Luminescent material particles comprising a coating and lighting unit comprising such luminescent material

1. A luminescent material comprising:

a plurality of particles of an UV-luminescent material, the UV-luminescent material having a core of the UV-luminescent material, and a coating,

wherein the coating comprises a first coating layer and a second coating layer,

wherein the first coating layer is between the core and the second coating layer,

wherein the second coating layer comprises one or more alkaline earth oxides selected from the group consisting of: (Mg,Ca)O, (Ca,Sr) 3 Al 2 O 6 , (Mg,Ca,Sr)Al 2 O 4 , (Ca,Sr) 4 Al 14 O 25 , (Ca,Sr)Al 4 O 7 , (Ca,Sr)Al 12 O 19 , LaMgAl 11 O 19 , (Ba,Sr)MgAl 10 O 17 , and (Ba,Sr)Mg 3 Al 14 O 25 , and

wherein the second coating layer has extending structures.

2. The luminescent material according to claim 1 , wherein the second coating layer comprises an alkaline earth oxide having the formula:

(Mg x Ca 1-x )O,

wherein x=0.0-1.0.

3. The luminescent material according to claim 1 , wherein the second coating layer comprises MgO.

4. The luminescent material according to claim 1 , wherein the first coating layer comprises one or more materials selected from the group consisting of: Al 2 O 3 (α, γ, θ, δ-phase), Ln 2 O 3 (Ln=La, Y, Lu, or a combination thereof), LnPO 4 (Ln=La, Y, Lu, or a combination thereof), SiO 2 , Al 2 SiO 5 , Mg 2 SiO 4 , (Ca,Sr,Ba)-polyphosphate, (Mg,Ca) 2 P 2 O 7 , and ZrO 2 .

5. The luminescent material according to claim 1 , wherein the first coating layer comprises Al 2 O 3 .

6. The luminescent material according to claim 1 , wherein the UV-luminescent material comprises a luminescent material excitable by UV light of a dielectric barrier noble gas excimer discharge.

7. The luminescent material according to claim 1 , wherein the UV-luminescent material comprises one or more luminescent materials selected from the group consisting of:

K(Y 1-x Lu x ) 3 F 10 :A (A=Ce, Pr, Nd, Gd, Bi, or a combination thereof),

(Y 1-x-y La x Lu y )F 3 :A (A=Ce, Pr, Nd, Gd, or a combination thereof),

(Y 1-x-y La x Lu y )PO 4 :A (A=Ce, Pr, Nd, Gd, Bi, or a combination thereof),

(Y 1-x-y La x Lu y )BO 3 :A (A=Ce, Pr, Nd, Gd, Bi, or a combination thereof),

(Ca 1-x Sr x )Li 2 SiO 4 :PrNa,

(Ca 1-x Sr x )Li 2 SiO 4 :CeNa,

(Y 1-x-y Lu x La y )AlO 3 :A (A=Pr, Gd, or a combination thereof),

LaMgAl 11 O 19 :A (A=Ce, Pr, Nd, Gd, Bi, or a combination thereof),

(Ba,Sr) 2 SiO 4 :Pr,Na,

(Ca 1-x Sr x )Al 12 O 19 :PrNa,

(Ca 1-x Sr x ) 4 Al 24 O 25 :PrNa,

(Y 1-x-y La x Lu y ) 2 SiO 5 :A (A=Ce, Pr, Gd, Nd, Bi, or a combination thereof),

(Y 1-x-y La x L y ) 2 Si 2 O 7 :A (A=Ce, Pr, Nd, Gd, Bi, or a combination thereof),

(Y 1-x Lu x ) 3 Al 5-a Ga a O 12 :A (A=Pr, Gd, Bi, or a combination thereof),

(Ba 1-x Sr x )MgAl 10 O 17 :CeNa,

Sr 2 MgSi 2 O 7 :Pb,

Sr 2 MgSi 2 O 7 :PrNa,

BaSi 2 O 5 :Pb,

LaB 3 O 6 :A (A=Pr, Gd, Bi, or a combination thereof),

SrAl 12 O 19 :CeNa, GdMgB 5 O 10 :A (A=Ce, Pr, or a combination thereof),

CaF 2 :CeNa, LaCl 3 :A (A=Ce, Pr, Gd, or a combination thereof),

SrCl 2 :CeNa, and

SrB 4 O 7 :Eu,

wherein x, y and A are each independently selected, and x=0.0-1.0, y=0.0-1.0, and x+y≦1.

8. The luminescent material according to claim 1 , wherein the UV-luminescent material comprises YPO 4 :Bi 3+ .

9. The luminescent material according to claim 1 , having a coating thickness of the multi-layer coating in the range of 2-800 nm.

10. A lighting unit comprising a light source configured to generate UV light and the luminescent material according to claim 1 .

11. The lighting unit according to claim 10 , wherein the lighting unit comprises a dielectric barrier noble gas excimer discharge lamp as light source.

12. The luminescent material according to claim 3 , wherein the second coating layer exhibits a flake-like structure.

13. The luminescent material according to claim 1 , wherein the first coating layer comprises one or more materials selected from the group consisting of Al 2 O 3 (α, γ, θ, δ-phase), Ln 2 O 3 (Ln=La, Y, Lu, or a combination thereof), LnPO 4 (Ln=La, Y, Lu, or a combination thereof), SiO 2 , Al 2 SiO 5 , Mg 2 SiO 4 , (Ca,Sr,Ba)-polyphosphate, (Mg,Ca) 2 P 2 O 7 , or ZrO 2 , and wherein the alkaline earth oxide comprise (Mg x Ca 1-x )O, with x=0.0-1.0.