Flicker Reduction of AC LEDs by Mn<sup>2+</sup>Doped Apatite Phosphor

Korte, Simon; Lindfeld, Elisa; Jüstel, Thomas

doi:10.1149/2.0141803jss

Cited by 8 publications

(7 citation statements)

References 17 publications

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“…Flickering can be reduced by using phosphors which decay slowly, such as many Mn-based phosphors, which have typical decay times of several milliseconds. − This slow decay bridges the dark periods in which the LED is switched off, thereby reducing the flickering. But long decay times are often accompanied by saturation effects .…”

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confidence: 99%

Importance of Evaluating the Intensity Dependency of the Quantum Efficiency: Impact on LEDs and Persistent Phosphors

2018

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The quantum efficiency is a key metric in lighting technology and for the quantification of luminescent processes, indicating how many photons are emitted with respect to the number of absorbed photons. Ideally, this value should approach unity to reduce losses, for instance in the common phosphor converted white LEDs. In this work we demonstrate that in luminescent materials where energy can be stored at defect centers, like in the extreme case of persistent phosphors, the quantum efficiency depends on the excitation intensity. For the green emitting SrAl 2 O 4 :Eu 2+ ,Dy 3+ , which has been proposed for use in AC-LEDs, the internal quantum efficiency drops for increasing excitation intensity from 71% to 54%. At elevated excitation intensities, as encountered in LEDs, the trapped charge carriers can be optically detrapped by the excitation light, leading to this strong reduction of the overall quantum efficiency. Considering that the absorption cross section for this process is 6−29× larger than the absorption cross section for the luminescent ion, the efficiency of LED phosphors can be increased by avoiding the presence of defects acting as trapping centers. Finally, designing persistent phosphors with defects that show a limited optical response for the excitation light could strongly increase their energy storage capacity.

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confidence: 99%

Importance of Evaluating the Intensity Dependency of the Quantum Efficiency: Impact on LEDs and Persistent Phosphors

2018

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“…Despite so many potential advantages, a pressing issue limiting the commercial application of AC-LEDs is the flicker effect, which is mainly caused by the unavoidable 5–20 ms dimming time in each AC cycle. This effect may also induce headaches, eyestrain, and other symptoms in certain people 11 , 12 . Consequently, reducing the flicker effect has become the key issue for the further applications of AC-LED lighting systems.…”

Section: Introductionmentioning

confidence: 99%

Enhanced blue-light excited cyan-emitting persistent luminescence of BaLu2Al2Ga2SiO12:Ce3+, Bi3+ phosphors for AC-LEDs via defect modulation

et al. 2022

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Alternating current light-emitting diodes (AC-LEDs) have received significant attention from both academia and industry due to their remarkable benefits of more compact volume, cheaper manufacturing cost, greater energy usage efficiency, and longer service life. One of the most significant challenges for AC-LEDs is the flicker effect, which is mainly caused by the unavoidable 5–20 ms dimming time. Aiming to reduce the flicker effect, we designed a series of excellent blue-light excited cyan-emitting persistent luminescence (PersL) phosphors BaLu2Al2Ga2SiO12:Ce3+, Bi3+ via defect engineering of co-doping Bi3+. Interestingly, we found that co-doping Bi3+ not only effectively enhanced the PersL intensity, but also regulated the PersL lifetime of this phosphors. As the Bi3+ co-doping concentration increases to 0.01, the τ80 value (the time when the PersL intensity decreases to 80% of the initial intensity) increases from 0.24 to 19.61 ms, which proves to be effective in compensating the flicker effect of AC-LEDs. A new method of generating white light emission during the dimming time through adding the blue-light excited cyan PersL phosphor to the original orange-red PersL phosphor was proposed and an AC-LED lamp with a decreased percent flicker of 48.15% was fabricated, which is significantly better than the other currently reported AC-LED devices based on PersL phosphors. These results demonstrate that BaLu2Al2Ga2SiO12:Ce3+, Bi3+ might be an attractive material for low-flicker AC-LEDs.

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“…The decay time is a crucial factor. LPPs in AC‐LEDs with too low decay time reduce flickering, but with a too long decay time causes saturation and changes the emission color . This means that developing a single composition warm white‐emitting phosphors with a proper decay time helps obtain stable, comfortable, and healthy illumination sources.…”

Section: Introductionmentioning

confidence: 99%

Warm white light emitting from single composition SrGa₁₂O₁₉:Dy³⁺ phosphors for AC‐LED

et al. 2019

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Making illumination light sources become comfortable to the human eye is a long‐term effort, which justifies the current research on warm white‐light‐emitting diodes (w‐LEDs). In this work, a novel phosphor for w‐LEDs, namely SrGa12O19: Dy3+(SGO: Dy3+), with a low‐color temperature (CT) was designed and synthesized. The crystal structure, the luminescence properties, the thermoluminescence properties and the stability of SGO: Dy3+ were investigated. We demonstrate outstanding luminescent characteristics and excellent stabilities. The intensity of emission light keep remained when excited by a flickering light source with a chopping speed or off‐time of a few seconds, which indicates that the SGO: Dy3+ phosphor has anti‐flicker properties that will be useful for potential applications, as LEDs driven by alternating current (AC‐LED). The chromaticity coordinates and the correlated color temperature (CCT) of SGO: Dy3+ phosphors with different Dy3+ concentrations are close with an optimal doping at 4.00 mol% Dy3+ for chromaticity coordinate (0.4269, 0.4348) and a lowest CCT of 3361 K. The perfect weatherability of this phosphor was also confirmed since the phosphorescence intensity and the color were stable at high temperature and in a high humidity environment. The performance obtained shows that SGO: Dy3+ is a suitable candidate for illumination sources that are beneficial to human health.

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Flicker Reduction of AC LEDs by Mn²⁺Doped Apatite Phosphor

Cited by 8 publications

References 17 publications

Importance of Evaluating the Intensity Dependency of the Quantum Efficiency: Impact on LEDs and Persistent Phosphors

Importance of Evaluating the Intensity Dependency of the Quantum Efficiency: Impact on LEDs and Persistent Phosphors

Enhanced blue-light excited cyan-emitting persistent luminescence of BaLu2Al2Ga2SiO12:Ce3+, Bi3+ phosphors for AC-LEDs via defect modulation

Warm white light emitting from single composition SrGa₁₂O₁₉:Dy³⁺ phosphors for AC‐LED

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Flicker Reduction of AC LEDs by Mn2+Doped Apatite Phosphor

Cited by 8 publications

References 17 publications

Importance of Evaluating the Intensity Dependency of the Quantum Efficiency: Impact on LEDs and Persistent Phosphors

Importance of Evaluating the Intensity Dependency of the Quantum Efficiency: Impact on LEDs and Persistent Phosphors

Enhanced blue-light excited cyan-emitting persistent luminescence of BaLu2Al2Ga2SiO12:Ce3+, Bi3+ phosphors for AC-LEDs via defect modulation

Warm white light emitting from single composition SrGa12O19:Dy3+ phosphors for AC‐LED

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Flicker Reduction of AC LEDs by Mn²⁺Doped Apatite Phosphor

Warm white light emitting from single composition SrGa₁₂O₁₉:Dy³⁺ phosphors for AC‐LED