Juanhong Wang

Anomalous tunable visible to near infrared emission in the Mn2+-doped spinel MgGa2O4 and room-temperature upconversion in the Mn2+ and Yb3+-codoped spinel

In contrast to common visible emission, an anomalous near-infrared (NIR) emission band at 790 nm has been demonstrated in the spinel structure MgGa2O4:Mn2+ with heavy Mn2+ doping. Tunable single-band visible to visible-NIR and single-band NIR emission are easily realised upon tuning the doping concentration of Mn2+. Careful investigation of the crystal structure, fluorescence lifetime and excitation & emission spectra indicates that the NIR emission might be ascribed to the 6A1(6S)4T1(4G) → 6A1(6S)6A1(6S) transitions of Mn2+–Mn2+ dimers. When some Yb3+ ions are codoped into the spinel MgGa2O4:Mn2+, room temperature visible upconversion (UC) emission is realised upon excitation with a 976 nm laser diode. The temperature-dependent UC emission properties as well as the related UC mechanism have been investigated. Understanding the nature of the Mn2+ Stokes and UC emissions is the key to developing advanced photonic devices with improved properties and manufacturability for engineering applications.

In situ patterning of microgrooves via inkjet etching for a solution-processed OLED display

Inkjet-printing a solvent onto an insulating polymer layer is employed to in situ build microgrooves as bank structures in the application of a solution-processed OLED display. The inkjet-etching process not only eliminates photolithographys shadow mask and photo exposure, but is also capable of constructing bank structures on any functional layer. The orthogonal solubility between the CYtop polymer and the organic layer avoids any solvent erosion. A pixelated display is successfully fabricated by inkjet-printing a blue-emitting polymer onto inkjet-etched CYtop microgrooves with a pixel resolution of 140 lines per inch. Forming a bank structure in situ on any layer as needed offers more choices to design a new panel structure, device architecture, and deposition methods.

Room-temperature green to orange color-tunable upconversion luminescence from Yb3+/Mn2+ co-doped CaO

Room-temperature green to orange color-tunable upconversion (UC) luminescence has been achieved from Yb3+/Mn2+ co-doped CaO by adjusting the doping concentration of Mn2+ ions and the temperature of the samples upon 980 nm laser diode excitation. In this material system, the green UC emission band centered at 508 nm and the wavelength-tunable orange UC emission band from 560 to 725 nm are realized at 980 nm excitation, which originate from the cooperative luminescence of Yb3+ pairs and the |2F7/2, 4T1(4G)〉 → |2F7/2, 6A1(S)〉 transition of exchange-coupled Yb3+–Mn2+ dimers, respectively. The characteristic Stokes and UC emission properties, UC luminescence decay behaviors, temperature-dependent UC emission properties, as well as the involved UC mechanism of CaO:Yb3+,Mn2+ are investigated and discussed in detail. This study offers a new method to design novel UC materials for lighting and display applications instead of using conventionally investigated lanthanide (Ln3+) ions, such as Er3+, Tm3+ and Ho3+.

All‐Solution‐Processed Pure Formamidinium‐Based Perovskite Light‐Emitting Diodes

All-solution-processed pure formamidinium-based perovskite light-emitting diodes (PeLEDs) with record performance are successfully realized. It is found that the FAPbBr3 device is hole dominant. To achieve charge carrier balance, on the anode side, PEDOT:PSS 8000 is employed as the hole injection layer, replacing PEDOT:PSS 4083 to suppress the hole current. On the cathode side, the solution-processed ZnO nanoparticle (NP) is used as the electron injection layer in regular PeLEDs to improve the electron current. With the smallest ZnO NPs (2.9 nm) as electron injection layer (EIL), the solution-processed PeLED exhibits a highest forward viewing power efficiency of 22.3 lm W-1 , a peak current efficiency of 21.3 cd A-1 , and an external quantum efficiency of 4.66%. The maximum brightness reaches a record 1.09 × 105 cd m-2 . A record lifetime T50 of 436 s is achieved at the initial brightness of 10 000 cd m-2 . Not only do PEDOT:PSS 8000 HIL and ZnO NPs EIL modulate the injected charge carriers to reach charge balance, but also they prevent the exciton quenching at the interface between the charge injection layer and the light emission layer. The subbandgap turn-on voltage is attributed to Auger-assisted energy up-conversion process.