The red persistent luminescence of (Sr,Ca)AlSiN3:Eu2+ and mechanism different to SrAl2O4:Eu2+,Dy3+

Journal of Luminescence, April 2019, 208

(Sr,Ca)AlSiN3:Eu²⁺ phosphors have been widely used in phosphor-converted white light emitting diodes. Herein, we reported the strong red persistent luminescence in (Sr,Ca)AlSiN3:Eu²⁺ under UV light excitation. The Sr0.8Ca0.2AlSiN3:0.15% Eu²⁺ shows the strongest red persistent luminescence with a peak emission wavelength at ~628 nm and a persistent time of ~9600 s at the 0.32 mcd/m² threshold value. A new persistent luminescence mechanism, which is different to that of SrAl2O4:Eu²⁺,Dy³⁺, was proposed by comparing the thermoluminescence excitation spectrum (TLES) and the photoluminescence excitation spectrum (PLES) of Sr0.8Ca0.2AlSiN3:0.15% Eu²⁺. The electrons are directly excited from 4f ground states to the conduction band or from valence band to conduction band in (Sr,Ca)AlSiN3:Eu²⁺; while, in SrAl2O4:Eu²⁺,Dy³⁺, they are first excited to 5d level and then stimulated thermal process to the conduction band. The effect of Eu²⁺ concentration on red persistent luminescence in (Sr,Ca)AlSiN3:Eu²⁺ were discussed. The proposed mechanism of persistent luminescence can help us to design and find new persistent luminescence materials.

Effects of full-range Eu concentration on Sr2-2xEu2xSi5N8 phosphors: A deep-red emission and luminescent thermal quenching

Journal of Alloys and Compounds, Volume 770, 5 January 2019, Pages 1069-1077

To fabricate white-light-emitting diodes (white LEDs) with high color-rendering index or full light spectrum emission, the discovery of more efficient deep-red emitting phosphor materials is essential. In this paper, we have synthesized a series of Sr2-2xEu2xSi5N8 (0 ≤ x ≤ 1) solid-solution compounds, and have systemically investigated effects of full-range Eu concentration on their luminescence. Their emission band maximum can be largely tuned from 610 to 725 nm by increasing Eu content. Reabsorption at low Eu2+ concentration while both the energy transfer and Stocks shift at high Eu2+ concentration account for this large spectral red-shift. Luminescent thermal quenching performance gets worse with Eu2+ concentration increasing. The compound with x = 0.15 possesses the best crystallinity and the highest luminescence intensity with the peak position around 660 nm, and still maintains 88.5% room-temperature intensity at 400 K, indicating that great potential for the application as a deep-red phosphor.

    5d-level centroid shift and coordination number of Ce3+ in nitride compounds

    Journal of Luminescence 200 (2018) 35–42

    Energy of 5d-levels of Ce3+ in numerous nitrides has become available due to the development of nitride phosphors recently. In this work, we have collected data on 5d-levels of Ce3+ and reconsidered the 5d centroid shift of Ce3+ in nitrides. The uniform standard, derived from the bond valence theory and the requirement for the high stability of the coordination polyhedron, has been proposed to determine the coordination number. The relationship between the 5d centroid shift of Ce3+, the polarizability of the anions and the electronegativity of the cations is revealed. The anion polarizability is linearly related to the inverse square of the average electronegativity of the cations; and the 5d centroid shift of Ce3+ can be well predicted by virtue of crystallographic data. This paper provides a feasibility to predict luminescence properties of Ce3+-doped nitrides.