Illuminant mixture for a discharge lamp and discharge lamp, in particular an Hg low-pressure discharge lamp

1. A phosphor mixture for a discharge lamp which comprises:

(a) a first phosphor composition having an emission spectrum in the green and/or yellow spectral range, and comprises (i) a first phosphor compound which is free of Tb and is capable to absorb the UV radiation emitted by an Hg source and has an orthosilicate of the formula (Ba,Sr,Ca) 2 SiO 4 :Eu or an oxynitride of the formula (Sr 1-x-y Ba x Ca y )Si 2 O 2 N 2 :Eu (SrSiON), and (ii) at least one second phosphor compound which contains Tb, and which is selected from the group consisting of (Ce,Tb)MgAl 11 O 19 and (La,Ce,Tb)PO 4 ,

wherein a mass fraction of the second phosphor compound is less than a mass fraction of the first phosphor compound, and

(b) a second phosphor composition having an emission spectrum in the red spectral range and comprises Y 2 O 3 :Eu.

2. The phosphor mixture as claimed in claim 1 , wherein the first phosphor compound of the first phosphor composition is capable to convert the absorbed UV radiation into its emission spectrum.

3. The phosphor mixture as claimed in claim 1 , wherein the color temperature of the emitted radiation is operable to be set as a function of an adjustable mass ratio between the first and second phosphor compositions.

4. The phosphor mixture as claimed in claim 3 , wherein a mass fraction of the first phosphor composition is less than or equal to 50% of the compound mixture.

5. The phosphor mixture as claimed in claim 3 , wherein the color temperature is more than 2500 K.

6. The phosphor mixture as claimed in claim 1 , wherein the first phosphor compound of the first phosphor composition has a strong absorption for radiation with wavelengths of less than 440 nm.

7. The phosphor mixture as claimed in claim 6 , wherein the first phosphor compound of the first phosphor composition has a very strong absorption for radiation with wavelengths of about 254 nm.

8. The phosphor mixture as claimed in claim 7 , wherein the first phosphor compound of the first phosphor composition has a weak absorption for radiation with wavelengths of more than 530 nm.

9. The phosphor mixture as claimed in claim 1 , wherein the emission spectrum of the first phosphor compound of the first phosphor composition has a dominant wavelength of between 530 nm and 570 nm.

10. The phosphor mixture as claimed in claim 1 , wherein the width at half maximum of the emission band of the first phosphor compound of the first phosphor composition is less than 100 nm.

11. The phosphor mixture as claimed in claim 1 , wherein the first phosphor compound of the first phosphor composition is doped with Eu, and a mass fraction of the Eu doping lies between 0.1% and 15%.

12. The phosphor mixture as claimed in claim 11 , wherein the mass fraction of the Eu doping lies between 1% and 2%.

13. A phosphor mixture for a discharge lamp which comprises:

(a) a first phosphor composition having an emission spectrum in the green and/or yellow spectral range, and comprises (i) a first phosphor compound which is free of Tb and is capable to absorb the UV radiation emitted by an Hg source and has an orthosilicate of the formula (Ba,Sr,Ca) 2 SiO 4 :Eu or an oxynitride of the formula (Sr 1-x-y Ba x Ca y )Si 2 O 2 N 2 :Eu (SrSiON), and (ii) at least one second phosphor compound which contains Tb, and which is selected from the group consisting of (Ce,Tb)MgAl 11 O 19 and (La,Ce,Tb)PO 4 ,

wherein a mass fraction of the second phosphor compound is less than a mass fraction of the first phosphor compound;

(b) a second phosphor composition having an emission spectrum in the red spectral range and comprises Y 2 O 3 :Eu; and

(C) a third phosphor composition having an emission spectrum in the blue spectral range,

wherein the third phosphor composition has a phosphor compound which comprises (Ba,Eu)MgAl 10 O 17 or (Sr,Ba,Ca,Mg,Eu) 5 (PO 4 ) 3 (F,Cl) as constituents, and wherein the phosphor compound of the third phosphor composition is doped with Eu.

14. A phosphor mixture for a discharge lamp which comprises:

(a) a first phosphor composition having an emission spectrum in the green and/or yellow spectral range, and comprises (i) a first phosphor compound which is free of Tb and is capable to absorb the UV radiation emitted by an Hg source and has an orthosilicate of the formula (Ba,Sr,Ca) 2 SiO 4 :Eu or an oxynitride of the formula (Sr 1-x-y Ba x Ca y ) Si 2 O 2 N 2 :Eu(SrSiON), and (ii) at least one second phosphor compound which contains Tb, and which is selected from the group consisting of (Ce,Tb)MgAl 11 O 19 and (La,Ce,Tb)PO 4 ,

wherein a mass fraction of the second phosphor compound is less than a mass fraction of the first phosphor compound;

(b) a second phosphor composition having an emission spectrum in the red spectral range and comprises Y 2 O 3 :Eu; and

(c) a fourth phosphor composition having an emission spectrum in the blue-green spectral range, wherein the fourth phosphor composition has a phosphor compound which comprises (Ba,Eu) (Mg,Mn)Al 10 O 17 as a constituent, and wherein the phosphor compound of the fourth phosphor composition is doped with Eu.

15. A discharge lamp comprising a discharge vessel on which a phosphor layer is formed, wherein at least a first phosphor layer is formed which comprises the phosphor mixture as claimed in claim 1 .

16. The discharge lamp as claimed in claim 15 , wherein the first phosphor layer is disposed directly on an inner side of the discharge vessel.

17. The discharge lamp as claimed in claim 16 , which further comprises a second phosphor layer, which comprises Tb, and is disposed on an upper side of the first phosphor layer facing away from the inner side of the discharge vessel.

18. The discharge lamp as claimed in claim 17 , wherein the second phosphor layer comprises a mixture of (Ce,Tb)MgAl 11 O 19 and Y 2 O 3 :Eu.

19. The discharge lamp as claimed in claim 16 , which further comprises a protective layer, such that the first phosphor compound of the first phosphor composition of the first phosphor layer is enclosed by the protective layer.

20. The discharge lamp as claimed in claim 19 , wherein material components of the protective layer are different from the first phosphor compound of the first phosphor composition.

21. The discharge lamp as claimed in claim 19 , wherein the protective layer comprises metal oxides.

22. The discharge lamp as claimed in claim 19 , wherein the protective layer comprises borates and/or phosphates.

23. The discharge lamp as claimed in claim 19 , wherein the protective layer comprises SiO 2 .

24. The discharge lamp as claimed in claim 15 , which further comprises at least one Hg diffusion protection layer, which is disposed between the first phosphor layer and the inner side of the discharge vessel.

25. The discharge lamp as claimed in claim 15 , which further comprises a protective layer for protecting the first phosphor compound against VUV radiation and/or a reaction with Hg ions, which is disposed on an upper side of the first phosphor layer facing away from an inner side of the discharge vessel.

26. The discharge lamp as claimed in claim 25 , wherein the protective layer comprises Al 2 O 3 and/or Y 2 O 3 .

27. The discharge lamp as claimed in claim 15 , which is a low-pressure Hg discharge lamp.

28. A phosphor mixture for a discharge lamp which comprises:

(a) a first phosphor composition having an emission spectrum in the green and/or yellow spectral range, and comprises (i) a first phosphor compound which is free of Tb and is capable to absorb the UV radiation emitted by an Hg source and has an orthosilicate of the formula (Ba,Sr,Ca) 2 SiO 4 :Eu or an oxynitride of the formula (Sr 1-x-y Ba x Ca y )Si 2 O 2 N 2 :

Eu(SrSiON), and (ii) at least one second phosphor compound which contains Tb, and which is selected from the group consisting of (Ce,Tb)MgAl 11 O 19 and (La,Ce,Tb)PO 4 , 4 ,

wherein a mass fraction of the second phosphor compound is less than a mass fraction of the first phosphor compound;

(b) a second phosphor composition having an emission spectrum in the red spectral range and comprises Y 2 O 3 :Eu;

(c) a third phosphor composition having an emission spectrum in the blue spectral range; and

(d) a fourth phosphor composition having an emission spectrum in the blue-green spectral range, wherein the fourth phosphor composition has a phosphor compound which comprises (Ba,Eu)(Mg,Mn)Al 10 O 17 as a constituent, and the phosphor compound of the fourth composition is doped with Eu.

29. The phosphor mixture as claimed in claim 28 , wherein the third phosphor composition has a phosphor compound which comprises (Ba,Eu)(Mg,Mn)Al 10 O 17 or (Sr,Ba,Ca,Mg,Eu) 5 (PO 4 ) 3 (F,Cl), and wherein the phosphor compound of the third phosphor composition is doped with Eu.