Negative Thermal Quenching of Photoluminescence: An Evaluation from the Macroscopic Viewpoint.

Negative thermal quenching (NTQ) denotes that the integral emission spectral intensity of a given phosphor increases continuously with increasing temperature up to a certain elevated temperature. NTQ has been the subject of intensive investigations in recent years, and a large number of phosphors are reported to have exhibited NTQ. In this paper, a collection of results in the archival literature about NTQ of specific phosphors is discussed from a macroscopic viewpoint, focusing on the following three aspects: (1) Could the NTQ of a given phosphor be reproducible? (2) Could the associated data for a given phosphor exhibiting NTQ be in line with the law of the conservation of energy? (3) Could the NTQ of a given phosphor be demonstrated in a prototype WLED device? By analyzing typical cases based on common sense, we hope to increase awareness of the issues with papers reporting the NTQ of specific phosphors based on spectral intensity, along with the importance of maintaining stable and consistent measurement conditions in temperature-dependent spectral intensity measurement, which is a prerequisite for the validity of the measurement results.

Comment on "Tunable thermal quenching properties of Na3Sc2(PO4)3:Eu2+ phosphors tailored by phase transformation details" by Z. Liu et al., Dalton Trans., 2020, 49, 3615.

Liu et al. (Dalton Trans., 2020, 49, 3615-3621) reported that emission of the Na3Sc2(PO4)3:Eu2+ phosphor showed tunable thermal quenching properties which were ascribed to the thermal event associated with polymorphic phase transformations. In this comment, I argue that the abnormal negative thermal quenching of the Na3Sc2(PO4)3:Eu2+ phosphor could be a pitfall caused by a diminishment in the optical path lengths of the spectrofluorometer originating from a continuous increase in the volume of the phosphor due to lattice thermal expansion and phase transformation at elevated temperatures.

Porous Graphene-Confined Fe-K as Highly Efficient Catalyst for CO2 Direct Hydrogenation to Light Olefins.

We devised iron-based catalysts with honeycomb-structured graphene (HSG) as the support and potassium as the promoter for CO2 direct hydrogenation to light olefins (CO2-FTO). Over the optimal FeK1.5/HSG catalyst, the iron time yield of light olefins amounted to 73 µmolCO2 gFe-1 s-1 with high selectivity of 59%. No obvious deactivation occurred within 120 h on stream. The excellent catalytic performance is attributed to the confinement effect of the porous HSG on the sintering of the active sites and the promotion effect of potassium on the activation of inert CO2 and the formation of iron carbide active for CO2-FTO.

ε-Iron carbide as a low-temperature Fischer-Tropsch synthesis catalyst.

ε-Iron carbide has been predicted to be promising for low-temperature Fischer-Tropsch synthesis (LTFTS) targeting liquid fuel production. However, directional carbidation of metallic iron to ε-iron carbide is challenging due to kinetic hindrance. Here we show how rapidly quenched skeletal iron featuring nanocrystalline dimensions, low coordination number and an expanded lattice may solve this problem. We find that the carbidation of rapidly quenched skeletal iron occurs readily in situ during LTFTS at 423-473 K, giving an ε-iron carbide-dominant catalyst that exhibits superior activity to literature iron and cobalt catalysts, and comparable to more expensive noble ruthenium catalyst, coupled with high selectivity to liquid fuels and robustness without the aid of electronic or structural promoters. This finding may permit the development of an advanced energy-efficient and clean fuel-oriented FTS process on the basis of a cost-effective iron catalyst.

Fe(x)O(y)@C spheres as an excellent catalyst for Fischer-Tropsch synthesis.

We demonstrate a one-pot hydrothermal cohydrolysis-carbonization process using glucose and iron nitrate as starting materials for the fabrication of carbonaceous spheres embedded with iron oxide nanoparticles. It is verified by TEM, (57)Fe Mossbauer, and Fe K-edge XAS that iron oxide nanoparticles are highly dispersed in the carbonaceous spheres, leading to a unique microstructure. A formation mechanism is also proposed. This route is also applicable to a range of other naturally occurring saccharides and metal nitrates. A catalytic study revealed the remarkable stability and selectivity of the reduced Fe(x)O(y)@C spheres in the Fischer-Tropsch synthesis, which clearly exemplifies the promising application of such materials.

Growth of porous single-crystal Cr2O3 in a 3-D mesopore system.

Single-crystal Cr2O3 with regular mesopores has been synthesized using mesoporous silica KIT-6 as a template and characterized by using XRD, HRTEM and nitrogen adsorption/desorption.

Solution route to single crystalline SnO platelets with tunable shapes.

Square and round single crystalline SnO platelets have been prepared in a solution-based chemical route aided with sonication at room temperature.

Highly efficient VOx/SBA-15 mesoporous catalysts for oxidative dehydrogenation of propane.

Highly dispersed vanadia species on SBA-15 mesoporous silica have been found to exhibit a highly efficient catalytic performance for the oxidative dehydrogenation (ODH) of propane to light olefins (propene + ethylene).