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Glycolaldehyde (HOCH2CHO, GA), the simplest molecule containing both hydroxyl and aldehyde groups, is structurally the most elementary member of monosaccharide sugars, which may provide new clues for probing the origin of life on planets like the Earth. Uncovering the existing state of GA in solution systems is an important scientific issue. Generally, methanol is used as the main mobile phase in the liquid chromatography analysis of GA, but the state of GA existing in methanol solution remains unknown, thus making it difficult to analyse GA accurately. Herein, the state and dynamic equilibrium of GA in methanol solution were systematically studied by UV-visible spectroscopy, nuclear magnetic resonance (1H-NMR) spectroscopy, liquid chromatography mass spectrometry (LC–MS) and density functional theory (DFT) calculations. The results demonstrated that the equilibrium component of GA in methanol solution is different from that in aqueous solution and that glycolaldehyde hemiacetal (GAHA) is a dominant component (>90%). Laying the foundation for experimental analysis, the transformation of different components at equilibrium was studied using DFT. The results confirm that hydrogen bonding-induced proton transfer occurs between the components at equilibrium. This work provides an important reference for the analysis of sugars and related compounds in various biochemical reactions. [ABSTRACT FROM AUTHOR]

We report a combination of experimental and computational mechanistic studies for the photoreduction of CO2 to CO with water, catalyzed by single-atom Fe supported on graphitic carbon nitride (g-C3N4). Density functional theory (DFT) and time-dependent DFT (TDDFT) methods were utilized to explore the behavior of single-atom Fe in g-C3N4, which is of vital importance to the understanding of the CO2 reduction reaction (CO2RR) mechanism. The calculation results reveal that the rate-limiting step of the hydrogen-bonded complex in the absence of Fe atoms is the cleavage of C–O bonds in COOH radicals during the whole CO2RR, which includes the photophysical and photochemical processes. The presence of Fe atoms not only activated CO2 in the ground state and increased the rate constant of the limiting step in the photophysical process, but also functioned as the catalytic active center, lowering the reaction barrier of the C–O bond cleavage in COOH˙ in the photochemical process and resulting in improved photocatalytic activity. In addition, DFT calculations further demonstrated that the electron and proton transfer involved in the photophysical and photochemical processes is closely related to and induced by the hydrogen bonds in the excited state. [ABSTRACT FROM AUTHOR]

White light-emitting diodes (WLEDs) have been considered as the next generation lighting technology due to their advantages such as high efficiency and environmental friendliness. However, current mainstream WLEDs, which are based on blue chips and the Y3Al5O12:Ce3+ yellow phosphor, suffer from the problem of low color rendering index (CRI). To solve this problem, a yellowish-green phosphor Ca1.5Y1.5Al3.5Si1.5O12:Ce3+ (CYAS:Ce3+) based on the garnet structure has been designed in this study. Its crystal structure, band structure, and luminescence properties have been investigated in detail. CYAS:Ce3+ exhibits efficient and thermal-stable yellowish-green emission. The 5d centroid shift and crystal splitting of the Ce3+ ion in CYAS have been analyzed together with the structure. Moreover, good warm white light with a low correlated color temperature (3210 K), high color rendering index (85.1) and luminous efficacy (88.5 lm W−1) has been obtained by combining CYAS:Ce3+ and the red phosphor CaAlSiN3:Eu2+ with a blue LED chip. [ABSTRACT FROM AUTHOR]

The interaction between a luminescent covalent organic framework (COF) and the indoor pollutant NH3 was investigated based on density functional theory and time-dependent density functional theory. The frontier molecular orbitals and electronic configuration showed that the luminescence mechanism of the COF was strongly affected by the hydrogen bond between the COF and NH3. In addition, the calculated hydrogen bond length, infrared (IR) spectra, and proton nuclear magnetic resonance (1H NMR) spectroscopy analysis indicated that the hydrogen bond in the S1 state was enhanced, which is identical to the calculated results of electronic excitation energies. The fluorescence rate coefficient of the COF was reduced when interacting with NH3. The hydrogen bond between the COF and NH3 in the S1 state is critical for the COF luminescence properties, which means that the COF shows potential application in the detection of NH3. [ABSTRACT FROM AUTHOR]

The interaction between a luminescent covalent organic framework (COF) and the indoor pollutant NH3 was investigated based on density functional theory and time-dependent density functional theory. The frontier molecular orbitals and electronic configuration showed that the luminescence mechanism of the COF was strongly affected by the hydrogen bond between the COF and NH3. In addition, the calculated hydrogen bond length, infrared (IR) spectra, and proton nuclear magnetic resonance (1H NMR) spectroscopy analysis indicated that the hydrogen bond in the S1 state was enhanced, which is identical to the calculated results of electronic excitation energies. The fluorescence rate coefficient of the COF was reduced when interacting with NH3. The hydrogen bond between the COF and NH3 in the S1 state is critical for the COF luminescence properties, which means that the COF shows potential application in the detection of NH3. [ABSTRACT FROM AUTHOR]

In widely used phosphor-converted white-light-emitting diodes, thermal stability is one of the key indexes for phosphors. It not only implies that the emission intensity should remain unchanged, but also requires a steady peak pattern and position when the phosphors work at varying temperatures. For realizing excellent thermal stability, the thermal behaviors of various phosphors have been discussed and clearly explained in this review article, which focuses on single-doped Ce3+ or Eu2+ or co-doped oxides, oxynitrides, and nitride-based phosphors. These results indicate that the luminescence properties of different phosphors would show abundant changes under varying temperatures, which mainly relies on the crystal structure of the host. By analyzing the relationship between the thermal behavior and host lattice of the phosphors in different matrixes, it has been concluded that a rigid crystal structure combined with a symmetric site is the precondition for phosphors to realize excellent thermal stability; therefore, this work summaries various types of systems with a rigid framework and several ways to prevent phosphors from undergoing thermal disturbances. This provides a research direction toward exploring new and stable phosphors and ways to improve the thermal stability of existing phosphors. [ABSTRACT FROM AUTHOR]

In recent years, the rare-earth elements in white light-emitting phosphors have a problem of increased demand and high price. To overcome these disadvantages, defects have been considered to act as new efficient luminescent centers to replace rare-earth elements. In this work, a rare-earth free self-activated orange light emitting phosphor of single-phase magnesium boron nitride, Mg3BN3, was successfully designed and synthesized by a relatively simple solid-state reaction. Its crystal structure and electronic structure have been measured using Rietveld refinement on the basis of X-ray diffraction data and density functional theory (DFT). The results show that Mg3BN3 crystallizes in a centrosymmetric hexagonal phase with plenty of N=B=N double bonds and has a direct bandgap. The SEM and TEM images and Raman spectra exhibit the sample's good dispersibility and great crystallinity. Under excitation at 397 nm, a broad emission band with orange light emission peaked at 617 nm can be obtained. It is speculated to result from the defect energy levels formed by vacancies, which can also lead to tunability of the emission peak at about 100 nm. The thermal quenching shows that Mg3BN3 at 200 °C still has more than 40% of the initial intensity at room temperature. All these results indicate that the self-activated light emitting phosphors of Mg3BN3 are a potential candidate for n-UV LED applications. [ABSTRACT FROM AUTHOR]

A novel garnet phosphor, Ca2LuHf2(AlO4)3:Ce3+ (CLHA:Ce3+), was successfully designed and synthesized using a solid-state method. Its crystal structure, band structure and photoluminescence properties were investigated in detail. Under n-UV excitation, CLHA:Ce3+ exhibited cyan to blue-green emission depending on the Ce3+ concentration. The QE of the optimal sample was 50.3%. The concentration quenching mechanism of the Ce3+ emission was dominated by dipole–dipole interactions. A novel method to obtain white light was developed by combining the CLHA:Ce3+ phosphor with a CaAlSiN3:Eu2+ red phosphor. Both the emission intensity and thermal stability of CLHA:Ce3+ were found to be superior to those of the commercial (Sr,Ba)2SiO4:Eu2+ phosphor. All of the results indicate the CLHA:Ce3+ phosphor to be a promising candidate for application in white LEDs. [ABSTRACT FROM AUTHOR]

We exhibit a vivid example of turning waste into treasure for the development of persistent luminescence (PersL) phosphor. Facing the original experimental failure in which the as-synthesized Ca2Ga2SiO7:Pr3+,Yb3+ phosphor showed very weak PersL, we did not give up but made a deep analysis. It reveals that the relatively deep depth of traps (0.72 eV) may be the key reason for the weak PersL of Ca2Ga2SiO7:Pr3+,Yb3+ phosphor. Accordingly, in order to make the depth of the traps more shallow, a band gap engineering method was applied by the partial substitution of Si4+ with Ge4+ ions. Investigation into the optical spectra and the electronic structures indicate that the band gap has been successfully reduced. Correspondingly, the depth of traps becomes shallower, and it is adjusted in an appropriate range (around 0.65 eV) when Si : Ge = 1 : 9. As a consequence, the original “waste” phosphor with very weak PersL is successfully turned into a valuable PersL phosphor: Ca2Ga2(Si0.1Ge0.9)O7:Pr3+,Yb3+, whose PersL duration time and initial PersL brightness have been increased by 74 times and 52 times, respectively, compared with the original Ca2Ga2SiO7:Pr3+,Yb3+ sample. [ABSTRACT FROM AUTHOR]

A novel blue-emitting phosphor Na3Sc2(PO4)3:Eu2+ was successfully synthesized by solid-state reaction. The crystal structure, bandgap, and photoluminescence properties were investigated in detail. Under n-UV excitation, the NSP:Eu2+ phosphor exhibits a narrow blue emission peaking at 458 nm with a FWHM of about 50 nm. The concentration quenching mechanism of the NSP:Eu2+ is dominated by the dipole–dipole interaction. Moreover, the NSP:Eu2+ shows better PL intensity, colour purity and thermal quenching properties compared to the commercial BAM phosphor. Non-equivalence replacement of Eu2+ ions for Na+ ions causing defects, inducing the abnormal thermal quenching behaviour. All these results suggest that the NSP:Eu2+ phosphor can be a potential candidate for n-UV LED applications. [ABSTRACT FROM AUTHOR]

A series of SrSiAl2O3N2:Eu2+ (0.005 ≤x≤ 0.05) phosphors were successfully synthesized through a pressureless, facile, and efficient solid state route. The crystal structure, band structure, and their photoluminescence and cathodoluminescence properties were investigated in detail. The phosphors exhibit rod shape morphology with a uniform Eu2+ distribution. Under n-UV excitation the emission spectra shift from 477 to 497 nm with an increase of Eu2+ concentration. The concentration quenching mechanism of Eu2+ emission was dominated by the dipole–dipole interaction. The thermal stability is comparable to that of the commercial Ba2SiO4:Eu2+ phosphor. The phosphor also exhibits high current saturation and high resistance under low voltage electron bombardment. All the results indicate that the SrSiAl2O3N2:Eu2+ phosphors can be considered as candidates for application in both white LEDs and FEDs. [ABSTRACT FROM AUTHOR]

The promising green oxynitride phosphor, Ba3−xMgxSi6O12N2:Eu2+ was synthesized by the solid-state reaction method. The effect of Mg2+ doping on the structure and photoluminescence (PL) properties of Ba3Si6O12N2:Eu2+ was investigated systematically. The results reveal that the phosphor retains the single phase of Ba3Si6O12N2, with the lattice expanding upon increasing the Mg2+ concentration, in an appropriate range. This suggests that a large portion of Mg2+ enters into the interstitial sites of the crystal lattice. At a certain concentration, Mg2+ doping can greatly enhance the absorption and PL intensity and decrease the full widths at half maximum (FWHM) of Ba3Si6O12N2:Eu2+ phosphors. The green phosphor Ba2.87Eu0.1Mg0.03Si6O12N2 exhibited a small thermal quenching, which remained 82% of the initial emission intensity when measured at 150 °C. The quantum efficiency measured at 400 nm excitation was 38.5%. All the results indicate that the solid solution Ba3−xMgxSi6O12N2:Eu2+ can be a good candidate for phosphors applicable in n-UV LEDs for solid-state lighting. [ABSTRACT FROM AUTHOR]

A green-emitting nitride phosphor Ca1.4Al2.8Si9.2N16:Ce3+, Li+ (CASN:Ce) has been successfully synthesized which is applicable to near-ultraviolet based light-emitting diodes (LEDs) and field emission displays (FEDs). The characteristic photoluminescence (PL) properties were studied in detail by PL excitation, emission spectra and time-resolved spectroscopy. CASN:0.10Ce exhibits broad-band green emission centered at ∼525 nm (FWHM ≈ 135 nm) under 395 nm excitation and with excellent thermal stability. The effect of host lattice composition on PL properties was also discussed. The cathodoluminescence (CL) spectra as a function of accelerating voltage and probe current were also studied. Excellent degradation resistance properties with good color stability were obtained by continuous low-voltage electron-beam excitation of the phosphor. [ABSTRACT FROM AUTHOR]

A near-UV excited phosphor, Y4Si2O7N2:Ce3+, was synthesized using a solid-state reaction. The crystal structure and luminescence properties were studied. Y4Si2O7N2 crystallizes in a monoclinic unit cell with space group P21/c, lattice constants a = 7.5678(2) Å, b = 10.4529(1) Å, c = 10.7779(3) Å and β = 110.06°, and cell volume = 800.85(2) Å3. The crystal structure of Y4Si2O7N2, featuring Si(O,N)4 polyhedra, is provided, and there are four different Y3+ coordination environments with two different coordination numbers in the structure. Ce3+-doped Y4Si2O7N2 exhibited a broad emission band, and the maximum emission wavelength could be tuned from blue (λem = 450 nm) to green (λem = 515 nm) by increasing the concentration of Ce3+. The quantum efficiency was determined to be about 47%. The results show that Y4Si2O7N2:Ce3+ is a candidate for use as a conversion phosphor for near-UV white LED applications. [ABSTRACT FROM AUTHOR]

A series of quaternary nitride solid solutions with a general formula of Sr1−xCaxYSi4N7:Eu2+ (1 atom%) were synthesized by the carbothermal reduction and nitridation (CRN) method. The XRD patterns confirm the formation of a solid solution of Sr1−xCaxYSi4N7:Eu2+ (0 ≤x≤ 0.5). With an increase in x, the emission spectra shift from 540 nm to 564 nm under n-UV excitation. In addition, the temperature dependence of the PL intensity was investigated. The thermal stability is comparable to that of the commercial (Ba,Sr)2SiO4:Eu2+ phosphor. All the results indicate that the solid solution Sr1−xCaxYSi4N7:Eu2+ can be a good candidate of phosphor applicable to n-UV LEDs for solid-state lighting. [ABSTRACT FROM AUTHOR]

We report a combination of experimental and computational mechanistic studies for the photoreduction of CO 2 to CO with water, catalyzed by single-atom Fe supported on graphitic carbon nitride (g-C 3 N 4 ). Density functional theory (DFT) and time-dependent DFT (TDDFT) methods were utilized to explore the behavior of single-atom Fe in g-C 3 N 4 , which is of vital importance to the understanding of the CO 2 reduction reaction (CO 2 RR) mechanism. The calculation results reveal that the rate-limiting step of the hydrogen-bonded complex in the absence of Fe atoms is the cleavage of C-O bonds in COOH radicals during the whole CO 2 RR, which includes the photophysical and photochemical processes. The presence of Fe atoms not only activated CO 2 in the ground state and increased the rate constant of the limiting step in the photophysical process, but also functioned as the catalytic active center, lowering the reaction barrier of the C-O bond cleavage in COOH˙ in the photochemical process and resulting in improved photocatalytic activity. In addition, DFT calculations further demonstrated that the electron and proton transfer involved in the photophysical and photochemical processes is closely related to and induced by the hydrogen bonds in the excited state.

In recent years, the rare-earth elements in white light-emitting phosphors have a problem of increased demand and high price. To overcome these disadvantages, defects have been considered to act as new efficient luminescent centers to replace rare-earth elements. In this work, a rare-earth free self-activated orange light emitting phosphor of single-phase magnesium boron nitride, Mg 3 BN 3 , was successfully designed and synthesized by a relatively simple solid-state reaction. Its crystal structure and electronic structure have been measured using Rietveld refinement on the basis of X-ray diffraction data and density functional theory (DFT). The results show that Mg 3 BN 3 crystallizes in a centrosymmetric hexagonal phase with plenty of N[double bond, length as m-dash]B[double bond, length as m-dash]N double bonds and has a direct bandgap. The SEM and TEM images and Raman spectra exhibit the sample's good dispersibility and great crystallinity. Under excitation at 397 nm, a broad emission band with orange light emission peaked at 617 nm can be obtained. It is speculated to result from the defect energy levels formed by vacancies, which can also lead to tunability of the emission peak at about 100 nm. The thermal quenching shows that Mg 3 BN 3 at 200 °C still has more than 40% of the initial intensity at room temperature. All these results indicate that the self-activated light emitting phosphors of Mg 3 BN 3 are a potential candidate for n-UV LED applications.

A series of SrSiAl2O3N2:Eu(2+) (0.005 ≤x≤ 0.05) phosphors were successfully synthesized through a pressureless, facile, and efficient solid state route. The crystal structure, band structure, and their photoluminescence and cathodoluminescence properties were investigated in detail. The phosphors exhibit rod shape morphology with a uniform Eu(2+) distribution. Under n-UV excitation the emission spectra shift from 477 to 497 nm with an increase of Eu(2+) concentration. The concentration quenching mechanism of Eu(2+) emission was dominated by the dipole-dipole interaction. The thermal stability is comparable to that of the commercial Ba2SiO4:Eu(2+) phosphor. The phosphor also exhibits high current saturation and high resistance under low voltage electron bombardment. All the results indicate that the SrSiAl2O3N2:Eu(2+) phosphors can be considered as candidates for application in both white LEDs and FEDs.

The promising green oxynitride phosphor, Ba3-xMgxSi6O12N2:Eu(2+) was synthesized by the solid-state reaction method. The effect of Mg(2+) doping on the structure and photoluminescence (PL) properties of Ba3Si6O12N2:Eu(2+) was investigated systematically. The results reveal that the phosphor retains the single phase of Ba3Si6O12N2, with the lattice expanding upon increasing the Mg(2+) concentration, in an appropriate range. This suggests that a large portion of Mg(2+) enters into the interstitial sites of the crystal lattice. At a certain concentration, Mg(2+) doping can greatly enhance the absorption and PL intensity and decrease the full widths at half maximum (FWHM) of Ba3Si6O12N2:Eu(2+) phosphors. The green phosphor Ba2.87Eu0.1Mg0.03Si6O12N2 exhibited a small thermal quenching, which remained 82% of the initial emission intensity when measured at 150 °C. The quantum efficiency measured at 400 nm excitation was 38.5%. All the results indicate that the solid solution Ba3-xMgxSi6O12N2:Eu(2+) can be a good candidate for phosphors applicable in n-UV LEDs for solid-state lighting.