Recent progress on discovery of novel phosphors for solid state lighting

The trade-off anionic modulation in metal-organic glasses showing color-tunable persistent luminescence

Ultralong room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) materials provide exciting opportunities for the rational design of persistent luminescence owing to their long-lived excitons. However, conventional rare-earth-based all-inorganic emitters involve high cost and harsh synthesis conditions, and purely organic systems may require complicated synthesis routes and tedious purification. Therefore, it is highly desirable to develop a cost-effective and easily manufacturable method for achieving color-tunable RTP-TADF with a long afterglow. Herein, we demonstrate a rational strategy to introduce different anions (Cl-, Br- and OAc- ions) into a Zn-based metal-organic scaffold, which can improve the crystal rigidity and achieve a well-balanced RTP-TADF. Both theoretical and experimental studies have demonstrated that the adjustment of different anions can effectively modulate the spin-orbit coupling (SOC) and the energy gap of singlet-triplet states (ΔEST) and then tailor the afterglow lifetime. Moreover, we prepared dye-doped metal-organic hybrid glasses with remarkable potential for the color-tunable afterglow. Therefore, this work not only provides a new horizon for modulating crystal and glass states with color/lifetime-tunable persistent luminescence, but also contributes to optical information storage and anti-counterfeiting technology.

Synthesis of Eu3+-Doped NaGd9Si6O26 Sub-Microcrystals from a NaGdF4@SiO2 Structure

Rare earth silicate phosphors of high quantum efficiency with a stable performance are promising materials in the fields of display and illumination. The grain sizes of products synthesized via the conventional solid-state reaction method are usually too large to satisfy the requirements of color cast and extraction efficiency in high-resolution light-emitting devices (LEDs). We designed a synthetic route and successfully fabricated rare earth silicate NaGd₉Si₆O₂₆ (NGSO) sub-microcrystals with a size ranging from 550 to 1200 nm. The reaction mechanism and optical properties were systematically investigated. The quantum efficiency of Eu³⁺-activated NGSO sub-microcrystals was about 36.6%. The LED encapsulated with these sub-microcrystals showed lower color deviation and higher lumen efficiency and lumen flux compared to that with NGSO fabricated using the conventional solid state reaction method.

Realizing near white and warm light emission of cuprous iodide complexes by alkyl-isomerization of ligands

Four novel all-in-one structured cuprous iodide hybrid materials are presented. Isomerization of the alkyl chain on the ligand improved material thermal stability and regulated their luminescence to warm and near-white light emission, with the internal quantum yield increasing from 5% to 83%. This provides a reasonable route for designing white light emitting cuprous iodide materials for solid-state lighting in future.

Design of a nitridoalumosilicate red phosphor synthesized under mild conditions

A nitridoalumosilicate red phosphor Ca4SiAl3N7:Eu2+ was successfully synthesized at normal pressure and a low temperature (1350 °C).

Novel narrow-band blue light-emitting phosphor of Eu2+-activated silicate used for WLEDs

Owing to the broad application scope of phosphors for light and display, the development of narrow-band light-emitting phosphors has recently gained considerable research attention. In this study, a new type of narrow-band blue light-emitting phosphor, Rb₂HfSi₃O₉:Eu²⁺, with a full width at half maximum (FWHM) of 64 nm was synthesized successfully. Upon the near visible ultraviolet (NUV) light excitation, the internal quantum efficiency of Rb₂HfSi₃O₉:Eu²⁺ was 68%. It also exhibited good thermal stability, which was higher than that of a commercial blue phosphor (BaMgAl₁₀O₁₇:Eu²⁺) at 150 °C. The significant photoluminescence properties of Rb₂HfSi₃O₉:Eu²⁺ were found to be related to its robust crystal structure, which was investigated in detail. The results indicate that Eu²⁺-activated Rb₂HfSi₃O₉ is a promising phosphor for use in white light-emitting diodes.

Broadband NaK2Li[Li3SiO4]4:Ce Alkali Lithosilicate Blue Phosphors

Phosphors with a rigid and symmetrical structure are urgently needed. The alkali lithosilicate family (A[Li₃SiO₄]) has been extensively studied with a narrow emission band due to its unique cuboid-coordinated environment and rigid structure. However, here we demonstrate for the first time Ce-doped NaK₂Li[Li₃SiO₄]₄ phosphors with a broad emission band, a high internal quantum efficiency (85.6%), and excellent thermal stability. Photoluminescence indicates the Ce's preference to occupy the Na⁺ site, leading to a strong blue color emission with peak maxima at 417 and 450 nm. Temperature- and pressure-dependent photoluminescence reveals thermal stability and a phase transition. Moreover, the X-ray absorption near-edge structure reveals the mixing of Ce³⁺ and Ce⁴⁺ in the materials; this result differs from that of Eu²⁺-doped A[Li₃SiO₄] phosphors. The charge compensation process is then proposed to explain this difference. This study not only provides insights into Ce-doped UCr₄C₄-type phosphors but also explains the charge compensation mechanism of the aliovalent doping process.