Carbon nanostructures are attracting intense interest because of their many unique and novel properties. The strong and tunable luminescence of carbon materials further enhances their versatile properties; in particular, the quantum effect in carbon is extremely important both fundamentally and technologically. [1][2][3][4] Recently, photoluminescent carbonbased nanoparticles have received much attention. They are usually prepared by laser ablation of graphite, electrochemical oxidation of graphite, electrochemical soaking of carbon nanotubes, thermal oxidation of suitable molecular precursors, vapor deposition of soot, proton-beam irradiation of nanodiamonds, microwave synthesis, and bottom-up methods.[5-13] Although small (ca. 2 nm) graphite nanoparticles show strong blue photoluminescence (PL), [13] definitive experimental evidence for luminescence of carbon structure arising from quantum-confinement effects and size-dependent optical properties of carbon quantum dots (CQDs) remains scarce.Herein, we report the facile one-step alkali-assisted electrochemical fabrication of CQDs with sizes of 1.2-3.8 nm which possess size-dependent photoluminescence (PL) and excellent upconversion luminescence properties. Significantly, we demonstrate the design of photocatalysts (TiO 2 /CQDs and SiO 2 /CQDs complex system) to harness the use of the full spectrum of sunlight (based on the upconversion luminescence properties of CQDs).

Größenkontrolliert: Eine einstufige Alkalimetall‐unterstützte elektrochemische Methode zur Herstellung von Kohlenstoff‐Quantenpunkten (CQDs) mit größenabhängiger Lumineszenz wird vorgestellt (siehe Bild). Die Upconversion‐Lumineszenz der CQDs könnte als Grundlage für die Entwicklung neuer Photokatalysatoren dienen.

Due to the unique narrow-band red emission and broadband blue light excitation, as well as milder synthesis conditions, Mn 4+ ion activated fluoride red phosphors show great promise for white light emitting diode (W-LED) applications. However, as the Mn 4+ emission belongs to a spin-forbidden transition ( 2 E g → 4 A 2 ), it is a fundamental challenge to synthesize these phosphors with a high external quantum efficiency (EQE) above 60%. Herein, a highly efficient and thermally stable red fluoride phosphor, Cs 2 SiF 6 :Mn 4+ , with a high internal quantum efficiency (IQE) of 89% and ultrahigh EQE of 71% is demonstrated. Furthermore, nearly 95% of the room-temperature IQE and EQE are maintained at 150 °C. The static and dynamic spectral measurements, as well as density functional theory (DFT) calculations, show that the excellent performance of Cs 2 SiF 6 :Mn 4+ is due to the Mn 4+ ions being evenly distributed in the host lattice Cs 2 SiF 6 . By employing Cs 2 SiF 6 :Mn 4+ as a red light component, stable 10 W high-power warm W-LEDs with a luminous efficiency of ∼110 lm/W could be obtained. These findings indicate that red phosphor Cs 2 SiF 6 :Mn 4+ may be a highly suitable candidate for fabricating high-performance high-power warm white LEDs.

For phosphor-converted white LEDs based on UV chips, it is essential to search high efficient phosphors that better feature with broadly tunable emission and particularly have no or less excitation in visible ranges.

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