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Study on the growth of a Li+-doped CsCu2I3 crystal for dual gamma-ray and neutron detection.

Derivatization of 2D materials for bioapplications is at the forefront of nanomaterials research nowadays. Facile synthesis of the biografted 2D derivatives and insight into the conformation of the conjugated biomolecules are two pillars, promoting advances in the field of biosensing, drug delivery and regeneration techniques. This work is devoted to the synthesis and conjugation of carboxylated graphene by aptamers followed by theoretical analysis of their conformation in the immobilized state. Employing the developed method, the hole-matrixed graphene with up to 11.1 at.% reactive carboxyl groups was synthesized and thoroughly examined via core-level spectroscopy and time-resolved methods. The mechanism of the performed carboxylation with conversion of graphene oxide into carboxylated graphene is proposed, unveiling commonly disregarded impact of ether-like components to the fingerprints of the carboxyl groups. We show successful covalent immobilization of the AO-01 aptamer against Hepatitis B protein on the synthesized C-xy graphene and for the first time reveal its conformation both in free and immobilized forms via a combination of density functional theory (DFT) calculations and molecular dynamic (MD) modeling. Taken together, these results advance the application of graphene derivatives grafted with the biomolecules in the field of biosensing.

Study on the growth and scintillation mechanism of Li+-doped Cs3Cu2I5 crystal with an excellent FOM value for dual gamma-ray and neutron detection applications.

Low-dimensional copper-based halide perovskite single crystals are considered excellent scintillators for indirect X-ray detection, but their potential in direct X-ray detection has not been investigated. Herein, high-quality pure Cs3Cu2I5 and Li-doped Cs3Cu2I5:Li single crystals are grown by the Bridgman method. The Li+ dopant enhances the photoelectric properties of the Cs3Cu2I5 single crystal by extending the carrier life time, improving the carrier mobility from 6.49 to 9.52 cm2V-1s-1, and increasing the mobility-lifetime (μτ) product from 1.4×10-4 to 2.9×10-4 cm2V–1. The sensitive direct X-ray detector with a vertical device configuration of Au/Cs3Cu2I5:Li single crystal/PCBM/Au is fabricated and demonstrated to have a high sensitivity of 831.1 µC Gyair -1 cm-2 and low detection limit of 34.8 nGyair s-1. Furthermore, the detector shows fast response, negligible baseline current drift and excellent stability upon X-ray illumination.

Self-activated phosphors without any luminescent dopants, usually display excellent optical properties, such as high oscillator strength, large Stokes shift, and strong luminescence efficiency, and thus have been widely investigated by researchers for several decades. However, their recent advancements in scintillators, white-light illumination, displays and optical sensors compel us to urgently understand the basic principles and significant technological relevance of this worthy family of materials. Herein, we review the structures, photoluminescence principles, and applications of state-of-the-art self-activated phosphors, such as borate, gallate, niobate, phosphate, titanate, vanadate, tungstate, nitrides, oxyfluoride, perovskite, metal halides, and carbon dots. The photoluminescence principles of self-activated phosphors are mainly summarized as transitions between energy levels of rare-earth and transition metal ions, charge transfer transitions of some oxide compounds, and luminescence in all-inorganic semiconductors. The different self-activated phosphors exhibit various structures and site-dependent spectra. Additionally, we discuss the application prospect and main challenges of self-activated phosphors.

CaB

Luminescence properties of sodalite Zn4B6O13:Mn2+ are investigated by optical and laser excitation spectroscopy in the temperature range 10 – 300 K. The samples of Zn4B6O13:Mn2+ are prepared in the carbon reducing atmosphere. The green emission at 540 nm are observed in Zn4B6O13:Mn2+ for various Mn2+ concentration. Optimum Mn2+ concentration and critical distances between Mn2+ ions in Zn4B6O13 are obtained by the luminescence intensity as functions of Mn2+ concentration. The decays of Mn2+ emission depend strongly on Mn2+ concentration due to the energy transfer and energy diffusion in Zn4B6O13:Mn2+. The fine structures consisting of the intense zero phonon line (ZPL) and weak vibrational sidebands are observed at low temperature. The relevant mechanism of excitation bands, ZPL, vibrational sidebands and the bandwidth as functions of temperature are interpreted in detail by energy level diagram of the 3d5 transition metal ions and configuration coordinated diagram. The high thermal stability of the Zn4B6O13:Mn2+ phosphor are observed in the temperature range 10–300 K.

The Y2WO6:Yb3+/Er3+ crystals were synthesized by the hydrothermal method. The needle-shaped morphology is controllably formed and a number of crystals aggregate as spheres by adding the surfactant of sodium dodecylbenzenesulfonate (SDBS) into the reaction system. The crystal structure, morphology and upconversion luminescence properties of the Y2WO6:Yb3+/Er3+ crystals are conducted on the basis of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), FTIR and emission spectra. The different emission intensity ratio of the red and green bands is observed for the Y2WO6:Yb3+/Er3+ precursors under different heat treatments. The different intensity ratio are illustrated according to the upconversion mechanism.

Luminescence properties of impurity-trapped excitons (ITEs) in LiBaF3:Eu2+ crystals are investigated by optical and time-resolved laser-excitation spectroscopy. The three excited states of 4f65d, 4f7(6P7/2) and ITE are identified in the excitation and emission spectra. The intensity of ITEs’ emission increases unexpectedly with increasing temperature and excitation energy. The initial intensity of the ITE emission just after pulsed-laser excitation increases continuously with temperature in the temperature range 7–600 K. The results are discussed in relation to radiative and nonradiative rates and excitonic processes in this system. The theoretical model that includes the ITE, 4f7(6P7/2) and 4f6(7FJ)5d(eg) states is developed to describe and support the experimental observations.

Eu3+-doped Gd10(1-x)Eu10xV2O20 (x = 0 – 1) phosphors were synthesized via the sol-gel process. The formation of a single phase compound was verified through the X-ray diffraction studies. Luminescence properties of Gd10V2O20:Eu3+ are investigated by optical and laser excitation spectroscopy. The emission and excitation spectra, luminescence decays were measured in the temperature region 7–300 K. The strong emission due to the vanadate group of Gd10V2O20:Eu3+ is observed at low temperature. The charge transfer transition of Eu3+ depends strongly on the Eu3+-concentration in Gd10V2O20:Eu3+. The emission intensity as a function of Eu3+ concentration under excitation of charge transfer band is inconsistent with that of the 4f7 states (the 5L6 state) of Eu3+. The energy transfer occurs between two Eu3+ ions at low Eu3+ concentration (

Ba5Al3F19:Eu2+ blue-emitting phosphors were synthesized by the solid state reaction in a reductive atmosphere. The crystal structure of Ba5Al3F19:Eu2+ phosphors were characterized by using the X-ray powder diffraction (XRD) measurement. The luminescence properties are investigated systematically based on the crystal structure. Emission and excitation spectra of the Ba5Al3F19:Eu2+ phosphor along with the decay curves were characterized. Under the excitation of UV light, the phosphor exhibits a broad band emission around 410 nm ascribed to the allowed 4f65d→4f7(8S7/2) transition, together with a sharp line at 360 nm corresponding to the forbidden 4f7(6P7/2)→4f7(8S7/2) transition of the Eu2+ ions. The temperature dependent emission spectra and decay curves were measured to investigate the origins of the emission and the thermal stabilities of the as-prepared phosphors. The as-prepared Ba5Al3F19:Eu2+ phosphors display interesting and stable luminescence properties, which can act as promising blue-emitting phosphor candidates.

A Mn4+ doped Na2WO2F4 phosphor was synthesized through a two-step wet chemical method. The relationship between crystal structure and luminescence properties is discussed and unusual strong intense zero phonon lines (ZPLs) have been found in a distorted octahedral environment. The power dependent luminescence spectra exhibit the existence of down conversion luminescence intensity saturation under a high pumping power limit. The fluorescence intensity ratios of anti-Stokes bands to the ZPL and Stokes bands reveal an obvious temperature dependent relationship based on thermal de-population from the low states to the upper states of an intrinsic Mn4+ 2Eg → 4A2g transition. The temperature dependent emission intensity of Mn4+ is investigated by changing the excitation power, and an optical temperature sensitivity as high as 0.00658 K−1 is achieved at 193 K with the intensity ratio of anti-Stokes bands to the ZPL under 488 nm excitation by a Xenon lamp. This work presents a new method to realize optical thermometry at low temperature by controlling the intensity ratio of the anti-Stokes bands to the ZPL.

Eu 3+ -doped NaGd(WO 4 ) 2 nanophosphors were synthesized via a facile one-step hydrothermal method without any surfactants or a further heat treatment. X-ray powder diffraction (XRD), scanning electron microscope (SEM), fourier transform infrared spectroscopy (FT-IR), the photoluminescence (PL) excitation and emission spectra, and decay curves were used to characterize NaGd(WO 4 ) 2 :Eu 3+ phosphors. The results show that the Eu 3+ -concentration has little influence on the structure and morphology of the as-synthesized samples. However, pH value plays a vital role on the structure and morphology of NaGd(WO 4 ) 2 . The well-crystallized sheet-like NaGd(WO 4 ) 2 phosphors can be obtained only at pH = 5–7. On the basis of the time-dependent synthesis, a possible growth mechanism of sheet-like architectures is proposed. The luminescence properties of NaGd 1-x Eu x (WO 4 ) 2 (0 ≤ x ≤ 1) are investigated. It is found that the charge transfer band of Eu 3+ shifts to lower energy and broadens with increasing the Eu 3+ -concentration.

The inconsistent thermal quenching performance of manganese(II)-doped Cs3Cu2I5 microparticles is exploited in a highly sensitive noninvasive optical thermometer. The ratio of the emissions of Cu(II) and Mn(II) ions in the microparticles is highly temperature dependent in the range from 298 to 498 K. The best absolute and relative sensitivities are 0.547 K−1 and 0.525% K−1, respectively. The emission spectrum, under 300-nm photoexcitation, has emission peaks at 448 and 556 nm. This is the result of energy transfer between the Cu(II) and Mn(II) ions whose efficiency can reach up to 57% when the Mn(II) ion concentration is 2 mol%. The emission color of the microparticles changes from cyan to green when increasing the temperature from 298 to 498 K.

The surface ligands of the quantum dots (QDs) play an important role in the performance of quantum dots based optoelectronic devices. However, the native surface ligands of long-chain non-polar aliphatic compounds are hydrophobic, which limits the application of QDs for further device fabrication. Here, we reported a simple and fast method for cap exchange of CdSe/CdS/ZnS quantum dots using thiol functional ligands. We can successfully transfer QDs from non-polar to polar solvents by utilizing this facile method without significant fluorescence quenching.

Two-dimensional (2D) halide perovskite materials have attracted great attention because of their impressive optoelectronic properties in light-emitting diodes (LED), sensors and solar cells, etc. Recently, it has been shown that the low dimensional perovskites with direct white light emission may act as the single component phosphors in next generation white-LEDs. Here, we demonstrate the temperature dependent photoluminescence (PL) properties of white light 2D perovskites by laser excitation. Spectroscopic measurements suggest that the white light spectrum consist of free exciton (FE) and self-trapped exciton (STE). The relative intensities between the FE and STE are temperature dependent, and the energy tunneling effect is dominated at low temperature while the thermal quenching is responsible for the higher temperature region. Our results give the physical insight of the energy transfer and thermal behaviours of the excitons in 2D perovskites.