Open Access Research Article Issue
Broadband orange-emitting Sr3Si8O4N10:Eu2+ phosphor discovered by a modified single-particle-diagnosis approach
Journal of Advanced Ceramics 2023, 12 (4): 734-746
Published: 24 March 2023

Discovery of new phosphors with desired properties is of great significance for developing high optical quality solid-state lighting. The single-particle-diagnosis approach is an effective way to search novel phosphors by analyzing tiny single crystals screened from the fired powder mixtures. In this work, a broadband orange-emitting phosphor of Sr3Si8O4N10:Eu2+ for solid state lighting was discovered by this method. The new oxonitridosilicate crystallizes in the monoclinic space group of P21/n (No. 14) with cell parameters of a = 4.8185 Å, b = 24.2303 Å, c = 10.5611 Å, β = 90.616°, and Z = 4. The crystal structure of Sr3Si8O4N10 was determined from the single-crystal X-ray diffraction (XRD) data of a single crystal, which is made up of a three-dimensional framework consisting of vertex-sharing SiN4 and SiN3O tetrahedra. Sr2+ ions occupy five crystallographic sites and have coordination numbers between 6 and 8 with one ordered Sr and other four disordered Sr atoms. The multiple Sr sites lead to a broadband emission centered at 565–600 nm and a bandwidth of 128–138 nm. The internal and external quantum efficiencies (IQE/EQE) of the title phosphor are 48.6% and 29.1% under 450 nm excitation, respectively. To improve the accuracy and speed of distinguishing phosphor particles in fired powder mixtures, a microscopic imaging spectroscopy is developed and demonstrated to modify the single-particle-diagnosis method.

Open Access Research Article Issue
Fine-grained phosphors for red-emitting mini-LEDs with high efficiency and super-luminance
Journal of Advanced Ceramics 2022, 11 (9): 1383-1390
Published: 05 September 2022

Mini-LED backlights, combining color conversion materials with blue mini-LED chips, promise traditional liquid crystal displays (LCDs) with higher luminance, better contrast, and a wider color gamut. However, as color conversion materials, quantum dots (QDs) are toxic and unstable, whereas commercially available inorganic phosphors are too big in size to combine with small mini-LED chips and also have strong size-dependence of quantum efficiency (QE) and reliability. In this work, we prepare fine-grained Sr2Si5N8:Eu2+-based red phosphors with high efficiency and stability by treating commercially available phosphors with ball milling, centrifuging, and acid washing. The particle size of phosphors can be easily controlled by milling speed, and the phosphors with a size varying from 3.5 to 0.7 μm are thus obtained. The samples remain the same QE as the original ones (~80%) even when their particle size is reduced to 3.2–3.5 μm, because they contain fewer surface suspension bond defects. More importantly, SrBaSi5N8:Eu2+ phosphors show a size-independent thermal quenching behavior and a zero thermal degradation. We demonstrate that red-emitting mini-LEDs can be fabricated by combining the SrBaSi5N8:Eu2+ red phosphor (3.5 μm in size) with blue mini-LED chips, which show a high external quantum efficiency (EQE) of above 31% and a super-high luminance of 34.3 Mnits. It indicates that fine and high efficiency phosphors can be obtained by the proposed method in this work, and they have great potentials for use in mini-LED displays.

Open Access Research Article Issue
Composition and structure design of three-layered composite phosphors for high color rendering chip-on-board light-emitting diode devices
Journal of Advanced Ceramics 2021, 10 (4): 729-740
Published: 05 August 2021

A three-layered phosphor structure was designed and prepared by the spin coating of BaSi2N2O2:Eu (cyan-emitting) and (Sr,Ca)AlSiN3:Eu (red-emitting) phosphor films on the yellow- emitting Y3Al5O12:Ce (YAG:Ce) phosphor ceramic synthesized by the solid-state reaction under vacuum sintering. In order to achieve high color rendering lighting, the influence of the composition and structure of the three-layered phosphors on the optical, thermal, and electrical properties of the chip-on-board (COB) packaged white-light-emitting diodes (WLEDs) was studied systematically. The WLED with the structure of "red+cyan+yellow" (R+C+Y) three-layered phosphor generated neutral white light and had a luminous efficacy of 75 lm/W, the fidelity index (Rf) of 93, the gamut index (Rg) of 97, and the correlated color temperature (CCT) of 3852 K. Under the excitation of laser diode (LD), the layer-structured phosphor yielded the white light with a luminous efficacy of 120 lm/W, color rendering index (CRI) of 90, and CCT of 5988 K. The result indicates that the three-layered phosphor structure is a promising candidate to achieve high color rendering and high luminous efficacy lighting.

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