Utilizing SrSi 2 O 2 N 2 :Eu 2+ ,Yb 2+ phosphor to achieve high hue rendering index and high hue stability

ABSTRACT


INTRODUCTION
Nowadays, InGaN-based diodes emit white-light emitting diode (WLED) are gaining popularity in the future illumination stage owing to the numerous benefits when they are utilized in incandescent bulbs, including high performance, an ecologically friendly character, dependability, small size, longevity, and so on [1], [2].The most typical method to generate white illumination is to mix an InGaN blue LED chip with a Y3Al5O12:Ce 3+ (YAG) yellow phosphor [3].Nevertheless, the use of them is restricted since the emitted illumination cannot achieve a good color balance for accurate color representation without the presence of red illumination.To address this issue, several phosphor-based LEDs were used to boost red luminescence [4].The multiple-phosphor technique outperforms the YAG:Ce 3+ blue LED chip technique in terms of color rendering (Ra), effectiveness, and luminosity.Nonetheless, the varying heat quenching of the separate phosphors produces color rendering aberration versus supplied power, as well as an improvement in productivity expense for actual usage.The varied phases of phosphors, on the other side, cause a decrease in Bulletin of Electr Eng & Inf ISSN: 2302-9285  Utilizing Utilizing SrSi2O2N2:Eu 2+ ,Yb 2+ phosphor to achieve high hue rendering index … (Ha Thanh Tung)

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illuminating effectiveness according to the re-absorptivity within multi-phosphor-based LEDs [5], [6].The use of a filled-hue producing one-phase phosphor built by oxide and silicate compositions led to a highly steady color rendering against a supplied power [7]- [9].Lately, nitridosilicate and oxynitridosilicate-based down-transformation phosphors have demonstrated excellent temperature stability and good illuminating performance [10], [11].Hedili et al. [10] noted the illuminating characteristics and configuration of a Eu 2+ and Yb 2+ doped SrSi2O2N2 (SSON) oxynitridosilicate phosphor with wide-range emission in the green to orange area, a full width at half maximum (FWHM) (entire breadth at half-maximal) of 170 nm, and exterior quantum productivity of about 16% with 450 nm stimulation [12]- [14].The transferring power from Eu 2+ and Yb 2+ ions was validated by the writers.The configuration among luminescence characteristics of a two-hue producing SSON:xEu 2+ , yYb 2+ oxynitridosilicate are described in this study.The resulting phosphor was employed as a solitary illumination converter link to a blue-releasing LED chip to provide heated illumination which has a great hue rendering indicator and steady Commission Internationale de L'Eclairage, International Commission on Illumination (CIE) over a broad forward-bias current range.

EXPERIMENTAL
SSON:Eu,Yb green to orange illuminating phosphor was synthesized using Si3N4, SrCO3, Eu2O3, and Yb2O3.All components with a purity of at least 3N were utilized with no additional cleanse.The stoichiometric number of the initial components was carefully combined with ethanol and mixed in an agate mortar before going through 2-hour drying in an oven at 120 °C.We packed the powder mixes in an alumina crucible and heated them in a horizontal alumina tube furnace with a N2/H2 (5%) gas flow, at 1400 °C, lasting 8 hours.The doses of Eu 2+ ion stayed at 2 at% in comparison to Sr 2+ ion, whereas the Yb 2+ ion quantity was changed 0% to 8%.After burning, a gently sintered specimen was acquired, which was subsequently preliminary turned into fine powders by grinding.These fine powders were then used to produce white-light LED.The resulting SSON:Eu,Yb powder was integrated with silicon resin.After that, we packed them above an InGaN-based blue chip and left them dry at 120 °C for 2 hours [15], [16].
Analyses of phase composition were performed using an X-ray diffractometer; with Cu Kα (λ=1.542Å) at normal temperature.We also examined the microstructure of the produced powder using the scanning electron microscope.At normal temperature, the luminescence spectra were achieved utilizing a fluorescence spectrophotometer with a 150 W Xe light as a stimulation supply.The decomposition period was measured using the streak camera C4334.The integrated sphere approach was used to calculate quantum effectiveness.PTE-VUVD2L-100 was used to evaluate heat quenching.

RESULTS AND DISCUSSION
As maximum points of all specimens' X-ray diffraction patterns are reasonably close to the SSON reference.In comparison to the findings provided by Chen et al. [15], the produced outcome includes almost entirely a solitary stage.It also has no substantial amounts of impurities like Sr2SiO4.When there is the addition of Yb 2+ , a high point at 28°, this may be seen in numerous specimens, although its origin is unknown.Eu 2+ (1.17 Å, 6-coordination number) and Yb 2+ (1.14 Å, octahedral coordination) have ionic radii that are similar to Sr 2+ (1.18 Å, 6-CN.)As previously demonstrated, Eu 2+ -Yb 2+ cations preferentially inhabit the Sr 2+ -points within the SSON lattice.The solid-solution phase formation when SSON is doped with Eu 2+ -Yb 2+ is suggested by the minor displacement of the position of the X-Ray diffraction analysis (XRD) peaks in our studies [17]- [19].
The SSON:Eu 2+ phosphor emitting spectra reveal a solitary emitting range reached a peak at 540 nm, which is ascribed toward the Eu 2+ ion's 4f 6 5d 1 → 4f 7 5d 0 transfer.Based on the increased degree of covalency among the activator ion and surrounded ligands, the radiation is noticed at longer wavelengths when tried to compare to common silicate/aluminate-based phosphors.The emitting band has a FWHM of 76 nm.The stimulation bands of color of Eu 2+ at 540 nm indicate a stimulation range within the region 200 to 500 nm.The stimulation spectra contain multiple unresolved sub-bands attributable to Eu 2+ ion stimulated states 4f 6 5d 1 .The radiation of Yb 2+ doped SSON phosphor is a solitary radiation range that peaks at 612 nm and is ascribed to relaxation to the 4f 13 5d 0 stage of Yb 2+ ions (FWHM=130 nm).The stimulation SSON:Yb 2+ phosphors' bands of color are composed of many ranges, one of which is attributed to the f−d transfer.The light was attributed to Yb 2+ -trapped exciton luminescence.Notably, the stimulation spectra of SSON:Yb 2+ are overlapped by part with the emitting spectrum of SSON:Eu 2+ phosphor within the 470 to 550 nm region.The power transferring ratio is proportional to the spectral overlapping among the emitting range of the power donor (Eu 2+ ) and the absorption range of the power acceptor (Yb 2+ ).
The light decomposition curves could be greatly represented by dual-exponential decomposition curve in (1) [20]: Here,  is the luminous strength;  denotes the duration;  1 and  2 are constant factors;  1 and  2 denote the short and long lifespan for exponential elements, in turn.The mean decay period ( * ) can be computed using (2) according to the specified numbers for all of the parameters as stated before [21]: Once the converting phosphor is in near closeness to the LED chip, its heating behavior is critical.Because of the little chip surface and restricted phosphor region, heating control is a significant consideration in LED configuration.Heats of 400 to 450 K can be attained close to the LED chip, though.Consequently, even at these high temperatures, the phosphor must retain quantum effectiveness and spectrum properties.The former is determined by the total emission strength being thermally quenched.In the latter case, changing and/or expanding the emission spectrum can change the overall emitting color of the device.Furthermore, the stimulation spectrum can shift, impacting the imbibed tiny part of the pumping LED's output.As a result, a phosphor assessment needs to include a minimum of research on heat extinguishing behavior, which means the change of emitting strength (preferably the quantum effectiveness).The decay period of luminescence in first order has comparable temperature behavior to that of strength quenching.
Figure 1 illustrates the opposite shift between the SSON:Eu,Yb and YAG:Ce 3+ weight percentages for retaining mean correlated color temperatures (CCTs).Additionally, this inverse proportion contributes to influencing the dispersion and absorbance of light beams in WLED's double-film configuration, which greatly impacts the WLEDs' color standard and illuminating effectiveness.Thus, the SSON:Eu,Yb concentration chosen specifies the WLEDs hue standard.Once the SSON:Eu,Yb proportion raised 2% to 20% wt., the YAG:Ce 3+ dosage declined to retain the median CCTs.WLEDs with hue temperatures among 5600 K and 8500 K also exhibit this characteristic.
Figure 2 shows SSON:Eu,Yb green phosphorus concentration has an influence on the WLEDs' transmission spectrum at 3000 K CCT.It is feasible to choose depending on the requirements provided by the producer [22].WLEDs that need high hue quality might somewhat reduce illumination.Figure 2 shows white illumination is the combination of the spectral area.As can be seen, the strength trend rises with SSON:Eu,Yb content in 420 to 480 nm and 500 to 640 nm emission wavelengths.The shift in the two-range emitting bands of hue indicates the growth in illumination generating intensity.Furthermore, the enhancement in blue-illumination dispersion in WLEDs implies that the dispersion of light within the phosphor package of the WLED is improved and helps to achieve better chromatic consistency and fidelity.It is well-known that managing to achieve better color uniformity with CCT greater than 5000 K is challenging for remote-phosphor configuration.These results, however, proved that SSON:Eu,Yb could help the producers to reach their goal of regulating color quality at poor and elevated CCTs (5600 K and 8500 K). improving WLED luminous strength.Next, the color divergence was investigated and demonstrated in Figure 4.The figure showed that the variation in chromaticity notably declined with the phosphor SSON:Eu,Yb proportion in all median CCTs.This can be explained by the absorbance feature of the SSON:Eu,Yb green phosphor.When the SSON:Eu,Yb phosphor collects the LED-chip blue illumination, it generates green radiation from converting the absorbed blue one.SSON:Eu,Yb also collect YAG:Ce-emitted yellow rays but owing to the absorbing qualities of the material, the blue-illumination absorption is greater.Hence, the addition of SSON:Eu,Yb encourages the green-emission parts in WLEDs to grow, leading to a more homogeneous chromaticity.Uniformity of chromaticity is a crucial feature among the latest parameters of the modern WLED lamp.Thus, possessing a high color-uniformity specification could contribute to increasing the price of a WLED lamp in the marketplace.The advantage of employing SSON:Eu,Yb is its inexpensive cost.SSON:Eu,Yb can thus be commonly employed.
Hue homogeneity is only one factor to look at in the assessment of WLEDs' chromaticity performance.Hue quality cannot be claimed to be good when it only has a good indicator of color uniformity.Thus, another parameter was developed to combine the color uniformity with other evaluation factors This indicator is color quality scale (CQS), which can access the color rendition indicator (CRI) and color uniformity while considering the visual inclination of observers [23]- [25].The data recorded on CQS is shown in Figure 5, in which the growth in CQS in the existence of the distant phosphor film SSON:Eu,Yb is observed.Additionally, the CQS does not significantly change with SSON:Eu,Yb concentrations lower than 10% wt., when the SSON:Eu,Yb concentration is increased.Besides, this study demonstrates the CRI results to observe the influence of SSON:Eu,Yb on each color indicator.The CRI results depicted in Figure 6 show that the phosphor SSON:Eu,Yb is not advantageous for this indicator.CRI shows a small reduction when there is the distant phosphor SSON:Eu,Yb sheet.Additionally, when the SSON:Eu,Yb concentration exceeds 10% wt., CQS and CRI decrease remarkably based on severe hue loss when green emission is so intense that breaks the color balance of the chroma range (including blue, green, and yellow) [26], [27].Consequently, we should choose the suitable concentration of SSON:Eu,Yb to meet the specific lighting requirements.pattern merely slightly diminishes CRI.For CQS assessment, the root mean square aberration would be employed, negatively affecting huge disparities in a greater way.CRI carries a downside in that minimal value zero of   does not exist.In one instance, assessment results in one   value of -47 in the case of small pressure sodium lights.CQS can solve the downside by employing a normalization formula, giving various results in the range of 0 to 100 [26]: Human usually perceive items through clear and saturated hues instead of rays giving flat looks.Such a behavior resulted in creating elements to assess the attractiveness of items lit by testing ray.Compared to sun ray, particular rays can give items a better appearance, resulting in a CRI over 100.All hue disparities among the testing ray and the reference ray would result in an   falling 100, since the reference ray would be identical to a "sublime" ray.Judging CQS' nature, rays resulting in hue generation items having identical hue and greater saturation compared to the reference ray, receive no penalty, save for the "sublime" CQS value.For CRI, rays that exhibit huge (blue) as well as small (red) CCT may still give one huge   result, which applies to reference rays with identical CCTs.On the other hand, the hue generation capability for these rays would be small.The rays merely generate lesser hue scale uncanny to human eyes.CQS applies lesser rendering index to such rays, based on the hue scale zone for fifteen hue patterns.CQS holds many advantages to surpass CRI.On the other hand, this element is affected by the task of choosing reference rays or unlimited quantity for reference rays for our study, since the reference rays is determined by the testing ray's CCT.

CONCLUSION
Finally, for the first time, a two-hue releasing SSON:Eu,Yb oxynitridosilicate phosphor for solitary usage in a heated white LED has been produced.The SSON:Eu,Yb phosphor produced exhibits wide range emitting concentrated at 540 and 612 nm for the Eu 2+ and Yb 2+ ions, accordingly.The proportionate percentage of green and orange radiations was revealed for being dependent upon this activator ion concentration of the phosphor.The power transmission from Eu 2+ ion to Yb 2+ trapping sites was verified by the rapid decay period of Eu 2+ radiation.The white LED, which combines a 450 nm producing InGaN chip with a dual-hue producing SSON:Eu,Yb phosphor, emits heated white illumination with a great hue rendering indicator and outstanding hue steadiness versus energy supply.

Figure 1 .Figure 2 .
Figure 1.Adjusting the dosage of phosphor to maintain the median CCT