SILICATE PHOSPHORS

Abstract

The invention relates to pyrosilicate phosphors comprising a coating of aluminum oxide, to a process for the preparation of these compounds, and to the use thereof as conversion phosphors or in lamps.

Claims

1. Compound of the formula (1),
(Ba.sub.2abcdM.sub.aA.sub.bRE.sub.cD.sub.d)(Mg.sub.1efgjM.sub.eA.sub.fRE.sub.gC.sub.j)(Si.sub.2hiB.sub.hC.sub.i)(O.sub.7+mklX.sub.kN.sub.l) Formula (1) where the following applies to the symbols and indices used: M is selected from the group consisting of Ca, Sr, Zn or mixtures of these elements; A is selected from the group consisting of Na, K, Rb or mixtures of these elements; RE is selected from the group consisting of La, Y, Gd or mixtures of these elements; D is selected from the group consisting of Eu.sup.2+, Mn.sup.2+, Yb.sup.2+, Sm.sup.2+ or mixtures of these elements; M is selected from the group consisting of Zr, Hf or mixtures of these elements; A is selected from the group consisting of Li, Na or mixtures of these elements; RE is selected from the group consisting of Sc, Lu or mixtures of these elements; C is selected from the group consisting of B, Al, Ga, In or mixtures of these elements; B is selected from the group consisting of Ge, Sn or mixtures of these elements; C is selected from the group consisting of B, Al, Ga, In or mixtures of these elements; X is selected from the group consisting of F, Cl or mixtures of these elements; N is nitrogen; 0a1.0; 0b0.6; 0c0.6; 0<d2; 0e0.3; 0f0.3; 0g0.3; 0j0.6; h1.0; 0i0.6; 0k2.1; 0l2.1; 2.0m2.0; characterized in that the compound contains a coating of aluminum oxide (alumina) which has been deposited by an ALD process.

2. Compound according to claim 1, wherein the following applies for the indices used: 0a0.4; b0.2; 0c0.2; 0.01d0.2; e0.1; 0f0.1; g0.1; 0j0.2; 0h0.4; 0i0.2; k0.7; 10.7; 0.5m0.5.

3. Compound according to claim 1, characterised in that a maximum of three of the indices a, b, c, e, f, g, j, h, l, k and l is 0.

4. Compound according to claim 1, selected from the compounds of formula (2),
(Ba.sub.2abcdM.sub.aK.sub.bLa.sub.cEu.sub.d)(Mg.sub.1efgjZr.sub.eLi.sub.fSc.sub.gC.sub.j)(Si.sub.2hiGe.sub.hC.sub.i)(O.sub.7+mklX.sub.kN.sub.l) Formula (2) where the following applies for the symbols and indices used: M is selected from the group consisting of Ca, Sr or mixtures of these elements; C is selected from the group consisting of Al, Ga or mixtures of these elements; C is selected from the group consisting of Al, Ga or mixtures of these elements; X is selected from the group consisting of F, Cl or mixtures of these elements; N is nitrogen; 0a0.4; 0b0.2; 0c0.2; 0d0.4, more preferably 0.01d0.2; 0e0.1; 0f0.1; 0g0.1; 0j0.2; 0h0.4; 0i0.2; 0k0.7; 010.7; 0.5m0.5.

5. Compound according to claim 1, selected from the compounds of formulae (3) to (17),
(Ba.sub.2bdA.sub.bD.sub.d)Mg Si.sub.2(O.sub.7bX.sub.b)(3)
(Ba.sub.2bdA.sub.bD.sub.d)(Mg.sub.1bRE.sub.b)Si.sub.2O.sub.7(4)
(Ba.sub.2bdA.sub.bD.sub.d)Mg Si.sub.2O.sub.70.5b(5)
(Ba.sub.2cdRE.sub.cD.sub.d)Mg Si.sub.2(O.sub.7cN.sub.c)(6)
(Ba.sub.2dD.sub.d)(Mg.sub.1gRE.sub.g)Si.sub.2(O.sub.7gN.sub.g)(7)
(Ba.sub.2dD.sub.d)(Mg.sub.1eM.sub.e)Si.sub.2O.sub.7+e(8)
(Ba.sub.2d0.5eD.sub.d)(Mg.sub.1eM.sub.e)Si.sub.2O.sub.7+0.5e(9)
(Ba.sub.2dD.sub.d)(Mg.sub.1fA.sub.f)Si.sub.2(O.sub.7fX.sub.f)(10)
(Ba.sub.2dD.sub.d)(Mg.sub.1-2fA.sub.fC.sub.f)Si.sub.2O.sub.7(11)
(Ba.sub.2dD.sub.d)(Mg.sub.1fA.sub.f)(Si.sub.2fC.sub.f)O.sub.7(12)
(Ba.sub.2dD.sub.d)(Mg.sub.12eM.sub.eRE.sub.e)Si.sub.2(O.sub.7eN.sub.e)(13)
(Ba.sub.2dD.sub.d)Mg Si.sub.2O.sub.7(14)
(Ba.sub.2adM.sub.aD.sub.d)Mg Si.sub.2O.sub.7(15)
(Ba.sub.2dD.sub.d)Mg(Si.sub.2hB.sub.b)O.sub.7(16)
(Ba.sub.2dD.sub.d)(Mg.sub.1jC.sub.j)(Si.sub.2jC.sub.j)O.sub.7(17) where the symbols and indices have the meanings given above and furthermore: b0 in formula (3), (4) and (5), c0 in formula (6), g0 in formula (7), e0 in formula (8) and (9), f0 in formula (10), (11) and (12), and e0 in formula (13).

6. Compound according to claim 1, selected from the compounds of formulae (3a) to (17a),
(Ba.sub.2bdK.sub.bEu.sub.d)Mg Si.sub.2(O.sub.7bF.sub.b)(3a)
(Ba.sub.2bdK.sub.bEu.sub.d)Mg Si.sub.2(O.sub.7bCl.sub.b)(3b)
(Ba.sub.2bdK.sub.bEu.sub.d)(Mg.sub.1bSc.sub.b)Si.sub.2O.sub.7(4a)
(Ba.sub.2bdK.sub.bEu.sub.d)Mg Si.sub.2O.sub.70.5b(5a)
(Ba.sub.2cdLa.sub.cEu.sub.d)Mg Si.sub.2(O.sub.7cN.sub.c)(6a)
(Ba.sub.2dEu.sub.d)(Mg.sub.1gSc.sub.g)Si.sub.2(O.sub.7gN.sub.g)(7a)
(Ba.sub.2dEu.sub.d)(Mg.sub.1eZr.sub.e)Si.sub.2O.sub.7+e(8a)
(Ba.sub.2d0.5eEu.sub.d)(Mg.sub.1eZr.sub.e)Si.sub.2O.sub.7+0.5e(9a)
(Ba.sub.2dEu.sub.d)(Mg.sub.1fLi.sub.f)Si.sub.2(O.sub.7fF.sub.f)(10a)
(Ba.sub.2dEu.sub.d)(Mg.sub.1fLi.sub.f)Si.sub.2(O.sub.7fCl.sub.f)(10b)
(Ba.sub.2dEu.sub.d)(Mg.sub.12fLi.sub.fAl.sub.f)Si.sub.2O.sub.7(11a)
(Ba.sub.2dEu.sub.d)(Mg.sub.12fLi.sub.fGa.sub.f)Si.sub.2O.sub.7(11b)
(Ba.sub.2dEu.sub.d)(Mg.sub.1fLi.sub.f)(Si.sub.2fAl.sub.f)O.sub.7(12a)
(Ba.sub.2dEu.sub.d)(Mg.sub.1fLi.sub.f)(Si.sub.2fGa.sub.f)O.sub.7(12b)
(Ba.sub.2dEu.sub.d)(Mg.sub.12eZr.sub.eSc.sub.e)Si.sub.2(O.sub.7eN.sub.e)(13a)
(Ba.sub.1dEu.sub.d).sub.2Mg Si.sub.2O.sub.7(14a)
(Ba.sub.1adSr.sub.aEu.sub.d).sub.2Mg Si.sub.2O.sub.7(15a)
(Ba.sub.1adCa.sub.aEu.sub.d).sub.2Mg Si.sub.2O.sub.7(15b)
(Ba.sub.1dEu.sub.d).sub.2Mg(Si.sub.1hGe.sub.h).sub.2O.sub.7(16a)
(Ba.sub.2dEu.sub.d)(Mg.sub.1jAl.sub.j)(Si.sub.2jAl.sub.j)O.sub.7(17a) where the symbols and indices have the meanings given above and furthermore: b0 in formula (3a), (3b), (4a) and (5a), c0 in formula (6a), g0 in formula (7a), e0 in formula (8a) and (9a), f0 in formula (10a), (10b), (11a), (11b), (12a) and (12b), and e0 in formula (13a).

7. Compound according to claim 1 wherein the coating has a thickness between 0.5 and 150 nm, preferably between 2 and 75 nm and in particular between 3 and 50 nm.

8. Method for the preparation of a phosphor according to claim 1, comprising the following process steps: a) provision of a compound of formula (1); and b) forming a layer of aluminum oxide on the surface of the compound via an atomic layer deposition process.

9. Method according to claim 8, wherein the formation of the layer of aluminum oxide comprises the following steps: b1) introduction of a purge/fluidizing gas; b2) introduction of a mixture of carrier gas and first reagent; b3) introduction of a purge/fluidizing gas and/or pull a vacuum to remove excess quantities of the first reagent as well as reaction by-products; b4) introduction of a mixture of carrier gas and second reagent; b5) introduction of a purge/fluidizing gas and/or pull a vacuum to remove excess quantities of the second reagent and reaction by-products; b6) repeat steps b2) to b5) until desired coating thickness is obtained.

10. Method according to claim 9 wherein argon, nitrogen, other inert gas, or mixture of inert gases is used as the purge/fluidizing gas and argon, nitrogen, other inert gas, or mixture of inert gases is used as carrier gas.

11. Method according to claim 9 wherein trialkyl aluminum, in particular trimethyl aluminum or triethyl aluminum, or an aluminum trihalide, in particular aluminum trichloride, are used as the first reagent and an oxidizer, preferably selected from water, oxygen plasma species, ozone or alcohols is used as the second reagent.

12. A method comprising partial or complete conversion of the near-UV emission or violet emission of a light-emitting diode into light having a longer wavelength by a conversion phosphor comprising a compound according to claim 1.

13. Light source which comprises at least one primary light source and at least one compound according to claim 1.

14. Light source according to claim 13, wherein the primary light source is a luminescent indium aluminium gallium nitride, or a luminescent arrangement based on ZnO, TCO (transparent conducting oxide) or SiC, or a near-UV or violet laser, or a source which exhibits electroluminescence and/or photoluminescence, or a plasma or discharge source.

15. Lighting unit, in particular for the backlighting of display devices, characterised in that it comprises at least one light source according to claim 13.

Description

EXAMPLES

[0158] The enhanced stability of ALD-treated pyrosilicate phosphors is shown by the examples as follows:

Example 1: Synthesis of Ba.SUB.1.90.Eu.SUB.0.10.MgSi.SUB.2.O.SUB.7

112.49 g BaCO.SUB.3

[0159] 29.14 g Mg.sub.5(CO.sub.3).sub.4(OH).sub.2
5.28 g Eu.sub.2O.sub.3

37.20 g SiO.SUB.2

1.60 g NH.SUB.4.Cl

[0160] The starting materials are mixed by ball milling for 2 hours and fired at 1100 C. for 6 h in an H.sub.2:N.sub.2 (70:30) atmosphere. After firing, the material is ground into a fine powder, washed in water, dried and sieved using a 50 m nylon sieve to narrow the particle size range. The resulting compound shows an emission maximum at 512 nm (x=0.252; y=0.514).

Example 2: Synthesis of Ba.SUB.1.85.K.SUB.0.05.Eu.SUB.0.10.MgSi.SUB.2.O.SUB.6.95.Cl.SUB.0.05

14.60 g BaCO.SUB.3

[0161] 0.15 g K.sub.2CO.sub.30.5H.sub.2O
3.89 g Mg.sub.5(CO.sub.3).sub.4(OH).sub.2
0.70 g Eu.sub.2O.sub.3

4.96 g SiO.SUB.2

0.21 g NH.SUB.4.Cl

[0162] The starting materials are mixed in a mechanical mortar for 20 minutes and fired at 1100 C. for 6 h in an H.sub.2:N.sub.2 (70:30) atmosphere. After firing, the material is ground into a fine powder, washed in water, dried and sieved using a 50 m nylon sieve to narrow the particle size range. The resulting compound shows an emission maximum at 518 nm (x=0.273; y=0.521).

Example 3: Synthesis of Ba.SUB.1.85.K.SUB.0.05.Eu.SUB.0.10.MgSi.SUB.2.O.SUB.6.95.F.SUB.0.05

14.60 g BaCO.SUB.3

0.12 g KF

[0163] 3.89 g Mg.sub.5(CO.sub.3).sub.4(OH).sub.2
0.70 g Eu.sub.2O.sub.3

4.96 g SiO.SUB.2

0.21 g NH.SUB.4.Cl

[0164] The starting materials are mixed in a mechanical mortar for 20 minutes and fired at 1100 C. for 6 h in an H.sub.2:N.sub.2 (70:30) atmosphere. After firing, the material is ground into a fine powder, washed in water, dried and sieved using a 50 m nylon sieve to narrow the particle size range. The resulting compound shows an emission maximum at 516 nm (x=0.260; y=0.520).

Example 4: Synthesis of Ba.SUB.1.90.Eu.SUB.0.10.Mg.SUB.0.95.Li.SUB.0.05.Si.SUB.2.O.SUB.6.95.Cl.SUB.0.05

15.00 g BaCO.SUB.3

[0165] 0.07 g Li.sub.2CO.sub.3
3.69 g Mg.sub.5(CO.sub.3).sub.4(OH).sub.2
0.70 g Eu.sub.2O.sub.3

4.96 g SiO.SUB.2

0.21 g NH.SUB.4.Cl

[0166] The starting materials are mixed in a mechanical mortar for 20 minutes and fired at 1100 C. for 6 h in an H.sub.2:N.sub.2 (70:30) atmosphere. After firing, the material is ground into a fine powder, washed in water, dried and sieved using a 50 m nylon sieve to narrow the particle size range. The resulting compound shows an emission maximum at 513 nm (x=0.253; y=0.517).

Example 5: Synthesis of Ba.SUB.1.90.Eu.SUB.0.10.Mg.SUB.0.95.Li.SUB.0.05.Si.SUB.2.O.SUB.6.95.F.SUB.0.05

15.00 g BaCO.SUB.3

[0167] 0.07 g Li.sub.2CO.sub.3
3.69 g Mg.sub.5(CO.sub.3).sub.4(OH).sub.2
0.70 g Eu.sub.2O.sub.3

4.96 g SiO.SUB.2

0.21 g NH.SUB.4.Cl

0.21 g BaF.SUB.2

[0168] The starting materials are mixed in a mechanical mortar for 20 minutes and fired at 1100 C. for 6 h in an H.sub.2:N.sub.2 (70:30) atmosphere. After firing, the material is ground into a fine powder, washed in water, dried and sieved using a 50 m nylon sieve to narrow the particle size range. The resulting compound shows an emission maximum at 518 nm (x=0.272; y=0.528).

Example 6: Synthesis of Ba.SUB.1.90.Eu.SUB.0.10.Mg.SUB.0.80.Li.SUB.0.1.Al.SUB.0.1.Si.SUB.2.O.SUB.7

15.00 g BaCO.SUB.3

[0169] 0.15 g Li.sub.2CO.sub.3
3.11 g Mg.sub.5(CO.sub.3).sub.4(OH).sub.2
0.70 g Eu.sub.2O.sub.3

4.96 g SiO.SUB.2

0.21 g NH.SUB.4.Cl

[0170] 0.20 g Al.sub.2O.sub.3

[0171] The starting materials are mixed in a mechanical mortar for 20 minutes and fired at 1100 C. for 6 h in an H.sub.2:N.sub.2 (70:30) atmosphere. After firing, the material is ground into a fine powder, washed in water, dried and sieved using a 50 m nylon sieve to narrow the particle size range. The resulting compound shows an emission maximum at 521 nm (x=0.289; y=0.527).

Example 7: Synthesis of Ba.SUB.1.90.Eu.SUB.0.10.Mg.SUB.0.95.Zr.SUB.0.05.Si.SUB.2.O.SUB.7.05

15.00 g BaCO.SUB.3

[0172] 3.69 g Mg.sub.5(CO.sub.3).sub.4(OH).sub.2
0.70 g Eu.sub.2O.sub.3

4.96 g SiO.SUB.2

0.21 g NH.SUB.4.Cl

0.25 g ZrO.SUB.2

[0173] The starting materials are mixed in a mechanical mortar for 20 minutes and fired at 1100 C. for 6 h in an H.sub.2:N.sub.2 (70:30) atmosphere. After firing, the material is ground into a fine powder, washed in water, dried and sieved using a 50 m nylon sieve to narrow the particle size range. The resulting compound shows an emission maximum at 516 nm (x=0.260; y=0.515).

Example 8: Synthesis of Ba.SUB.1.90.Eu.SUB.0.10.Mg.SUB.0.95.Sc.SUB.0.05.Si.SUB.2.O.SUB.7.025

7.499 g BaCO.SUB.3

[0174] 1.845 g Mg.sub.5(CO.sub.3).sub.4(OH).sub.2
0.352 g Eu.sub.2O.sub.3

2.463 g SiO.SUB.2

0.107 g NH.SUB.4.Cl

[0175] 0.069 g Sc.sub.2O.sub.3

[0176] The starting materials are mixed in a mechanical mortar for 20 minutes and fired at 1100 C. for 6 h in an H.sub.2:N.sub.2 (70:30) atmosphere. After firing, the material is ground into a fine powder, washed in water, dried and sieved using a 50 m nylon sieve to narrow the particle size range. The resulting compound shows an emission maximum at 512 nm (x=0.255, y=0.498).

Example 9: Synthesis of Ba.SUB.1.86.Eu.SUB.0.10.La.SUB.0.04.MgSi.SUB.2.O.SUB.7.02

11.779 g BaCO.SUB.3

[0177] 3.185 g Mg.sub.5(CO.sub.3).sub.4(OH).sub.2
0.577 g Eu.sub.2O.sub.3

4.040 g SiO.SUB.2

0.175 g NH.SUB.4.Cl

[0178] 0.214 g La.sub.2O.sub.3

[0179] The starting materials are mixed in a mechanical mortar for 20 minutes and fired at 1100 C. for 6 h in an H.sub.2:N.sub.2 (70:30) atmosphere. After firing, the material is ground into a fine powder, washed in water, dried and sieved using a 50 m nylon sieve to narrow the particle size range. The resulting compound shows an emission maximum at 512 nm (x=0.255, y=0.507).

Example 10: Comparison Between ALD-Treated Pyrosilicate of Examples 1 to 9 Stabilized by 100 Cycles Coating with Untreated Pure Pyrosilicates of Examples 1 to 9

[0180] Deposition of the Al.sub.2O.sub.3 Coating:

[0181] An ALD film was deposited on the untreated pure pyrosilicates of Examples 1 to 9 using trimethylaluminum and water vapor. One hundred (100) A-B cycles were performed at reduced pressure and 180 C. within a 500 mL stainless steel fluidized bed reactor (600 g batch). The precursors were alternately dosed between nitrogen purges, to ensure ALD reactions and not CVD. N.sub.2 is used as the carrier gas.

[0182] The results are comparable for pyrosilicate materials coated in a fluidized bed reactor and pyrosilicate materials coated in a rotary system.

Example 11: Comparative Example for Wet-Chemical Coating with Alumina

[0183] 15 g of Ba.sub.1.90Eu.sub.0.10MgSi.sub.2O.sub.7 (Example 1) pyrosilicate phosphor was dispersed in 500 cm.sup.3 of water at 80 C. under vigorous and continuous stirring. The pH of the solution was adjusted to about 7.5 with a NaOH solution. Simultaneous addition of 2.5 g of Al(NO.sub.3).sub.3*9H.sub.2O (dissolved in 100 cm.sup.3 of water) and NaOH solution followed. The amount of sodium hydroxide was adjusted such that the pH remained constant (within 0.2) at 7.5, pH required for Al(OH).sub.3 precipitation. After full addition of the aluminum nitrate solution, the phosphor was stirred for 1 h at same condition in order to age the precipitate. Filtering and washing steps followed, after which the phosphor was dried and a calcination step was applied at 350 C. for 1 h. This step is required in order to transform the aluminum hydroxide into aluminum oxide. Such prepared phosphor was used to fabricate the LEDs use for comparative studies.

Example 12: Prototype LED Fabrication

[0184] The prototype LEDs used for the LED tests are fabricated as follows: Silicone binder (OE 6370HF, Dow Corning) and phosphors according to Examples 10 and 11 or the corresponding uncoated phosphors according to Examples 1 to 9 are mixed in the weight ratio 79:21. The slurries are filled into empty LED packages of 3528 type equipped with violet dye emitting at 407 nm or 410 nm (operation at 350 mA) by means of volume dispensing by means of an automated dispensing equipment. The silicone is cured for 4 h at 150 C.

Example 13: LED Reliability Test

[0185] The prototype LEDs used for the LED reliability tests are fabricated as follows: Silicone binder (OE 6370, Dow Corning) and phosphors according to Examples 10 and 11 or the corresponding uncoated phosphors according to Examples 1 to 9 are mixed in the weight ratio 79:21. The slurries are filled into empty LED packages of 3528 type equipped with blue dye emitting at 450 nm (operation at 20 mA) by means of volume dispensing. The silicone is cured for 2 h at 150 C.

[0186] LEDs fabricated as described are introduced into a climate chamber operating at 85 C./85% rel. humidity. The LEDs are stored under these conditions for at least 1000 h and driven at 20 mA (constant operation). Within this timeframe, the devices are taken out of the climate chamber several times to characterize the chromaticity and the LED brightness by means of a spectroradiometer at 20 mA driving conditions. After completion of measurements the LEDs are reinstalled into the climate chamber.

[0187] According to E. Fred Schubert Light-Emitting Diodes, Cambridge University Press (2003) the lifetime of an LED is >>1000 hrs. The human eye can differentiate chromaticity differences of x=y0.004.

[0188] As can be seen from FIGS. 2 to 9 below, the non-stabilized pyrosilicate phosphors show a poorer reliability such as a decreased lifetime and an increased color coordinate shift when compared to pyrosilicate phosphors which were stabilized according to the present invention. Thus, it could be shown that the reliability greatly improves when the material is coated by a thin layer of alumina using the atomic layer deposition (ALD) method. Even alternative coating methods, such as e.g. sol-gel/wet chemical alumina deposition or CVD which were described in the past (e.g. H. Winkler et al. in WO 2015/062697 A1) show a worse performance when compared to the coated pyrosilicates according to the present invention. FIGS. 8 and 9 below show a comparison of different stabilization levels of pyrosilicates using ALD coating with alumina as well as wet chemical coating with alumina in terms of reliability testing monitoring the brightness change as well as the color coordinate shift (x,y shift). The data below shows that ALD coating gives the best performance improvement for pyrosilicates, while the wet chemical alumina deposition, though it improves the stability to some degree, is not sufficient. It is expected that this trend will be practically the same for co-doped pyrosilicates, (e.g. Zr.sup.4+ in place of Mg.sup.2+ as shown in FIGS. 6 and 7), since the co-doping does not fundamentally change the phosphor's sensitivity towards water and heat.

DESCRIPTION OF THE FIGURES

[0189] FIG. 1: Emission spectra of uncoated (Example 1) and rotary ALD coated system alumina-coated (Example 10) pyrosilicate Ba.sub.1.90Eu.sub.0.10MgSi.sub.2O.sub.7 under a 410 nm excitation. The intensity and emission band shape remains unchanged after deposition process.

[0190] FIG. 2: Reliability comparison (brightness) between the uncoated (Example 1) and alumina-coated (Example 10) pyrosilicate Ba.sub.1.90Eu.sub.0.10MgSi.sub.2O.sub.7 in an LED reliability test (in a standard 85 C./85% rel. humidity, storage time t=1000 h testing conditions with a 20 mA driving current): the LED intensity of the ALD treated phosphor (Example 10) remains almost unchanged; in contrast the brightness of the LED built with untreated phosphor (Example 1) decreases.

[0191] FIG. 3: Reliability comparison (CIE 1931 x co-ordinate drift) between the uncoated (Example 1) and alumina-coated (Example 10) pyrosilicate Ba.sub.1.90Eu.sub.0.10MgSi.sub.2O.sub.7 in an LED reliability test (in a standard 85 C./85% rel. humidity, storage time t=1000 h testing conditions with a 20 mA driving current):

a) CIE 1931 x coordinate drift over time;
b) CIE 1931 y coordinate drift over time.

[0192] The behavior of the LED with ALD treated phosphor remains almost unchanged. In contrast the LED built with untreated phosphor shows strong shift of color point during reliability testing.

[0193] FIG. 4: Reliability comparison (brightness) between the uncoated (Example 3) and alumina-coated (Example 10) pyrosilicate Ba.sub.1.85K.sub.0.05MgSi.sub.2O.sub.6.95F.sub.0.05:Eu.sup.2+ in an LED reliability test (in a standard 85 C./85% rel. humidity, storage time t=1000 h testing conditions with a 20 mA driving current): the LED intensity of the ALD treated phosphor (Example 10) remains almost unchanged; in contrast the brightness of the LED built with untreated phosphor (Example 3) decreases.

[0194] FIG. 5: Reliability comparison (CIE 1931 x co-ordinate drift) between the uncoated (Example 3) and alumina-coated (Example 10) pyrosilicate Ba.sub.1.85K.sub.0.05MgSi.sub.2O.sub.6.95F.sub.0.05:Eu.sup.2+ in an LED reliability test (in a standard 85 C./85% rel. humidity, storage time t=1000 h testing conditions with a 20 mA driving current):

a) CIE 1931 x coordinate drift over time;
b) CIE 1931 y coordinate drift over time.

[0195] The behavior of the LED with ALD treated phosphor remains almost unchanged. In contrast the LED built with untreated phosphor shows strong shift of color point during reliability testing.

[0196] FIG. 6: Reliability comparison (brightness) between the uncoated (Example 7) and alumina-coated (Example 10) pyrosilicate Ba.sub.1.90Mg.sub.0.95Zr.sub.0.05Si.sub.2O.sub.7.05:Eu.sup.2+ in an LED reliability test (in a standard 85 C./85% rel. humidity, storage time t=1000 h testing conditions with a 20 mA driving current): the LED intensity of the ALD treated phosphor (Example 10) remains almost unchanged; in contrast the brightness of the LED built with untreated phosphor (Example 7) decreases.

[0197] FIG. 7: Reliability comparison (CIE 1931 x co-ordinate drift) between the uncoated (Example 7) and alumina-coated (Example 10) pyrosilicate Ba.sub.1.90Mg.sub.0.95Zr.sub.0.05Si.sub.2O.sub.7.05:Eu.sup.2+ in an LED reliability test (in a standard 85 C./85% rel. humidity, storage time t=1000 h testing conditions with a 20 mA driving current):

a) CIE 1931 x coordinate drift over time;
b) CIE 1931 y coordinate drift over time.

[0198] The behavior of the LED with ALD treated phosphor remains almost unchanged. In contrast the LED built with untreated phosphor shows strong shift of color point during reliability testing.

[0199] FIG. 8: Reliability comparison (brightness) between the uncoated (Example 1), wet chemical alumina- (Example 11) and alumina-coated (Example 10) pyrosilicate Ba.sub.1.90Eu.sub.0.10MgSi.sub.2O.sub.7 in an LED reliability test (in a standard 85 C./85% rel. humidity, storage time t=1000 h testing conditions with a 20 mA driving current).

[0200] FIG. 9: Reliability comparison (CIE 1931 x co-ordinate drift) between the uncoated (Example 1), wet chemical alumina- (Example 11) and alumina-coated (Example 10) pyrosilicate Ba.sub.1.90Eu.sub.0.10MgSi.sub.2O.sub.7 in an LED reliability test (in a standard 85 C./85% rel. humidity, storage time t=1000 h testing conditions with a 20 mA driving current):

a) CIE 1931 x coordinate drift over time;
b) CIE 1931 y coordinate drift over time.