Yayun Zhou

Abstract Near-infrared luminescent materials exhibit unique photophysical properties that make them crucial components in photonic, optoelectronic and biological applications. As broadband near infrared phosphors activated by transition metal elements are already widely reported, there is a challenge for next-generation materials discovery by introducing rare earth activators with 4 f -5 d transition. Here, we report an unprecedented phosphor K 3 LuSi 2 O 7 :Eu 2+ that gives an emission band centered at 740 nm with a full-width at half maximum of 160 nm upon 460 nm blue light excitation. Combined structural and spectral characterizations reveal a selective site occupation of divalent europium in LuO 6 and K2O 6 polyhedrons with small coordination numbers, leading to the unexpected near infrared emission. The fabricated phosphor-converted light-emitting diodes have great potential as a non-visible light source. Our work provides the design principle of near infrared emission in divalent europium-doped inorganic solid-state materials and could inspire future studies to further explore near-infrared light-emitting diodes.

Abstract Phosphor-converted white LEDs rely on combining a blue-emitting InGaN chip with yellow and red-emitting luminescent materials. The discovery of cyan-emitting (470–500 nm) phosphors is a challenge to compensate for the spectral gap and produce full-spectrum white light. Na 0.5 K 0.5 Li 3 SiO 4 :Eu 2+ (NKLSO:Eu 2+ ) phosphor was developed with impressive properties, providing cyan emission at 486 nm with a narrow full width at half maximum (FWHM) of only 20.7 nm, and good thermal stability with an integrated emission loss of only 7% at 150 °C. The ultra-narrow-band cyan emission results from the high-symmetry cation sites, leading to almost ideal cubic coordination for UCr 4 C 4 -type compounds. NKLSO:Eu 2+ phosphor allows the valley between the blue and yellow emission peaks in the white LED device to be filled, and the color-rendering index can be enhanced from 86 to 95.2, suggesting great applications in full-spectrum white LEDs.

Abstract Photoluminescence originated from doped activators in the solid state materials usually faces the challenge of concentration quenching, restricting the further increase of photoluminescence intensity. Herein, a new strategy is demonstrated by the heavy doping Mn 2+ into MgAl 2 O 4 , leading to the broad‐band near‐infrared (NIR) emission peaking at ≈825 nm with a full width at half maximum of ≈125 nm, as well as high internal quantum efficiency of ≈53% upon 450 nm laser excitation. Density functional theory calculation and extend X‐ray absorption fine structure provide a understanding of Al 3+ /Mn 2+ disorder and Mn 2+ –Mn 2+ aggregation in spinel Mg 1–x Al 2 O 4 : x Mn 2+ with high Mn 2+ content, which enables the formation of superexchange coupled IV Mn 2+ – VI Mn 2+ pair. The NIR light‐emitting diodes fabricated by the 450 nm blue chip and Mg 0.50 Al 2 O 4 :0.50Mn 2+ phosphor gives a high NIR output power of ≈78.41 mW under a driven current of 120 mA, and night‐vision application as light source in the dark is demonstrated. This work opens new paths for rational design of efficient broad‐band NIR emitting phosphor, and also provides new insights into the Mn 2+ luminescence and the applications.

Abstract The development of highly efficient and thermally stable broadband near‐infrared (NIR) luminescence materials is a great challenge to advance the next‐generation smart NIR light source. Benefitting from the low phonon energy and relatively weak electron phonon coupling effect of the fluoride, K 2 NaScF 6 :Cr 3+ phosphor is designed and obtained, which demonstrates a full width at half maximum of 100 nm peaking at ≈765 nm. Upon blue light excitation, the phosphor exhibits a high quantum efficiency of 74% and its emission intensity at 150 °C can keep 89.6% of the initial value at 25 °C. An NIR output power of 159.72 mW (input electric power, 1094 mW) with a high photoelectric conversion efficiency of ≈14.60%, light‐emitting diode (LED) device is presented based on this K 2 NaScF 6 :Cr 3+ phosphor. Furthermore, applying the high‐power NIR phosphor‐converted LED device as lighting source, clear and quick veins imaging and recognition in fingers, palm, wrist, and arm of the human hand are first realized, suggesting K 2 NaScF 6 :Cr 3+ phosphor has high promise in practical applications.

Abstract Rapid development of solid-state lighting technology requires new materials with highly efficient and stable luminescence, and especially relies on blue light pumped red phosphors for improved light quality. Herein, we discovered an unprecedented red-emitting Mg 2 Al 4 Si 5 O 18 :Eu 2+ composite phosphor ( λ ex = 450 nm, λ em = 620 nm) via the crystallization of MgO–Al 2 O 3 –SiO 2 aluminosilicate glass. Combined experimental measurement and first-principles calculations verify that Eu 2+ dopants insert at the vacant channel of Mg 2 Al 4 Si 5 O 18 crystal with six-fold coordination responsible for the peculiar red emission. Importantly, the resulting phosphor exhibits high internal/external quantum efficiency of 94.5/70.6%, and stable emission against thermal quenching, which reaches industry production. The maximum luminous flux and luminous efficiency of the constructed laser driven red emitting device reaches as high as 274 lm and 54 lm W −1 , respectively. The combinations of extraordinary optical properties coupled with economically favorable and innovative preparation method indicate, that the Mg 2 Al 4 Si 5 O 18 :Eu 2+ composite phosphor will provide a significant step towards the development of high-power solid-state lighting.