Luminescence properties of red-emitting M2Si5N8:Eu2+ (M=Ca, Sr, Ba) LED conversion phosphors

mentioning

confidence: 80%

Persistent luminescence in rare-earth codoped

Eeckhout

Smet

Poelman

2009

“…This observation indicates to a relatively large covalency of the metal-oxygen bond in Li 2 SrSiO 4 . It is interesting to compare the results with the literature data for lanthanide (Ln¼Ce 3 + , Eu 2 + )-doped alkalineearth silicon nitrides of the composition M 2 Si 5 N 8 (M ¼Ca, Sr), since these materials were found to have a high potential for white LED's applications [25,26]. It is seen that the values of E cfs for Ce 3 + in M 2 Si 5 N 8 (13,000-15,000 cm À 1 [27]) are essentially smaller than that for Li 2 SrSiO 4 :Ce 3 + .…”

Section: What Factors Cause the Long-wavelength Position Of The Eu 2 mentioning

confidence: 94%

“…It is seen that the values of E cfs for Ce 3 + in M 2 Si 5 N 8 (13,000-15,000 cm À 1 [27]) are essentially smaller than that for Li 2 SrSiO 4 :Ce 3 + . The very large values of E c ( $ 20,000 cm À 1 ) indicate that the long-wavelength emissions of Ce 3 + (and Eu 2 + too) in M 2 Si 5 N 8 (M¼Ca, Sr) [26,27] should be attributed to the high degree of covalency of the Ln-N bond. In contrast to Ln-doped M 2 Si 5 N 8 , the influence of the crystal structure of Li 2 SrSiO 4 on spectral position of the Eu 2 + emission maximum is explained as arising from the both contributions, the large crystal field splitting of the 4f 6 5d configuration and the covalency effect.…”

Section: What Factors Cause the Long-wavelength Position Of The Eu 2 mentioning

confidence: 99%

Luminescent properties of Eu2+ and Ce3+ ions in strontium litho-silicate Li2SrSiO4

Dotsenko¹,

Levshov²,

Berezovskaya³

et al. 2011

a b s t r a c tThe luminescent properties of Eu 2 + and Ce 3 + ions in Li 2 SrSiO 4 have been studied upon excitation in the 2-20 eV region. Based on the results of luminescent measurements, values of the crystal field splitting and the centroid shift of the Ce 3 + 5d configuration in Li 2 SrSiO 4 were found and compared with those of Ce 3 + ions in some other inorganic compounds. The Eu 2 + ions in Li 2 SrSiO 4 exhibit a broad band emission with a maximum at 576 nm, which is due to the 4f 6 5d-4f 7 transition. It was shown that the long-wavelength position of the Eu 2 + emission in Li 2 SrSiO 4 is caused by the large crystal-field splitting of the Eu 2 + 4f 6 5d configuration and relatively high degree of covalency of the Eu-O bond. The stabilization of Eu 2 + ions in Li 2 SrSiO 4 during the synthesis process requires a strong reducing agent. Two phenomenological approaches to explain the low stability of Eu 2 + in Li 2 SrSiO 4 are also discussed.

“…Based on the rather large width of the emission band in M 2 Si 5 N 8 :Eu it was suggested that this could be due to the different sites [11]. Consequently, the TL peaks might be broadened due to similar defects being in the proximity of both europium sites, thus possibly having slightly different trap depths.…”

Section: Thermoluminescence Excitation Contour Plotsmentioning

confidence: 99%

“…Recently, the family of alkaline earth nitrido-silicates, M 2 Si 5 N 8 :Eu (M = Ca, Sr, Ba) and their Tm-codoped variants were studied [10]. These materials are much more stable than the aforementioned sulfides and show a high quantum efficiency, which has led to extensive research into their use as conversion phosphors in white LEDs [11,12,[18][19][20][21][22][23][24][25][26][27][28]. Recently, orange and reddish persistent luminescence was reported in these compounds, most notably in Ca 2 Si 5 N 8 :Eu,Tm [10,13,14,18,29,30].…”

Section: Introductionmentioning

confidence: 99%

Temperature and wavelength dependent trap filling in M2Si5N8:Eu (M=Ca, Sr, Ba) persistent phosphors

Smet¹,

Eeckhout²,

Bos³

et al. 2012

The evaluation of persistent phosphors is often focused on the processes right after the excitation, namely on the shape of the afterglow decay curve and the duration of the afterglow, in combination with thermoluminescence glow curve analysis. In this paper we study in detail the trap filling process in europium-doped alkaline earth silicon nitrides (Ca 2 Si 5 N 8 :Eu, Sr 2 Si 5 N 8 :Eu and Ba 2 Si 5 N 8 :Eu), i.e., how the persistent luminescence can be induced. Both the temperature at which the phosphors are excited and the spectral distribution of the excitation light on the ability to store energy in the phosphors' lattices are investigated. We show that for these phosphors this storage process is thermally activated upon excitation in the lower 5d excited states of Eu 2+ , with the lowest thermal barrier for europium doped Ca 2 Si 5 N 8 . Also, the influence of co-doping with thulium on the trap filling and afterglow behavior is studied. Finally there exists a clear relation between the luminescence quenching temperature and the trap filling efficiency. The latter relation can be utilized to select new efficient 5d-4f based afterglow phosphors. 2 Center for Nano-and Biophotonics (NB-Photonics), Ghent University, Belgium.