Jingshan Hou

Ultrabroad Photoluminescence and Electroluminescence at New Wavelengths from Doped Organometal Halide Perovskites

Doping of semiconductors by introducing foreign atoms enables their widespread applications in microelectronics and optoelectronics. We show that this strategy can be applied to direct bandgap lead-halide perovskites, leading to the realization of ultrawide photoluminescence (PL) at new wavelengths enabled by doping bismuth (Bi) into lead-halide perovskites. Structural and photophysical characterization reveals that the PL stems from one class of Bi doping-induced optically active center, which is attributed to distorted [PbI6] units coupled with spatially localized bipolarons. Additionally, we find that compositional engineering of these semiconductors can be employed as an additional way to rationally tune the PL properties of doped perovskites. Finally, we accomplished the electroluminescence at cryogenic temperatures by using this system as an emissive layer, marking the first electrically driven devices using Bi-doped photonic materials. Our results suggest that low-cost, earth-abundant, solution-processable Bi-doped perovskite semiconductors could be promising candidate materials for developing optical sources operating at new wavelengths.

Unconventional Luminescent Centers in Metastable Phases Created by Topochemical Reduction Reactions

A low-temperature topochemical reduction strategy is used herein to prepare unconventional phosphors with luminescence covering the biological and/or telecommunications optical windows. This approach is demonstrated by using Bi(III)-doped Y2O3 (Y(2-x)Bi(x)O3) as a model system. Experimental results suggest that topochemical treatment of Y(2-x)Bi(x)O3 using CaH2 creates randomly distributed oxygen vacancies in the matrix, resulting in the change of the oxidation states of Bi to lower oxidation states. The change of the Bi coordination environments from the [BiO6] octahedra in Y(2-x)Bi(x)O3 to the oxygen-deficient [BiO(6-z)] polyhedra in reduced phases leads to a shift of the emission maximum from the visible to the near-infrared region. The generality of this approach was further demonstrated with other phosphors. Our findings suggest that this strategy can be used to explore Bi-doped or other classes of luminescent systems, thus opening up new avenues to develop novel optical materials.

Superbroad near-infrared photoluminescence covering the second biological window achieved by bismuth-doped oxygen-deficient gadolinium oxide

In this work, we demonstrated that bismuth-doped oxygen-deficient gadolinium oxides, produced through a low-temperature topochemical reduction strategy using CaH2 as a solid-state reducing agent, show superbroad near-infrared photoluminescence covering the second biological window. Structural analyses confirm that the topochemical reduction treatment of bismuth-doped gadolinium oxides creates oxygen vacancies in the gadolinium oxide matrix, which changes the coordination of Bi and makes it situate in a defective environment. Given the tantalizing superbroad near-infrared emission from the reduced phases, it is anticipated that this novel system may find applications for in vitro/in vivo near-infrared fluorescence imaging in the second biological window.

Ultrabroad near-infrared photoluminescence from bismuth doped CsPbI3: polaronic defects vs. bismuth active centers

Bismuth doped materials with near infrared (NIR) photoluminescence (PL) have recently attracted tremendous attention because of their great potential for photonic and optoelectronic devices that could find broad applications in modern optical telecommunications. However, the mechanistic studies of the NIR PL from these materials still significantly lag behind, which imposes substantial limitations in rationally discovering and designing new materials. In this contribution, we investigated the optical and structural properties of Bi doped CsPbI3 using a diverse range of experimental techniques. We proved that the observed ultrabroad NIR PL with lifetimes of tens of microseconds is not connected with a single-ion Bi active center. For the first time, we proposed a polaron model to rationally explain the observed PL from Bi doped CsPbI3. Finally, we demonstrate the first observation of NIR PL from nanowires among the Bi doped luminescent materials. The experimental results reported here not only deepen the understanding of NIR PL mechanisms in Bi doped materials, but also introduce a new family of solution-processed nanostructures operating in the NIR, which may stimulate further research in exploiting this technique to design a broad range of photonic and optoelectronic devices.

Air-stable and highly luminescent bismuth complex nanoparticles

We report, for the first time, the preparation of air-stable, solution-processed, luminescent Bi complex nanoparticles (NPs) through a one-pot wet chemical reaction method. Strong visible photoluminescence (PL) from these Bi complex NPs, with a quantum yield as high as 5.9%, can be achieved. Interestingly, the observed PL is distinctly different from other materials containing Bi. Based on detailed analyses, a multi-stage formation and growth process for the Bi complex NPs has been proposed, and the observed PL is attributed to the intrinsic electronic transition inherent to the whole NPs. This work not only provides a synthetic method for luminescent NPs with sizes larger than 2 nm, but also can contribute significantly to a better understanding of the photophysical behaviors of materials containing the Bi element.

Influence of the synthesis atmosphere on NIR fluorescence behavior of Ce/Er co-doped bismuth glass through valence state changes of cerium

This work investigates the near-infrared emission characteristics and energy transfer between erbium and cerium in bismuth glass by the reaction atmosphere process. The Er3+:1.5μm emission can be successfully enhanced by performing a reduction conversion of Ce4+→Ce3+ using a reducing atmosphere. The discrepancies of the energy structure between Ce3+ and Ce4+ result in a contrasting sensitizing effect on Er3+:1.5μm emission intensity and decay lifetime. The results show that a significant amount of Ce3+ is present in glasses prepared in a reducing atmosphere, whereas Ce4+ is the main species in an oxidizing atmosphere by means of absorption spectra and XPS curves. The reason for upconversion quenching is also discussed.

White-light-emitting from single-phased (Ca,Eu,Mn)9Al(PO4)7 phosphor with blue-white-yellow tunable luminescence properties for UV-based LEDs

ABSTRACT Single-phased white light emitting (Ca,Eu,Mn)9Al(PO4)7 phosphors were synthesized by conventional one-step reduction solid state reaction. The emission colors could be tuned from blue (0.170, 0.082) to white light (0.299, 0.316) and eventually to yellow (0.390, 0.400) through an efface energy transfer by controlling the dopant Eu2+/Mn2+ concentration. Energy transfer between the sensitizer Eu2+ and the activator Mn2+ has been studied and demonstrated to be a resonant type via a dipole-dipole interaction mechanism. Emissions from Eu2+ and Mn2+ in Ca9Al(PO4)7 exhibits excellent thermal stability and synchronicity. Finally, a white-LED with Ra = 79 was fabricated by using a 380 nm UV chip with single-phased (Ca0.965Eu0.005Mn0.03)Al(PO4)7 phosphor.