magnesium ethylate and 0.5 g waterfree calcium chloride and 2.31 g titaniumisopropoxide Ti[OCH(CH.sub.3).sub.2].sub.4 were first suspended in 450 ml ethanol. To this solution 50 ml ethanol containing 6 g aHF were added (molar ratio n.sub.HF/(n.sub.Ca2++n.sub.Mg2+)=2; n.sub.Mg2+/n.sub.Ca2+=97/3). A clear sol formed inside of 18 hours having a concentration of 0.3 related to the whole M.sup.2+ cations. The content of Ti[OCH(CH.sub.3).sub.2].sub.4 related to the overall MF.sub.2-content was 5 mol %. The kinematic viscosity of the sol was ca. 1.3 mm.sup.2 s.sup.1 and remained stable over 6 weeks.
15) 16.6 g commercial magnesium ethylate and 0.5 g waterfree calcium chloride and 2.45 g zirconium-n-propylat (Zr(O.sup.nR).sub.4) were first suspended in 450 ml ethanol. To this solution 50 ml ethanol containing 6 g aHF were added (molar ratio n.sub.HF/(n.sub.Ca2++n.sub.Mg2+)=2; n.sub.Mg2+/n.sub.Ca2+=97/3). A clear sol formed inside of 26 hours having a concentration of 0.3 related to the whole M.sup.2+ cations. The content of Zr(O.sup.nR).sub.4 related to the overall MF.sub.2-content was 5 mol %. The kinematic viscosity of the sol was ca. 1.5 mm.sup.2 s.sup.1 and remained stable over 6 weeks.
16) 16.6 g commercial magnesium ethylate and 0.5 g waterfree calcium chloride and 1.56 g tetraethoxysilan (TEOS) were first suspended in 450 ml ethanol. To this solution 50 ml ethanol containing 6 g aHF were added (molar ratio n.sub.HF/(n.sub.Ca2++n.sub.Mg2+)=2; n.sub.Mg2+/n.sub.Ca2+=97/3). A clear sol formed inside of 12 hours having a concentration of 0.3 related to the whole M.sup.2+ cations. The content of TEOS related to the overall MF.sub.2-content was 5 mol %. The kinematic viscosity of the sol was ca. 1.5 mm.sup.2 s.sup.1 and remained stable over 6 weeks.
17) 16.6 g commercial magnesium ethylate and 0.5 g waterfree calcium chloride and 1.53 g aluminium isopropoxide Al[OCH(CH.sub.3).sub.2].sub.3 were first suspended in 450 ml ethanol. To this solution 50 ml ethanol containing 6 g aHF were added (molar ratio n.sub.HF/(n.sub.Ca2++n.sub.Mg2+)=2; n.sub.Mg2+/n.sub.Ca2+=97/3). A clear sol formed inside of 26 hours having a concentration of 0.3 related to the whole M.sup.2+ cations. The content of Al[OCH(CH.sub.3).sub.2].sub.3 related to the overall MF.sub.2-content was 5 mol %. The kinematic viscosity of the sol was ca. 1.4 mm.sup.2 s.sup.1 and remained stable over 6 weeks.
18) 16.6 g commercial magnesium ethylate and 0.5 g waterfree calcium chloride and 1.53 g aluminium isopropoxide Al[OCH(CH.sub.3).sub.2].sub.3 were first suspended in 450 ml ethanol. To this solution 50 ml ethanol containing 6.23 g aHF were added (molar ratio n.sub.HF/(n.sub.Ca2++n.sub.Mg2+)=2; and n.sub.HF/n.sub.Al3+=3/1, n.sub.Mg2+/n.sub.Ca2+=97/3). A clear sol formed inside of 20 hours having a concentration of 0.3 related to the whole M.sup.2+ cations. The content of Al[OCH(CH.sub.3).sub.2].sub.3 related to the overall MF.sub.2-content was 5 mol %. The kinematic viscosity of the sol was ca. 1.3 mm.sup.2 s.sup.1 and remained stable over 6 weeks.
19) Four different reactions systems were prepared consisting of 16.29 g commercial magnesium ethylate that was suspended in 450 ml ethanol each. Then, to these 4 suspensions MgCl.sub.2.6H.sub.2O was given (dissolved): a) 6.26 g, b) 1.566 g, c) 2.191 g, and c) 3.13 g. To this suspension, 50 ml ethanol containing a) 5.83 g, b) 6.00 g, c) 6.12 g, and d) 6.29 g anhydrous HF (aHF) were added under rigorous stirring. After 1 day stirring at room temperature, a clear ethanolic MgF.sub.2-sol with a concentration of 0.3 mol/l was obtained. The kinematic viscosity of the sol was 1.1 mm.sup.2 s.sup.1 and did not change over a period of 10 weeks.
MgF.sub.2-Sols without Addition of an Additive
A) 17.2 g freshly prepared magnesium methylate were suspended in 450 ml ethanol. To this suspension, 50 ml ethanol containing 8.0 g anhydrous HF (aHF) were added under rigorous stirring. No clear sol was obtained instead a turbid non-transparent suspension of large MgF.sub.2 particles was formed which did not clear up even after several weeks stirring.
B) 22.8 g commercial magnesium ethylate were suspended in 450 ml methanol. To this suspension, 50 ml methanol containing 8.0 g anhydrous HF (aHF) were added under rigorous stirring. No clear sol was obtained instead a non-transparent suspension of large MgF.sub.2 particles was formed which did not clear up even after several weeks stirring.
C) 17.1 g commercial magnesium ethylate were suspended in 450 ml ethanol. To this suspension, 50 ml ethanol containing 6.0 g anhydrous HF (aHF) were added under rigorous stirring. No clear sol was obtained instead a non-transparent suspension of large MgF.sub.2 particles was formed which did not clear up even after several weeks stirring and did not give transparent coatings on glass.
Formation of MgF.sub.2-AR-Layers on Glass Substrates

(13) The general procedure of producing AR-layers based on sols obtained according the procedures described under 1) to 4) followed the following general protocol. Optiwhite glass substrates (Pilkington, Gelsenkirchen, Germany) of 100150 mm were dip-coated with the respective MgF.sub.2-sol. Before dip coating the substrates were cleaned with an alkaline cleaning solution and finally neutralized by washing with de-ionized water. After a drying step at 80 C. for 10 min all samples were finally annealed at 450 C. for 15 min. For this, the samples were heated by 5 C. per minute up to 450, kept there for 15 min and then with the same heatingprogramm cooled down.

(14) Formation of AR-Layers on Polymer Surfaces

(15) The durability of the MgF.sub.2 sols obtained according the procedures 1) to 4) was performed by dip-coating technique. Plates/foils of several polymers (polyethylene terephthalate (PET), fluorinated ethylene polypropylene (FEP), polyethersulfone (PES), polycarbonate (PC), ethylene tetrafluoroethylene (ETFE), polymethylmethacrylate (PMMA), PC Lexan (amorphous polycarbonate polymer), Zeonex (cyclic olefin polymer, CAS No 26007-43-2), Makrolon (polycarbonate)) were generally first cleaned by treating them with different organic solvents and then either directly coated without any further treatment or Corona pre-treated or in some cases, a mediator layer made from either Ormosil@ or Silazanes was first deposited in order to improve the grafting properties.

(16) Characterization of the MgF.sub.2-Sols

(17) The hydrodynamic diameter of the nano particles was determined by dynamic light scattering (DLS) measurements using a Zetasizer Nano ZS (Malvern Instruments, Worcestershire, UK) using quartz cuvettes flushed with an argon atmosphere. The viscosity was determined simultaneous to DLS measurements with a microviscometer from Anton Paar (AMVn; Graz, Austria) at 25 C. Hydrodynamic diameter were calculated by deconvolution of the correlation functions into exponential functions using non-negatively constrained least squares (NNLS) fitting algorithm as implemented in the Malvern Nanosizer software. The zeta potential was determined from the electrophoretic mobilities of the particles in the sol using the Smoluchowski relation.

(18) Characterization of the MgF.sub.2-AR-Layers

(19) The refractive indices and the optical transmission and reflectance, respectively, were determined by ellipsometric measurements with a variable angle UV-V is spectroscopic ellipsometer SE850 of the company SENTECH Instruments GmbH in the wavelength range between 350 nm and 1000 nm. For the evaluation and fitting of the refraction indices n and the absorption k were used the data set in the visible range (350-800 nm) using the CAUCHY model. The reported refractive indices were taken at a wavelength of 589 nm.

(20) The mechanical stability of the AR-layers was tested according the pencil test using a Linartester 249 from ERICHSEN GmbH & Co KG, Germany. In this test, pencil leads of increasing hardness values are forced against a coated surface in a precisely defined manner until one lead mars the surface. Surface hardness is defined by the hardest pencil grade which just fails to mar the painted surface.

(21) .sup.19F MAS NMR spectra were recorded on a Bruker Avance 400. The chemical shifts of the nuclei are given with respect to CFCl.sub.3 for .sup.19F.

(22) XRD measurements were performed with the FPM7 equipment (Rich. Seiffert & Co., Freiberg) with Cu K (Cu K1.2, =1.542 ) radiation (2 range: 5264).

(23) All the sols described under 1) to 18) gave AR-layers which do not differ remarkably from each other based on simple eye inspection. The characteristic data of the MgF.sub.2Ar-layers made are summarized in Table 5.

(24) Table 5 summarizes the main characteristics of Ar-layers on Optiwhite glass

(25) TABLE-US-00005 Layer thicknes Refractive sindex Sample [nm] n.sub.550 Pencil -Test .sup.(1) 117 1.2747 6 H .sup.(3) 121 1.24 6 H-7 H .sup.(3a) 125 1.27 7 H .sup.(3*b) 120 1.29 9 H .sup.(3c) 121 1.31 9 H .sup.(4) 107 1.27 3 H-4 H .sup.(4) 107 1.27 3 H-4 H 8a 116 1.26 3 H-4 h 8b 123 1.25 4 H-5 H 8c 119 1.26 4 H-5 H 11 121 1.24 6 H-7 H 12 110 1.28 3 H 13 109 1.29 4 H 14 105 1.26 9 H 15 112 1.27 4 H 16 109 1.25 6 H 17 110 1.24 8 H 18 112 124 8 H