RU2536767C2 - Method of obtaining modified trichromatic led sources of white light - Google Patents

Abstract

FIELD: physics, optics.

SUBSTANCE: invention relates to field of lighting engineering and, in particular, to LED sources of white light based on dark blue (450-455 nm), green (525-535 nm) and red (605-615 nm) light-emitting diodes, named after RGB integration as a triad. The method of obtaining of modified trichromatic sources of white light by means of application on RGB triad of light-emitting diodes of suspension of dark blue light-induced luminophor, meanwhile the luminophor functions are performed by the activated cerium with the composition Ln_3+αAl₅O_12+1.5α of off-stoichiometric composition, where Ln - yttrium or together with it one or several rare earth elements containing excessive Ln in relation to Al so what the value of the coefficient α varies within the interval 0<α≤0.45, or cerium-activated composition Ln_3+αAl₅O_12+1.5α of off-stoichiometric composition, where Ln - yttrium or together with it one or several rare earth elements containing insufficient Ln in relation to A1 so what the value of the coefficient α varies within the interval 0<α≤1.5, or europium-activated silicate luminophors with the general formula (Sr-Ba-Ca)₂SiO₄ and (Sr-Ba-Ca)SiO₃, having yellow-green or yellow luminescence at excitation by dark blue light.

EFFECT: invention provides improvement of quality of colour transfer and increase of efficiency of light transformation by trichromatic LED sources of white light.

6 tbl, 5 ex

Description

The invention relates to the field of lighting engineering and, in particular, to LED white light sources based on LEDs of blue (450-455 nm), green (525-535 nm) and red (605-615 nm), called after combining the RGB triad. Light sources of this type are widely used in household and decorative lighting systems.

A significant drawback of industrial white light sources based on LEDs with narrow spectral (20-30 nm) lines is the low level of color rendering quality. This parameter is determined by the values of the general (Ra) and partial color rendering indices (R). In industrial three-color white light sources, the overall color rendering index (Ra) usually does not exceed 70 units (with a physiologically acceptable norm of 80-95 for indoor units). This is due to the low values of particular color rendering indices characterizing the contribution to the total luminous flux of saturated red radiation (R9), saturated yellow (R10), saturated green (R11) and saturated blue (R12).

The color rendering quality in RGB white light sources depends on the position of the maxima and the intensity of the light emitted by each LED. The light intensity, in turn, depends on the density of the current passing through the LED. An increase in it is always accompanied by an increase in the temperature of the pn junction, which in turn leads to a broadening of the emitted spectral line and a change in the position of the maximum on the spectral curve. Moreover, each of these values for different lines has its own temperature coefficient. Therefore, the search for color balance in sources of this type achieved by correcting the radiation power of all radiation components for a given color temperature of a white light source or a given radiation spectrum is a rather difficult task, which is also a disadvantage of devices of this type.

The third disadvantage is the low volume uniformity of color. The color of the white light source should not depend on the direction of the radiation. In industrial RGB sources, the distance between the LEDs in the triad can exceed 1 mm, and under these conditions, the source of each light becomes physically distinguishable, which leads to a decrease in the efficiency of the system as a whole.

In the article [Zukauskas A., a.o. nd "Optimization of white polychromatic semiconductor lamps": Appl. Phys. Lett. 80, 234 (2002b)] describes various methods for optimizing the optical parameters of multi-color LED white light sources based on physical control principles. In relation to industrial white light sources intended for domestic and decorative lighting, these techniques are quite complex and involve the need for periodic adjustment of electrical parameters.

The present invention seeks to address these disadvantages of traditional RGB white light sources.

The technical result of the invention is to improve the color rendering quality and increase the light conversion efficiency of tri-color LED white light sources. This result is achieved by the method of obtaining modified tri-color LED white light sources, namely, that a suspension of a phosphor excited by blue light is applied to the RGB triad in a curable optically transparent photo- and heat-resistant polymer.

As a phosphor can be used:

1) cerium-activated phosphors of the stoichiometric garnet family Ln ₃ Al ₅ O ₁₂ , where Ln is yttrium or, together with it, one or more rare-earth elements;

2) cerium-activated compositions Ln _{3 + α} Al ₅ O _{12 + 1.5α of} non-stoichiometric composition, where Ln is yttrium or with it one or more rare-earth elements containing an excess of Ln with respect to Al, so that the value of the index α varies in the range 0 <α≤0.45, and in which case, in contrast to the stoichiometric garnet, the ratio between Ln: Al: O is not equal to 3: 5: 12 and is (3 ÷ 3.45): 5: (12 ÷ 12.67);

3) cerium-activated compositions of Ln _3-α Al ₅ O _{12-1.5α of} non-stoichiometric composition, where Ln is yttrium or with it one or more rare-earth elements containing a deficiency of Ln with respect to Al, so that the value of the index α varies in the range 0 <α≤1.5, and in which case, in contrast to the stoichiometric garnet, the ratio between Ln: Al: O is not equal to 3: 5: 12 and is (3 ÷ 1.5): 5: (12 ÷ 9.75) ;

4) europium activated silicate phosphors of the general formula (Sr-Ba-Ca) ₂ SiO ₄ and (Sr-Ba-Ca) SiO ₃ having yellow-green or yellow luminescence upon excitation by blue light. The observed effect of increasing the color rendering quality and light conversion efficiency is due to the improvement of the volumetric color uniformity achieved as a result of scattering of each of the color components in the applied dispersion medium and a significant broadening of each of the color bands.

Practical examples

The following examples No. 1-5 show how the lighting characteristics of a three-color LED white light source change when it is modified by applying a suspension of phosphors of various compositions to the RGB triad. Table 1 (see the graphic part) shows the optical characteristics of these phosphors (color coordinates - x and y, the position of the maximum in the luminescence spectrum - λ _p (nm), the dominant wavelength in the luminescence spectrum - λ _d (nm), color temperature - T _c (K), spectral width at half-height - Δλ (nm), luminescence brightness when excited by light with a wavelength of 460 nm (% in relation to the Nemoto "902" standard).

Example No. 1

A suspension of powdered phosphor FL 4255 was deposited on a protective lens of a commercially available tri-color LED white light source, the spectrum and optical parameters of which are shown on the left side of Table 2 (see the graphic part). This phosphor was a non-stoichiometric composition containing an excess of yttrium and rare earths with respect to aluminum in comparison with this ratio in a stoichiometric garnet of 3: 5.

A suspension containing 0.5 g of phosphor was prepared in a solution of silicone (2 ml) and hardener (2 ml). 2 drops of the prepared suspension were applied using an industrial dispenser onto the surface of the triad's RGB protective lens. Data on the optical parameters of the modified light source are given in the right part of Table 2.

As you can see, the modification of the RGB source leads to a fundamental change in all optical characteristics, an increase in the total and the entire set of private indices, as well as an increase of more than 50% in the total luminous flux, the value of which is proportional to the efficiency of the light source. It should also be noted a significant expansion of all base bands and an increase in the intensities of the bands of green and red light.

The color temperature of the modified source was close to the standard of normal white.

Example No. 2

In this case, in contrast to example No. 1, the applied phosphor in composition corresponded to a stoichiometric garnet. It was characterized by a slightly lower color temperature. The experimental technique did not differ from that described in example No. 1.

It can be noted that in this case, there is a more significant increase in the general and particular color rendering indices, as well as a decrease in the color temperature to the standard of normal white color, both in terms of the color temperature and the entire set of color rendering indices.

The increase in the total luminous flux is maintained at the level of example No. 1.

Example No. 3

In this example, the applied phosphor was a composition of non-stoichiometric composition containing a lack of yttrium and rare earth elements with respect to aluminum in comparison with a ratio in the stoichiometric garnet of 3: 5. The gadolinium content in the sample was significantly higher than in the phosphor used in example No. 1. The data given in Table 4 (see the graphic part) show that the tendency observed in the previous cases is reproduced, namely: there is a further improvement in all the lighting parameters of the modified white light sources, approaching a possible maximum of values with respect to the selected initial a three-color LED white light source (Table 4).

Examples No. 4 and No. 5.

In these examples, cerium-activated non-stoichiometric compositions with an excess of aluminum with respect to Ln were used, characterized by a high content of gadolinium. As a result, the phosphors had a yellow-orange glow. It is known that, in contrast to yellow-green and yellow phosphors, they have lower brightness and are characterized by lower color temperatures. Therefore, the use of such phosphors for modifying tricolor sources does not lead to a fundamental change in the achieved high level of color rendering indices, but is accompanied by a decrease in the relative fraction of blue radiation and a decrease in the total luminous flux. At the same time, the color temperature drops to values characteristic of warm white light (see tables 5 and 6 in the graphic part).

It should be noted that even in the most unfavorable case (example No. 5), the efficiency of the modified RGB white light source is more than 30% higher than the level characterizing industrial designs.

Thus, the use of yellow-green, yellow and yellow-orange phosphors excited by blue and, partially, green light allows after applying them to the surface of industrial three-color LED white light sources to significantly improve the whole range of their lighting parameters, namely:

- increase the overall color rendering index to values> 84 and private color rendering indices R9-R14> 75-85;

- increase, ceteris paribus, the total luminous flux by 30-50%;

- reduce the color temperature to values that correspond to warm white light.

Claims (1)

A method for producing modified three-color white light sources by applying a suspension of a blue-excited phosphor to the RGB triad of LEDs, characterized in that cerium-activated non-stoichiometric compositions Ln _{3 + α} Al ₅ O _{12 + 1,5α} are used as the phosphor, where Ln is yttrium or together with it one or more rare earth elements containing an excess of Ln with respect to A1 so that the value of the index α varies in the range 0 <α≤0.45,
or cerium-activated compositions of Ln _{3 + α} Al ₅ O _{12 + 1,5α of} non-stoichiometric composition, where Ln is yttrium or with it one or more rare-earth elements containing a deficiency of Ln with respect to A1 so that the value of the index α varies in the range 0 <α≤1.5,
or europium activated silicate phosphors of the general formula (Sr-Ba-Ca) ₂ SiO ₄ and (Sr-Ba-Ca) SiO ₃ having yellow-green or yellow luminescence upon excitation by blue light.

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