Zircon-type tetragonal LaVO4 phase is a suitable host for luminescent lanthanide ions but exhibits poor stability and transforms to monazite-type monoclinic phase at elevated temperatures and pressures. Here, we have studied the effect of partial substitution of La3+ with Eu3+ ions on the phase stability of tetragonal LaVO4 using the temperature and pressure induced phase transformation characteristics. Experimentally measured activation energy required for the initiation of phase transformation is found to increase with increasing europium content and suggests dopant induced stabilization of the tetragonal phase. The critical pressure (P c) and critical temperature (T c) required for tetragonal to monoclinic phase transition increase with increasing Eu3+ ions concentration, values being T c = 300, 500, and 600 °C and P c = 2, 4, and 6.5 GPa for compositions x = 0, 0.025, and 0.05, respectively. The simulations based on density functional theory (DFT) support the P c data, and the decrease in the formation energy of tetragonal La1–x Eu x VO4 (x = 0.0625–0.375) vis-à-vis monoclinic phase suggests improvement in its stability with increasing doping concentration. Further, the doped Eu3+ ions act as an optical probe and the observed variation in their luminescent characteristics is related to the structural transformation occurring due to pressure and heat treatment.

Reduction in the cost of renewable electricity has enhanced the viability of electrochemical CO2 reduction reaction (CO2RR) to chemicals. Ethylene is an economically desired product, and Cu is the only...

We explore the effect of sulfur doping in Co 3 V 2 O 8 on the electrochemical performance of supercapacitors in terms of enhanced lattice spacing, electrochemical surface area (ECSA), electronic conductivity, and density of states. The sulfur-doped Co 3 V 2 O 8 (S-Co 3 V 2 O 8 ) nanosheets were grown in situ as a binderfree synthesis on nickel foam by the hydrothermal method. The electrochemical performance was analyzed in an aqueous alkaline electrolyte where the S-Co 3 V 2 O 8 electrode exhibited a specific capacity of 410 mAh/g at 2 A/g with enhanced rate capability and capacity retention of 94.2% at 5 A/g specific currents after 4000 cycles, whereas the undoped Co 3 V 2 O 8 electrode exhibited a specific capacity of 337.8 mAh/g at 2 A/g. The high capacity of S-Co 3 V 2 O 8 is attributed to the enhanced ECSA (by ∼45%) and improved electrical conductivity (by ∼22%) upon doping with sulfur. Furthermore, these results corroborated with density functional theory results. The calculations suggest an increase in lattice parameters and the introduction of additional density of states near the valence-band edge due to the doping of sulfur, resulting in a decrease in charge-transfer resistance. An asymmetric supercapacitor was fabricated, using S-Co 3 V 2 O 8 nanosheets as the cathode and activated carbon as the anode, which shows a high specific capacity (or capacitance) value of 485 mAh/g, an energy density of 36.4 W h/kg, and a power density of 740 W/kg at 2 A/g with 98.4% specific capacity retention after 4000 consecutive charge−discharge cycles. Furthermore, the analysis was extended in a nonaqueous medium for Li-ion storage where S-Co 3 V 2 O 8 exhibits a specific capacity of 994 mA h/g and a specific energy density of 828 W h/kg at 1 A/g making it a promising candidate for future high-energy storage systems. The concept of doping is extended to other chalcogenide (e.g., selenium) doping (Se-Co 3 V 2 O 8 ), which also shows improved device performance and makes this a versatile approach for high-performance devices.

Incorporation of suitable lanthanide (Ln 3+ ) ions into semiconducting WO 3 can be useful to produce host-sensitized luminescence for solid-state lighting applications. Codoping of another Ln 3+ ion can assist in transferring energy from the host to the activator Ln 3+ ion to produce bright luminescence depending upon the electronic structure of the doped system. As a case study, Eu 3+ and Tb 3+ ion−doped WO 3 phosphors (WO 3 :Tb 3+x Eu 3+ y , x = 0−0.05 and y = 0−0.20) have been prepared over a wide range of doping concentrations to investigate the role of the Tb 3+ ion as a sensitizer and realize host-sensitized emission from Eu 3+ ions. The steady-state and time-resolved photoluminescence (TRPL) data for WO 3 :Tb 3+x Eu 3+ y (x = 0−0.05 and y = 0−0.10) samples confirm that Tb 3+ ions assist in excitation of Eu 3+ ions via sequential energy transfers from the host to Tb 3+ ions followed by Tb 3+ to Eu 3+ ions. The energy transfer process is controlled by optimizing their doping concentrations, and a single-phase white-light-emitting phosphor with a composition WO 3 :Tb 3+ 0.05 Eu 3+ 0.0005 has been developed. The electronic band structures and projected density of state plots for the WO 3 :Tb 3+ 0.03125 Eu 3+ 00.03125 system obtained using density functional theory (DFT)-based simulations confirm the formation of impurity states due to Eu 3+ and Tb 3+ ions within the forbidden gap of WO 3 . Based on the TRPL and DFT data, it is confirmed that the Tb 3+ ions act as a bridge between the conduction band edge of WO 3 and excited states of Eu 3+ ions to transfer energy and facilitate characteristic emission from europium species.

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