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EP-4740713-A1 - ULTRA-VIOLET RADIATION SOURCE AND METHOD FOR IDENTIFICATION OF A NECESSARY DOSE OF A FLUORESCENT MATERIAL REQUIRED TO IMPROVE A VISUAL APPEARANCE OF AN ULTRA-VIOLET RADIATION SOURCE

EP4740713A1EP 4740713 A1EP4740713 A1EP 4740713A1EP-4740713-A1

Abstract

Ultra-violet radiation source (2), in particular an LED emitter or LED device, comprising at least one LED-element (4) with a principle band gap radiation at a wavelength smaller or equal than 380nm and a preferably translucent substrate (6), on which the at least one LED-element (4) is arranged; wherein the at least on LED-element (4) and the translucent substrate (6) are encapsulated in a translucent material (12); characterized in that an predetermined amount of a fluorescent material (14) to cause a fluorescent-material-radiation in a visible wavelength range from 380-780nm, preferably from 400-500nm, is at least partially dispersed in the translucent material (12) and/or onto the at least one LED-element (4) and/or onto or into the translucent substrate to convert a part of the total radiant power of the at least one LED-element (4) into visible light; and wherein the converted part is between 0.1% and 10% of the total radiant power of the at least one LED-element (4).

Inventors

  • HOOKER, JAMES
  • BROEDERS, FRANK
  • GEENS, RUDY
  • VINCKX, Wim
  • GIELEN, Jos
  • LOYSCH, Nicole

Assignees

  • Flowil International Lighting (Holding) B.V.

Dates

Publication Date
20260513
Application Date
20230707

Claims (11)

  1. 1. Ultra-violet radiation source (2), in particular an LED emitter or LED device, comprising: - at least one LED-element (4) with a principle band gap radiation at a wavelength smaller or equal than 380nm and - a preferably translucent substrate (6), on which the at least one LED- element (4) is arranged; wherein the at least on LED-element (4) and the translucent substrate (6) are encapsulated in a translucent material (12); characterized in that an predetermined amount of a fluorescent material (14) to cause a fluorescent-material-radiation in a visible wavelength range from 380- 780nm, preferably from 400-500nm, is at least partially dispersed in the translucent material (12) and/or onto the at least one LED-element (4) and/or onto or into the translucent substrate to convert a part of the total radiant power of the at least one LED-element (4) into visible light; and wherein the converted part is between 0.1% and 10% of the total radiant power of the at least one LED-element (4).
  2. 2. Ultra-violet radiation source (2) according to claim 1, wherein the fluorescent material (14) comprises a peak radiation wavelength in the blue wavelengths, namely between 400-500nm.
  3. 3. Ultra-violet radiation source (2) according to claim 1 or 2, wherein the converted part of the radiation is with regard to the radiant power predominantly in the blue range between 400nm and 500nm, that is that more than 70%, preferably more than 80% of the radiant power of the radiation in the visible range between 380nm and 780nm is in the blue range that is between 400nm and 500nm.
  4. 4. Ultra-violet radiation source according to any of the preceding claims, wherein the predetermined amount of the fluorescent material (14) comprises a dose weight between O.lmg and 2.5mg.
  5. 5. Ultra-violet radiation source (2) according to any of the preceding claims, wherein the unconverted part of the total radiant power of the at least one LED-element (4) is at least 70%, preferably at least 90%, more preferably between 99.9% and 90%.
  6. 6. Ultra-violet radiation source (2) according to any of the preceding claims, wherein the fluorescent material (14) comprises or is phosphor, preferably Europium-activated Strontium Chlorophosphate (Sr 3 (PO4) 3 CI:EU 2+ ).
  7. 7. Ultra-violet radiation source (2) according to any of the preceding claims, wherein a grain diameter of the fluorescent material (12) is smaller than 10pm.
  8. 8. Method for determination of a necessary dose of a fluorescent material (14) required to improve a visual appearance of an ultra-violet radiation source (2), wherein the ultra-violet radiation source (2) comprises at least one LED-element (4) encapsulated by a translucent material (12); the method comprising the following steps: - determining an absolute parasitic luminescence spectrum for the ultraviolet radiation source (2); - obtaining a pure and uncontaminated band gap radiation; - determining a radiation produced by the fluorescent material (14); - identifying the necessary dose of the fluorescent material (14) depending on the determined radiation of the fluorescent material (14) and on a diameter of the translucent material (12).
  9. 9. Method according to claim 7, wherein the absolute parasitic luminescence spectrum is determined by multiplying a spectral power distribution form the parasitic luminescence by its peak radiant flux at a wavelength of 550nm.
  10. 10. Method according to claim 7 or 8, wherein the pure and uncontaminated band gap is obtained by substraction of the parasitic luminescence spectrum from a measured spectrum of the ultra-violet radiation source (2).
  11. 11. Method according to any of claims 7 to 9, wherein the radiation produced by the fluorescent material (14) is determined by the comparison of a plurality of LED-elements (4), wherein the only variable is a dose weight of the fluorescent material (14).

Description

Ultra-violet radiation source and method for identification of a necessary dose of a fluorescent material required to improve a visual appearance of an ultra-violet radiation source Description The present invention relates to an ultra-violet radiation source according to the subject-matter of claim 1. The present invention specifically relates to an ultra-violet radiation source, in particular an LED-emitter or an LED-device and a method for identification of a necessary dose of a fluorescent material required to improve a visual appearance of an ultra-violet radiation source. The present invention is applicable to conventional linear LED light sources in which multiple LEDs are used in the LED units, as well as to linear LED filament light sources. Prior art ultraviolet LEDs having their peak emission at wavelengths below 380nm are plagued by variations in the colour of emitted light between individual LEDs, as well as from batch-to-batch. This results in an unsightly appearance. The root cause of this problem is that LEDs typically radiate two or more distinct spectra. The vast majority of their radiation is at a particular wavelength range that is determined by the electronic band gap of the semiconductor material - this is known as the band gap radiation. However, all semiconductor devices, including LED chips, contain traces of impurities as well as lattice defects in the crystalline matrix. Both can lead to the generation of parasitic luminescence at wavelengths other than the intended band gap radiation. For the popular Indium or Aluminium Gallium Nitride (AIGaN or InGaN) based LEDs which are generally manufactured to produce a relatively narrow band gap radiation in the ultraviolet to green wavelength range of approx. 250-550nm, in all measured samples we also see a broad but rather weak parasitic luminescence in the green-yellow-red wavelength ranges from approximately 480-700nm. This band is typical for GaN-based LEDs and is due to deep level radiative transitions caused by Gallium vacancies. In case the principal band gap radiation is in the visible wavelength range, then the parasitic luminescence is greatly overpowered by the former and is of no consequence. However, in case the principal band gap radiation is in the ultraviolet wavelength range, which is invisible to the human eye, then the only detectable visible radiation is the parasitic luminescence caused by the impurities and lattice defects. Moreover, since this parasitic luminescence is caused by very tiny defects that are difficult to control, its magnitude can be highly variable both between individual LEDs from the same batch, as well as between different production batches. Additionally, there may be undesirable fluorescence effects of other LED components, such as sapphire substrates, which can themselves fluoresce when stimulated by wavelengths below 380nm. It is challenging to produce LED chips having sufficiently consistent impurity and/or defect levels to eliminate this variation in visible light emission. Consequently, prior art UV LEDs often have a white, yellow or green colour light. This is not always accepted by consumers of UV products, who are used to the typically violet-blue appearance of conventional traditional UV sources, and there is considerable market interest for UV-A LEDs that also have a similar blue appearance. Another drawback of prior art UV LEDs is that some appear to be much brighter than others - and sometimes if the impurity content is very low, the visible light output might also be very low. This is often misinterpreted by the end users as meaning that there are also variations in the UV output even though that is typically quite consistent - but of course not visible to the human eye. This leads to a fear of the customers that the LEDs having lower visible output are inferior or maybe also delivering so little LIV as to be useless. The present invention solves both these technical problems by a novel method To improve the LED chip manufacturing process and raw materials such that the concentration of impurities and defects is consistently held as low as possible, thereby minimising the magnitude and variation of parasitic luminescence at undesirable wavelengths. However, improving the LED chip manufacturing process typically requires raw materials having elevated chemical purity, and/or manufacturing equipment that is able to operate within narrower process tolerances. The result is increased product cost - however the process is also very challenging and another result is that many suppliers seem unable to translate these improvements, which can be achieved in the lab, into their manufacturing processes. Moreover, it is apparent that gradual improvements are achieved over time, which results in a continual decrease of the parasitic luminescence. As such it is not possible to combine LEDs made at one period of time with those made at a later date. This presents challenges in the field if produc