In this paper, narrow-band red-emitting SrLiAl3N4:Eu2+ phosphor has been successfully prepared using a solid-state reaction method. The effects of sintering temperatures, times and fluxes on phase formation and luminescence properties are investigated, respectively. The addition of BaF2 flux not only enhances room-temperature emission intensity, but also improves the luminescence thermal stability, which is ascribed to the increase of crystallinity. Under blue light excitation, the as-prepared SrLiAl3N4:Eu2+ phosphor has a narrow emission band with a peak wavelength at ∼648 nm and a full-width at half-maximum of ∼1177 cm−1 (∼50 nm). The critical quenching concentration of Eu2+ is about 1 mol%. White light-emitting-diode (w-LED) devices have been fabricated which are obtained by combining a 455 nm chip with the commercial yellow phosphor and the present red phosphor. The results exhibit a potential application for phosphor-converted LEDs (pc-LEDs).
The thermal quenching property of phosphors has been proven to have a strong impact on the application of them. In this paper, a series of (Ba1−xSrx)2SiO4:Eu2+ compounds have been synthesized via conventional high-temperature solid-state reaction. Based on the Rietveld fitting analysis of the X-ray diffraction data, the preferential occupancy behavior of Sr2+/Ba2+ ions is verified. We adopt the cation ordering to characterize this preferential occupancy and find that the degree of cation ordering reaches its maximum at x=0.5 and decreases as x deviates from 0.5. The photoluminescence measurements show that the intermediate composition (x=0.5) exhibits the best luminescence thermal stability with T1/2 over 200 °C. The composition dependence of thermal quenching temperature is well similar to the composition dependence of the degree of cation ordering, indicating that the thermal quenching property of (Ba1−xSrx)2SiO4:Eu2+ is positively related to the cation ordering. This work provides a deeper understanding between thermal quenching properties and crystal structures of phosphors.
Red-emitting nitride phosphors excited with blue light have great potential for the fabrication of warm white light-emitting diodes (WLEDs). Chemical composition and structural modification are generally adopted to optimize the photoluminescence behaviors of the targeted phosphors. Herein, on the basis of the famous CaAlSiN3 phosphors, Eu2+-doped (Ca1–xLix)(Al1–xSi1+x)N3 solid solutions via the cations’ cosubstitution of (CaAl)5+ pair by (LiSi)5+ pair are successfully synthesized by a solid state reaction, and the lattice parameters show a linear decrease with chemical compositions suggesting the formation of the isostructural phase relationship. Four types of coordinated structure models, corresponding to different coordination environments of Eu2+, are proposed over the course of structural evolution, which induces different structural rigidity and stability, and then they are responsible for three-stage changes of emission spectra of Eu2+ in (Ca1–xLix)(Al1–xSi1+x)N3 solid solution.
This paper focuses on the stability and consistency of intensity measurements of WLED phosphors. The quality of phosphor products are determined by the measured intensities, but in practice it is often found that intensity measurements cannot be replicated. This problem is due to the instability of test conditions (fluctuating light source power, different paring of quartz lids, etc.) A Monte Carlo ray-tracing model is applied to illustrate the differences in faculae caused by tiny quartz lid slips. The research presented would be particularly beneficial for researchers and manufactures of phosphor.
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