LED SYSTEM

Abstract

A non-hermetically sealed LED system containing an active composition having an amount between 0.06 and 2.5 mg per cm.sup.2 of the system optical window area is described. The active composition contains an active material in powder form, wherein at least 75 wt % of the active material is chosen from one or more of active carbons, silver, copper, zinc, copper oxide, zinc oxide, calcium oxide, and silver oxide.

Claims

1. An LED system having an optical window and an internal volume non-hermetically sealed wherein the H.sub.2S ingress in said internal volume is comprised between 5,5*10.sup.−4 and 1,9*10.sup.−1 micrograms/day when the H.sub.2S external volume concentration is 10 ppb, and containing in said internal volume an active composition having an amount comprised between 0,06 and 2,5 mg per cm.sup.2 of the system optical window area, said active composition containing an active material in powder form, wherein at least 75 wt % of said active material is chosen from one or more of active carbons, silver, copper, zinc, copper oxide, zinc oxide, calcium oxide, silver oxide.

2. The LED system according to claim 1, wherein said active material powders have an average size comprised between 0,1 and 20 μm.

3. The LED system according to claim 1, wherein said active composition contains at least an additional active material chosen from cerium oxide, palladium oxide, tin oxide, iron oxide, manganese oxide, in an amount comprised between 1 and 25 wt %.

4. The LED system according to claim 1, wherein said active composition amount per cm.sup.2 of the optical window area is comprised between 0,1 and 1 mg.

5. The LED system according to claim 1, wherein said active materials are in the form of powders with a specific surface ≧70 m.sup.2/g.

6. The LED system according to claim 1, wherein said active material powders are retained in a suitable container.

7. The LED system according to claim 1, wherein said active material powders are compressed in the form of stand-alone pills or tablets.

8. The LED system according to claim 1, wherein said active material powders are dispersed in a polymeric matrix, said matrix being preferably based on a silicone- or silicone-epoxy- or silicone-acrylic-based resin.

9. The LED system according to claim 8, wherein said polymeric matrix containing the active material powders is deposited on a supporting strip, preferably a metallic strip.

10. The LED system according to claim 8, wherein said active material powders concentration in the active composition is comprised between 0,1 wt % and 12 wt %, preferably between 1,5 wt % and 8 wt %.

11. The LED system according to claim 10, wherein said active composition is placed over a LED die for its encapsulation.

Description

EXAMPLE 1a

Sample Preparation

[0034] Several samples are prepared applying a silver layer or a silver coating on stainless steel substrates, each substrate having a surface of 12,5 cm.sup.2. The average thickness of the applied silver layer or coating is 5 μm and the coverage is unitary. Measured reported values are averaged on several sample points. The weight of deposited silver is calculated as weight difference between the substrate before and after deposition and consolidation, corrected for the residue of the matrix.

[0035] Comparative sample C1 consists of a silver foil glued on a substrate of stainless steel; the specific load of silver on the sample is 5,2 mg/cm.sup.2, it represents the solution described in the above referenced US patent application 2014/168526, as such amount correspond to a silver layer with a 10 micron thickness, over half of the substrate surface.

[0036] Other samples are prepared using a silver paste, consisting of a combination of small Ag particles, adhesive agent and dispersant, deposited by doctor blading with thickness of about 5 μm and consolidated in air at 250° C. for 90 minutes; by varying the relative amounts of these components different samples with final average specific load of silver are made, more specifically, comparative sample C2 with 2,9 mg/cm.sup.2 and sample S1 with 2,0 mg/cm.sup.2.

[0037] Further samples are prepared with lower silver content, by depositing by doctor blading and consolidating in air at 250° C. for 90 minutes a paste of silver powder mixed with a gas permeable silicone-based resin and a volatile solvent; by varying the relative amounts of these components, different samples with final average specific load of silver are made, more specifically, sample S2 with 0,8 mg/cm.sup.2, sample S3 with 0,5 mg/cm.sup.2, sample S4 with 0,08 mg/cm.sup.2 and finally sample C3 with 0,005 mg/cm.sup.2.

EXAMPLE 1b

Sample Characterization

[0038] The prepared samples have been evaluated in terms of relative performance, concerning sorption capacity for sulfur, as Function of the specific Ag load. Sulfur is delivered in a chamber of about 1 liter containing all the samples by means of a flux of H.sub.2S, at the concentration of 4 ppm in a nitrogen carrier with a 220 cc/min flow. All samples have been exposed under the same conditions for the same time of 15 hours.

[0039] The obtained results are shown in table 1, reporting the sample ID, the average silver load, and the relative amount of S atoms with respect to Ag ones measured on the samples by a calibrated Energy-Dispersive X-ray (EDX) probe, indicating therefore the different samples efficiencies.

TABLE-US-00001 TABLE 1 Sample Average Ag S atoms/Ag ID load (mg/cm.sup.2) atoms (%) C1 5.2 0.1 C2 2.9 0.8 S1 2.0 1.2 S2 0.8 9.4 S3 0.5 2.2 S4 0.08 1.1 C3 0.005 <0.1

[0040] It is possible to observe that only with the samples according to the present invention there is an efficiency higher than 1%, being for the best sample (S2) almost two orders of magnitude higher than the one achieved with sample C1, made according to US patent application 2014/168526. The lower limit is identified in terms of efficiency: the 1% S/Ag atom ratio is considered as a suitable value to assure that the adopted solution, also in view of the specified constraint on the optical window area, not only is capable to remove a certain amount of S, but also with an acceptable kinetic, as evidenced by the S load achieved and measured after the experiment duration of 15 hours.

EXAMPLE 2a

Sample Preparation

[0041] This example makes a comparison among two embodiments according to the present invention; in particular sample S5 is prepared with the same method as S2 but with a paste containing, instead of the Ag powder, a powder mixture of calcium oxide (90% wt) and iron oxide (10% wt), Sample S5 has an active composition load of 0,3 mg/cm.sup.2 and a coating thickness of 5 μm.

EXAMPLE 2b

Sample Characterization

[0042] Similarly to example 1b, the prepared samples have been evaluated in terms of relative performance, concerning sorption capacity for sulfur expressed as relative amount of S atoms with respect to atoms of the active composition (Ag atoms for S2, Ca+Fe atoms For S5). Results are reported in table 2.

TABLE-US-00002 TABLE 2 Average active Sample composition load S atoms/active ID (mg/cm.sup.2) atom (%) S2 0.8 9.4 S5 0.3 14

[0043] As shown in table 2, both samples S2 and S5 have capabilities well above the 1% (S atoms)/(active composition atoms) ratio; even though S5 has a lower active composition load, such sample is even capable to achieve a higher efficiency, so this specific solution (calcium oxide and iron oxide combination) is a preferred embodiment according to the present invention.