Optical Materials

2015

DOI: 10.1016/j.optmat.2015.05.020

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Abnormal blue-shift of Eu2+-activated calcium zirconium phosphates CaZr4(PO4)6

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Cited by 9 publications

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“…The red light emission of Sr 2 Si 5 N 8 :Eu 2+ phosphor is generated by electron transition of Eu 2+ ion from 4f 6 5d 1 excited state to 4f 7 ground state (Jia and Wang, 2007). There are two cations sites (Sr 1 and Sr 2 ) in Sr 2 Si 5 N 8 crystal lattice (Zhang and Yang, 2015). Sr 1 site is ten-coordinated with N atoms where its Sr 1 -N bond has a mean distance of 2.865 Å (Zhang and Yang, 2015; Baginskiy et al , 2011).…”

Section: Resultsmentioning

confidence: 99%

“…There are two cations sites (Sr 1 and Sr 2 ) in Sr 2 Si 5 N 8 crystal lattice (Zhang and Yang, 2015). Sr 1 site is ten-coordinated with N atoms where its Sr 1 -N bond has a mean distance of 2.865 Å (Zhang and Yang, 2015; Baginskiy et al , 2011). Meanwhile, Sr 2 site is eight-coordinated to N atoms where its Sr 1 -N bond has a mean distance of 2.928 Å (Zhang and Yang, 2015; Baginskiy et al , 2011).…”

Section: Resultsmentioning

confidence: 99%

“…Sr 1 site is ten-coordinated with N atoms where its Sr 1 -N bond has a mean distance of 2.865 Å (Zhang and Yang, 2015; Baginskiy et al , 2011). Meanwhile, Sr 2 site is eight-coordinated to N atoms where its Sr 1 -N bond has a mean distance of 2.928 Å (Zhang and Yang, 2015; Baginskiy et al , 2011). Sr 1 -N bond, which has shorter bond length and tighter crystal circumstance of Eu 2+ ion, contributes to shorter wavelength and higher energy photon emission [Eu(I)] (Zhang and Yang, 2015; Baginskiy et al , 2011).…”

Section: Resultsmentioning

confidence: 99%

“…Meanwhile, Sr 2 site is eight-coordinated to N atoms where its Sr 1 -N bond has a mean distance of 2.928 Å (Zhang and Yang, 2015; Baginskiy et al , 2011). Sr 1 -N bond, which has shorter bond length and tighter crystal circumstance of Eu 2+ ion, contributes to shorter wavelength and higher energy photon emission [Eu(I)] (Zhang and Yang, 2015; Baginskiy et al , 2011). Meanwhile, Sr 2 -N bond, which has longer bond length and looser crystal circumstance of Eu 2+ ion, contributes to longer wavelength and lower energy photon emission [Eu(II)] (Zhang and Yang, 2015; Baginskiy et al , 2011).…”

Section: Resultsmentioning

confidence: 99%

“…Sr 1 -N bond, which has shorter bond length and tighter crystal circumstance of Eu 2+ ion, contributes to shorter wavelength and higher energy photon emission [Eu(I)] (Zhang and Yang, 2015; Baginskiy et al , 2011). Meanwhile, Sr 2 -N bond, which has longer bond length and looser crystal circumstance of Eu 2+ ion, contributes to longer wavelength and lower energy photon emission [Eu(II)] (Zhang and Yang, 2015; Baginskiy et al , 2011). Figure 6(b) displays configurational coordinates of Eu 2+ ion at high temperature (Majekodunmi, 2015).…”

Section: Resultsmentioning

confidence: 99%

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Implementation of phosphor sedimentation to reduce thermal instability issue affecting white LED luminescence

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2019

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Purpose In general, lighting application, white light emitting diode (LED) usually exposed to an extreme operating temperature of above 90°C. It is well-known that luminous efficacy and spectral characteristic of white LED are dependent on the temperature, causing thermal effects on luminous efficacy and color shift of white LED become a critical application checkpoint to be addressed by white LED manufactures. Thus, the purpose of this paper is to minimize the thermal stability issue affecting white LED luminescence during operation by introducing phosphor sedimentation process. Design/methodology/approach The LED samples were assembled and sent for centrifugation with 0, 5 and 10 revolutions per second (rps), respectively, during phosphor sedimentation process. Luminescence properties of these LED samples were then characterized at a varying temperature to investigate the effect of phosphor sedimentation on the luminescence stability of LED samples. The LED samples were also cross-sectioned and analyzed to understand the phosphor sedimentation mechanism. Computational fluid dynamics (CFD) was applied to study the temperature distribution of the non-phosphor sediment (NPS) and phosphor sediment (PS) LED during operation to validate the hypotheses based on experimental data. Findings Experimental results show that the luminous intensity of PS LED samples degrades less significant at high temperature. The experimental results also show that the color coordinate for PS LED samples is more stable and is less blue-shifted than NPS LED samples as the temperature increased. These are because the heat generated by phosphor particles during operation can be dissipated effectively throughout a high thermal conductivity substrate after phosphor sedimentation. Thus, the phosphor temperature of PS LED is lower than NPS LED during operation as validated with the thermal simulation. Practical implications The study of this paper is applicable as a reference for industries who intend to resolve the thermal stability of white LED during operation. The luminescence properties changes as a function of the temperature study in this paper can be used to predict the application performances of white LED accurately. Apart from that, the analysis method of temperature distribution using CFD simulations can be extended by other CFD users in the future. Originality/value Implementation of phosphor sedimentation to reduce thermal instability issue of white LED has yet to be reported on previous studies. Most literature just studied the thermal instability issue of either assembled LED or raw material, without suggesting any solution to tackle the issue.

“…The red light emission of Sr 2 Si 5 N 8 :Eu 2+ phosphor is generated by electron transition of Eu 2+ ion from 4f 6 5d 1 excited state to 4f 7 ground state (Jia and Wang, 2007). There are two cations sites (Sr 1 and Sr 2 ) in Sr 2 Si 5 N 8 crystal lattice (Zhang and Yang, 2015). Sr 1 site is ten-coordinated with N atoms where its Sr 1 -N bond has a mean distance of 2.865 Å (Zhang and Yang, 2015; Baginskiy et al , 2011).…”

Section: Resultsmentioning

confidence: 99%

“…There are two cations sites (Sr 1 and Sr 2 ) in Sr 2 Si 5 N 8 crystal lattice (Zhang and Yang, 2015). Sr 1 site is ten-coordinated with N atoms where its Sr 1 -N bond has a mean distance of 2.865 Å (Zhang and Yang, 2015; Baginskiy et al , 2011). Meanwhile, Sr 2 site is eight-coordinated to N atoms where its Sr 1 -N bond has a mean distance of 2.928 Å (Zhang and Yang, 2015; Baginskiy et al , 2011).…”

Section: Resultsmentioning

confidence: 99%

“…Sr 1 site is ten-coordinated with N atoms where its Sr 1 -N bond has a mean distance of 2.865 Å (Zhang and Yang, 2015; Baginskiy et al , 2011). Meanwhile, Sr 2 site is eight-coordinated to N atoms where its Sr 1 -N bond has a mean distance of 2.928 Å (Zhang and Yang, 2015; Baginskiy et al , 2011). Sr 1 -N bond, which has shorter bond length and tighter crystal circumstance of Eu 2+ ion, contributes to shorter wavelength and higher energy photon emission [Eu(I)] (Zhang and Yang, 2015; Baginskiy et al , 2011).…”

Section: Resultsmentioning

confidence: 99%

“…Meanwhile, Sr 2 site is eight-coordinated to N atoms where its Sr 1 -N bond has a mean distance of 2.928 Å (Zhang and Yang, 2015; Baginskiy et al , 2011). Sr 1 -N bond, which has shorter bond length and tighter crystal circumstance of Eu 2+ ion, contributes to shorter wavelength and higher energy photon emission [Eu(I)] (Zhang and Yang, 2015; Baginskiy et al , 2011). Meanwhile, Sr 2 -N bond, which has longer bond length and looser crystal circumstance of Eu 2+ ion, contributes to longer wavelength and lower energy photon emission [Eu(II)] (Zhang and Yang, 2015; Baginskiy et al , 2011).…”

Section: Resultsmentioning

confidence: 99%

“…Sr 1 -N bond, which has shorter bond length and tighter crystal circumstance of Eu 2+ ion, contributes to shorter wavelength and higher energy photon emission [Eu(I)] (Zhang and Yang, 2015; Baginskiy et al , 2011). Meanwhile, Sr 2 -N bond, which has longer bond length and looser crystal circumstance of Eu 2+ ion, contributes to longer wavelength and lower energy photon emission [Eu(II)] (Zhang and Yang, 2015; Baginskiy et al , 2011). Figure 6(b) displays configurational coordinates of Eu 2+ ion at high temperature (Majekodunmi, 2015).…”

Section: Resultsmentioning

confidence: 99%

See 3 more Smart Citations

Implementation of phosphor sedimentation to reduce thermal instability issue affecting white LED luminescence

¹

2019

View full text Add to dashboard Cite

Purpose In general, lighting application, white light emitting diode (LED) usually exposed to an extreme operating temperature of above 90°C. It is well-known that luminous efficacy and spectral characteristic of white LED are dependent on the temperature, causing thermal effects on luminous efficacy and color shift of white LED become a critical application checkpoint to be addressed by white LED manufactures. Thus, the purpose of this paper is to minimize the thermal stability issue affecting white LED luminescence during operation by introducing phosphor sedimentation process. Design/methodology/approach The LED samples were assembled and sent for centrifugation with 0, 5 and 10 revolutions per second (rps), respectively, during phosphor sedimentation process. Luminescence properties of these LED samples were then characterized at a varying temperature to investigate the effect of phosphor sedimentation on the luminescence stability of LED samples. The LED samples were also cross-sectioned and analyzed to understand the phosphor sedimentation mechanism. Computational fluid dynamics (CFD) was applied to study the temperature distribution of the non-phosphor sediment (NPS) and phosphor sediment (PS) LED during operation to validate the hypotheses based on experimental data. Findings Experimental results show that the luminous intensity of PS LED samples degrades less significant at high temperature. The experimental results also show that the color coordinate for PS LED samples is more stable and is less blue-shifted than NPS LED samples as the temperature increased. These are because the heat generated by phosphor particles during operation can be dissipated effectively throughout a high thermal conductivity substrate after phosphor sedimentation. Thus, the phosphor temperature of PS LED is lower than NPS LED during operation as validated with the thermal simulation. Practical implications The study of this paper is applicable as a reference for industries who intend to resolve the thermal stability of white LED during operation. The luminescence properties changes as a function of the temperature study in this paper can be used to predict the application performances of white LED accurately. Apart from that, the analysis method of temperature distribution using CFD simulations can be extended by other CFD users in the future. Originality/value Implementation of phosphor sedimentation to reduce thermal instability issue of white LED has yet to be reported on previous studies. Most literature just studied the thermal instability issue of either assembled LED or raw material, without suggesting any solution to tackle the issue.

Luminescence properties and energy transfer studies of color tunable Tb3+-doped RE1/3Zr2(PO4)3 (RE = Y, La, Gd and Lu)

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2016

Journal of Alloys and Compounds

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Effects of the Sr/Ba and Eu2+/Eu3+/Dy3+ ions content on the luminescent emission of M0.90Eu0.1‐xDyxZr4(PO4)6 nanophosphors with M = Sr or Ba and x = 0, 0.025, 0.050 and 0.075

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et al. 2023

Journal of Alloys and Compounds

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No abstract

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