Graphite like C3N4 (g-C3N4) was synthesized facilely via the low temperature thermal condensation of melamine between 300–650°C. The results showed that the products maintained as melamine when the temperature is below 300°C. With the increase of temperature, the products were transformed into carbon nitride and amorphous g-C3N4 successively. The morphology of products was changed from spherical nanoparticles of melamine into layer carbon nitride and g-C3N4 with the increase of temperature. The photoluminescence spectra showed that the carbon nitride products have continuous tunable photoluminescence properties in the visible region with increasing temperature. With the help of steady state, transient state time-resolved photoluminescence spectra and Raman microstructural characterization, a novel tunable photoluminescence mechanism was founded systematically, which is mainly related to the two dimensional π-conjugated polymeric network and the lone pair of the carbon nitride.

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 4f-5d transition. Here, we report an unprecedented phosphor K3LuSi2O7:Eu2+ 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 LuO6 and K2O6 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.

The discovery of high efficiency narrow-band green-emitting phosphors is a major challenge in backlighting light-emitting diodes (LEDs). Benefitting from highly condensed and rigid framework structure of UCr C -type compounds, a next-generation narrow green emitter, RbLi(Li SiO ) :Eu (RLSO:Eu ), has emerged in the oxide-based family with superior luminescence properties. RLSO:Eu phosphor can be efficiently excited by GaN-based blue LEDs, and shows green emission at 530 nm with a narrow full width at half maximum of 42 nm, and very low thermal quenching (103%@150 °C of the integrated emission intensity at 20 °C), however its chemical stability needs to be improved later. The white LED backlight using optimized RLSO:8%Eu phosphor demonstrates a high luminous efficacy of 97.28 lm W and a wide color gamut (107% National Television System Committee standard (NTSC) in Commission Internationale de L'Eclairage (CIE) 1931 color space), suggesting its great potential for industrial applications as liquid crystal display (LCD) backlighting.

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.

Recently developed CsPbX 3 (X = Cl, Br, and I) perovskite quantum dots (QDs) hold great potential for various applications owing to their superior optical properties, such as tunable emissions, high quantum efficiency, and narrow linewidths. However, poor stability under ambient conditions and spontaneous ion exchange among QDs hinder their application, for example, as phosphors in white-light-emitting diodes (WLEDs). Here, a facile two-step synthesis procedure is reported for luminescent and color-tunable CsPbX 3 - zeolite-Y composite phosphors, where perovskite QDs are encapsulated in the porous zeolite matrix. First zeolite-Y is infused with Cs + ions by ion exchange from an aqueous solution and then forms CsPbX 3 QDs by diffusion and reaction with an organic solution of PbX 2 . The zeolite encapsulation reduces degradation and improves the stability of the QDs under strong illumination. A WLED is fabricated using the resulting microscale composites, with CommissionInternationale de I'Eclairage (CIE) color coordinates (0.38, 0.37) and achieving 114% of National Television Standards Committee (NTSC) and 85% of the ITU-R Recommendation BT.2020 (Rec.2020) coverage.

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We report on a red-emitting ScVO4:Bi3+ phosphor which does not show excitation at energies below 2.88 eV (430 nm). X-ray diffraction, time-resolved, and quantitative photoluminescence (PL) spectroscopy were employed to characterize relations between crystal structure and luminescence properties of the material. Results show that incorporation of Bi3+ renders the blue photoemission of blank ScVO4 to red. Dynamic luminescence analysis between 10 and 300 K reveals a complicated dependence of energy transfer from VO4 3– groups to Bi3+ ions and population redistribution of 3P1 and 3P0 of Bi3+ on temperature. This reflects in distinct changes in the luminescence decay functions. That is, a dramatic decrease of Bi3+ luminescence lifetime occurs from hundreds to only several microseconds. Density functional theory is employed to reveal how the unusual red Bi3+ luminescence comes, and results indicate that the perturbation of oxygen vacancies which is generated readily when bismuth precipitates into ScVO4 is the reason for the experimental observation, although the vacancies themselves do not show photoluminescence. Upon excitations at 330 and 380 nm, internal quantum efficiencies can be up to ∼56% and ∼47%, respectively, implying the potential application of the red phosphor in warm-white-light-emitting diodes. As a proof of concept, an exemplary device was developed by combining the present phosphor with an ultraviolet-light-emitting diode and a commercial phosphor (Ba, Eu)MgAl10O17:Mn. We obtain a color rendering index (CRI) of >90 and a color temperature of ∼4306 K at chromaticity (0.3744, 0.3991).

Scintillators with high spatial resolution at a low radiation dose rate are desirable for X‐ray medical imaging. To challenge the state‐of‐art technology, it is necessary to design large‐area wafers with high light yield, oriented light transport, and reduced light scattering. Here, a seed‐crystal‐induced cold sintering is adopted and a <001>‐textured TPP2MnBr4 (TPP: tetraphenylphosphonium) transparent ceramic is fabricated with a large‐area wafer of 5 cm in diameter, exhibiting high optical transparency of above 68% over the 450–600 nm range. The compelling scintillation performance of the TPP2MnBr4 wafer includes a light yield of ≈78 000 ± 2000 photons per MeV, a low detection limit 8.8 nanograys per second, about 625 times lower than the requirement of X‐ray diagnostics (5500 nanograys per second), and an energy resolution of 17% for high‐energy γ‐rays (662 keV). X‐ray imaging demonstrates a high spatial resolution of 15.7 lp mm−1. Moreover, the designed material exhibits good retention of the radioluminescence intensity and light yield. This work presents a paradigm for achieving light‐guiding properties with high transparency and large‐area fabrication by grain orientation engineering, and the transparent, textured metal halide ceramic scintillator is expected to provide a route for advancement in the X‐ray imaging of tomorrow.