A series of novel orange-red emitting tantalate phosphors, Sr 2 Ta 2 O 7 :xEu 3+ (0.01 ≤ × ≤ 0.13) were successfully prepared through the solid-state method at high temperature. Under the excitation of 464 nm, Sr 2 Ta 2 O 7 :Eu 3+ emits orange-red light at 597 nm. The PL spectra of Sr 2 Ta 2 O 7 :Eu 3+ phosphors are ascribed to the 5 D 0 → 7 F J ( J = 0, 1, 2, 3 and 4) transitions of Eu 3+ ions. The optimal doping concentration of Eu 3+ ions was 9 mol%. The optical bandgap of the host was calculated by ultraviolet-visible diffuse reflection spectra (DRS) with a value of 4.73 eV. The emission intensity of phosphors at 423 K still maintains 92% of that at room temperature, which means the material has excellent thermal stability. The chromaticity coordinates of the Sr 2 Ta 2 O 7 :Eu 3+ located in the orange-red region (0.6403, 0.3585). Various results show that Eu 3+ -doped Sr 2 Ta 2 O 7 phosphors have great potential in the field of phosphor conversion white light-emitting diodes (pc-WLEDs).
Weixuan Zeng,Sheng Cao,Lulu Qiao,Anquan Zhu,Quanyin Ma,Xiewen Xu,Yi Chen,Jun Pan
In the present study, we report a one-step hydrothermal synthesis of visible-light response Cr-doped Sr2Ta2O7 nanosheets for photocatalytic hydrogen generation. It is discovered that the Cr ion is successfully doped into the Sr2Ta2O7 nanosheet crystal lattice and uniformly distributed without changing the crystal structure and morphology of the Sr2Ta2O7 host. Compared to pristine Sr2Ta2O7, the as-prepared Cr-doped Sr2Ta2O7 photocatalysts show enhanced photocatalytic activity for hydrogen generation under visible-light irradiation. The spectroscopy and Mott–Schottky results reveal that proper Cr doping can narrow the band gap of Sr2Ta2O7 as well as facilitate the separation of photo-generated electrons and holes, thus enhancing the photocatalytic performance under visible-light irradiation. This work provides a simple approach to fabricate visible-light active tantalum-based oxide photocatalysts.
Visible light-driven photocatalytic hydrogen production has been deemed a potential means to solve the increasingly serious energy shortage problem. Herein, two dimensional (2D) Sr 2 Ta 2 O 7 /S-doped g-C 3 N 4 nanocomposites that applied in photocatalytic water reduction were fabricated through thermal condensation of thiourea with hydrothermal-prepared Sr 2 Ta 2 O 7 . The resulted Sr 2 Ta 2 O 7 /S-doped g-C 3 N 4 nanocomposite exhibited enhanced hydrogen evolution rate (11.36 μmol g −1 h −1 ) under visible light irradiation, which is about 3.5 times higher than that of pure S-doped g-C 3 N 4 . In light of the UV–vis diffuse reflectance spectroscopy, Mott-Schottky curve and photoluminescence spectra, the enhanced photocatalytic performance could be mainly attributed to the conduction band difference between Sr 2 Ta 2 O 7 and S-doped g-C 3 N 4 . In addition, transient photoluminescence spectra, electrochemical impedance spectra and photocurrent responses proved that the presence of Pt cocatalyst also plays an important role in facilitates the transport of photoexcited electron-hole pairs, subsequently promoting the photocatalytic performance.
In this paper, a novel afterglow phosphor based on praseodymium ion doped Sr 2 Ta 2 O 7 was synthesized successfully by solid-state reaction in the ambient atmosphere. The photoluminescence, afterglow, afterglow decay, and thermoluminescence (TL) properties were investigated in detail. The dependence of photoluminescence properties and long afterglow (LAG) performances on Pr 3+ contents were investigated systematically. The optimal concentrations of Pr 3+ ions for the best photoluminescence and LAG properties were experimentally to be 2 mol% and 0.5 mol%, respectively. Pr 3+ exhibits prominent red emission in most reports, which derives from the 1 D 2 → 3 H 4 transition. However, the predominant blue emission locating at ∼489 and ∼507 nm coming from 3 P 0,1 → 3 H 4 transitions were observed in praseodymium ion-doped Sr 2 Ta 2 O 7 . Based on TL measurements, the trapping and de-trapping processes of charge carriers between shallower and deep traps were illustrated. A model was proposed on the basis of experimental results to explain the mechanisms of photoluminescence and LAG.
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