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Fluorescence latent fingerprinting (LFP) imaging is a convenient and frequently used in situ detection technique. In recent years, various types of phosphors have been widely used for LFP imaging. However, traditional phosphor powders are suffering from a formidable challenge to design effective fluorescent LFP powders with low background interference and high detection sensitivity. In this work, we have synthesized Zn2GeO4:Mn,Li,K (ZGO:Mn,Li,K) nanophosphors with the high persistent luminescence (PersL) brightness and long duration using hydrothermal method by optimizing synthesis conditions. The ZGO:Mn,Li,K phosphors, with a perceptible green PersL, have been successfully used for developing LFPs on non-fluorescent substrate, fluorescent substrate, and PersL substrate without special equipment. Besides the level 1 and level 2 details, the other details of LFPs even exceeding level 3 details including the ridge width and boundary streamline of LFPs and the sweat pore feature are distinguishable. These findings show that the ZGO:Mn,Li,K phosphors, with multimode luminescence and high detection sensitivity, will promise a more sophisticated luminescent label for LFP detection on various substrates. [ABSTRACT FROM AUTHOR]

Zn2GeO4 microrods obtained by thermal evaporation of a compacted powder mixture of ZnO and Ge exhibit quite intense UV luminescence at low temperatures. Herein, the luminescence properties of Zn2GeO4 microrods are studied for 2:1 and 1:1 ZnO:Ge ratio in the precursor mixture. In both cases, Zn2GeO4 microrods of high crystal quality produce a 355 nm emission under aforementioned bandgap excitation conditions at low temperatures. However, this emission vanishes at room temperature (RT) in the 1:1 samples while it is kept in the 2:1 ones. Herein this work, the thermal quenching of the UV luminescence is studied by means of steady and time‐resolved photoluminescence techniques from 4 K up to RT for both Zn2GeO4 microrods. The analysis of the results leads us to conclude that although the luminescence mechanisms are the same in both cases, a higher decay rate is observed in the 1:1 in both intensity and lifetime, which explain the observed thermal quenching at RT. [ABSTRACT FROM AUTHOR]

Achieving efficient and stable ultraviolet emission is a challenging goal in optoelectronic devices. Herein, we investigate the UV luminescence of zinc germanate Zn 2 GeO 4 microwires by means of photoluminescence measurements as a function of temperature and excitation conditions. The emitted UV light is composed of two bands (a broad one and a narrow one) associated with the native defects structure. In addition, with the aid of density functional theory (DFT) calculations, the energy positions of the electronic levels related to native defects in Zn 2 GeO 4 have been calculated. In particular, our results support that zinc interstitials are the responsible for the narrow UV band, which is, in turn, split into two components with different temperature dependence behaviour. The origin of the two components is explained on the basis of the particular location of Zn i in the lattice and agrees with DFT calculations. Furthermore, a kinetic luminescence model is proposed to ascertain the temperature evolution of this UV emission. These results pave the way to exploit defect engineering in achieving functional optoelectronic devices to operate in the UV region. [ABSTRACT FROM AUTHOR]

Novel transparent semiconducting oxides have emerged as key materials for a variety of optoelectronic applications due to their ultra-wide band gap. Owing to the critical role of native defects and impurities in the optoelectronical properties, investigation in detail of the electronic structure of these oxides has become a challenge, being luminescence technique a powerful way to gain insight into the electronic levels. Here, the photoluminescence temperature dependence of Li doped Zn 2 GeO 4 microrods is analysed and discussed in the framework of the electronic levels structure related to native defects and Li impurities. Unlike the undoped material, the blue emission (2.8 eV) of Li-doped germanate exhibits a negative thermal quenching as its photoluminescence intensity increases with increasing temperature. The mechanisms underlying this anomalous behaviour are discussed with the aid of X-ray photoemission spectroscopy and first principles calculations. This study has helped us to understand the role of Li in the electronic structure and optical reponse of Zn 2 GeO 4. Our results highlight the versatility of Zn 2 GeO 4 luminescence through Li doping, which could be exploited in optoelectronic devices with bespoke properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Zinc germanate doped with Mn 2+ (Zn 2 GeO 4 :Mn 2+ ) is known to be a persistent luminescence green phosphor with potential applications in biosensing and bioimaging. Such applications demand nanoparticulated phosphors with a uniform shape and size, good dispersibility in aqueous media, high chemical stability, and surface-functionalization. These characteristics could be major bottlenecks and hence limit their practical applications. This work describes a one-pot, microwave-assisted hydrothermal method to synthesize highly uniform Zn 2 GeO 4 :Mn 2+ nanoparticles (NPs) using polyacrylic acid (PAA) as an additive. A thorough characterization of the NPs showed that the PAA molecules were essential to realizing uniform NPs as they were responsible for the ordered aggregation of their building blocks. In addition, PAA remained attached to the NPs surface, which conferred high colloidal stability to the NPs through electrostatic and steric interactions, and provided carboxylate groups that can act as anchor sites for the eventual conjugation of biomolecules to the surface. In addition, it was demonstrated that the as-synthesized NPs were chemically stable for, at least, 1 week in phosphate buffer saline (pH range = 6.0-7.4). The luminescence properties of Zn 2 GeO 4 NPs doped with different contents of Mn 2+ (0.25-3.00 mol %) were evaluated to find the optimum doping level for the highest photoluminescence (2.50% Mn) and the longest persistent luminescence (0.50% Mn). The NPs with the best persistent luminescence properties were photostable for at least 1 week. Finally, taking advantage of such properties and the presence of surface carboxylate groups, the Zn 2 GeO 4 :0.50%Mn 2+ sample was successfully used to develop a persistent luminescence-based sandwich immunoassay for the autofluorescence-free detection of interleukin-6 in undiluted human serum and undiluted human plasma samples. This study demonstrates that our persistent Mn-doped Zn 2 GeO 4 nanophosphors are ideal candidates for biosensing applications.

Zinc germanate (Zn 2 GeO 4 ) microrods have been grown by a catalyst free thermal evaporation-deposition method. The microrods, with lengths of up to hundreds of microns have hexagonal cross section and faceted tips with morphologies in agreement with the rombohedral crystal structure of the germanate. Photoluminescence (PL) of the structures shows a broad band centered at about 2.4 eV, which is found by Gaussian deconvolution to consist of three components. A luminescence band at higher energies, centered at about 3.45 eV, is revealed by excitation with 20 kV electrons in the scanning electron microscope (SEM) or by PL under high excitation conditions. Resonance peaks observed in the luminescence spectra have been interpreted by the formation of Fabry–Perot modes in the hexagonal cross section of the rods. The waveguiding behavior of the rods has been assessed by excitation with a 325 nm laser and by detection of the excited luminescence emission transmitted along the rod. Micro Raman spectra of the rods show four bands in the range 740 cm −1 –820 cm −1 , with the most intense one peaked at 801 cm −1 . Comparison with Raman spectra of GeO 2 and of other germanates suggests that this set of bands, characteristic of Zn 2 GeO 4 is related to vibrations of Ge–O bonds. [ABSTRACT FROM AUTHOR]

Abstract: Amorphous and crystalline Zn2GeO4 nanoparticles were prepared and characterized as anode materials for Li-ion batteries. A higher reversible specific capacity of 1250mAh/g after 500 cycles and excellent rate capability were obtained for amorphous Zn2GeO4 nanoparticles, compared to that of crystalline Zn2GeO4 nanoparticles. Small particle size, amorphous phase and incorporation of zinc and oxygen contribute synergetically to the improved performance by effectively mitigating the huge volume variations during lithiation and delithiation process. [Copyright &y& Elsevier]

Abstract: Thin films of zinc germanate doped with manganese (Zn2GeO4:Mn) were fabricated by radio frequency magnetron sputtering, and their structural characteristics and luminescent properties were studied. The Zn2GeO4:Mn films exhibited a pronounced absorption edge at around 271nm and a high optical transparency in the visible wavelength region with a peak transmittance of 0.927 at 691nm. While the as-deposited Zn2GeO4:Mn films had an amorphous structure, the annealed films possessed a rhombohedral polycrystalline structure with a random crystallographic orientation of grains. The broad-band photoluminescence (PL) emission was observed from the annealed Zn2GeO4:Mn films. The PL emission spectrum showed a peak maximum at around 537nm in the green range, which was accounted for by the intrashell transition of 3d 5 orbital electrons from the 4T1 lowest excitation state to the 6A1 ground state in the divalent manganese ions. Two discrete peaks were observed in the PL excitation spectrum at 256 and 296nm, which are considered to be associated with the band-to-band absorption of the host and the sub-band absorption from defect states, respectively. The green cathodoluminescence (CL) emission was obtained from the annealed Zn2GeO4:Mn films with a peak centered at around 534nm, analogous to the PL emission spectrum. [ABSTRACT FROM AUTHOR]

• Zn 2 GeO 4 nanocrystals (NCs) were synthetized by a precipitation method. • The NCs show UV and visible emissions at low temperature related to native defects. • The optical bandgap of the NCs was estimated. • The activation energies of the non-radiative channels in the NCs were calculated. • The NCs display a cold-white emission at room temperature. Energy flat band model in Zn 2 GeO 4 NCs due to native defects and photograph of compacted Zn 2 GeO 4 NCs under illumination with a UV laser. [Display omitted] Broad emission bands in semiconducting oxides due to native defects could readily be an efficient source of white light if they are adjusted properly. In this work, Zn 2 GeO 4 nanoparticles of 10 and 16 nm sizes, obtained by a precipitation method, are presented as potential white light emitter. Temperature dependence measurements have been performed to discuss the Zn 2 GeO 4 luminescence, which consist of emission bands in the ultraviolet, blue and green regions. The analysis of these results provided some clues about the interplay between defect-related centres and the surface states in nanocrystalline Zn 2 GeO 4. Finally, a highly efficient cold-white emission at room temperature has been achieved from this nanomaterial. [ABSTRACT FROM AUTHOR]

• The role of surface conditions on the UV emission of Zn 2 GeO 4 has been investigated. • A 4.40 eV (280 nm) emission has been observed in SnO 2 coated Zn 2 GeO 4 nanowires. • Zn 2 GeO 4 surface passivation allows the activation of shallow levels. Herein, we report the influence of the surface conditions on the cathodoluminescence (CL) emissions from Zn 2 GeO 4 nanowires and Zn 2 GeO 4 /SnO 2 heterostructures obtained by thermal evaporation technique. A Zn 2 GeO 4 nanowire surrounded by a discontinuous shell of SnO 2 crystals composed the Zn 2 GeO 4 /SnO 2 heterostructures. Local CL measurements at different acceleration voltages allow monitoring the emission bands originated at the interface region, showing an additional deep-ultraviolet (UV) emission at 4.40 eV, which has not been previously reported. CL spectra from SnO 2 coated Zn 2 GeO 4 nanowires also show this deep-UV emission. The results would confirm the presence of a shallow energy level close to the conduction band, which becomes active by passivation of Zn 2 GeO 4 nanowires surface by the SnO 2 coating. [ABSTRACT FROM AUTHOR]

• Low-temperature hydrothermal route was used for synthesis of highly crystalline Zn 2 GeO 4 nanorods. • A shrinkage in the optical band gap (3.96 eV) was observed. • High dielectric constant of ~772 and phase transition was observed around 400 °C. • Activation energy of ~0.33 and 1.34 eV were observed. This work reports the high temperature anomalous phase transition with high dielectric constant and low band gap in pure zinc germanate (Zn 2 GeO 4) nanorods. Crystal structure of Zn 2 GeO 4 nanorods were analyzed by X-ray powder diffraction and Raman studies. Electron microscopy reveals that nanorods have average diameter and length of 30 nm and 100 nm, respectively. UV–ViS study indicates low band gap of 3.96 eV. The observed dielectric constant is 40 times higher than bulk Zn 2 GeO 4. High dielectric constant of ~772 and phase transition was observed around 400 °C. In the low and high temperature range, activation energy were ~0.33 and 1.34 eV. High dielectric constant and shrinkage in bang gap with temperature phase transition of Zn 2 GeO 4 nanorods makes it the potential candidate for nano-optoelectronic and nanodevices applications in near future. [ABSTRACT FROM AUTHOR]

The optical properties of zinc germanate microrods are investigated and correlated with vibrational modes of the crystalline structure. The samples are grown by a thermal evaporation method using ZnO and Ge as precursors. Polarized Raman spectroscopy and polarized micro‐photoluminescence techniques are applied in order to shed some light into the origin of the luminescence in Zn2GeO4. Oxygen defects are usually responsible for light emission in most of semiconducting oxides. Here, the authors report two luminescence bands at room temperature, a broad green one at about 2.4 eV and an ultraviolet one at 3.2 eV, which are of composed nature. In addition, the authors observe changes in the Raman and PL spectra recorded with polarizers oriented parallel or orthogonal to the microrod axis. The evolution of the luminescence bands in Zn2GeO4 and their correlation with the observed Raman modes (O‐Ge‐O and Ge‐O‐Zn vibration modes) are discussed in the framework of oxygen defects in the Zn2GeO4 structure. Vibrational modes and luminescence bands of Zn2GeO4 microwires are investigated. The correlation between vibrational modes in polarized Raman measurements and luminescence bands are explored. Besides the orientation of the wires, some insights into the oxygen defects that are involved in the luminescence bands are discussed. [ABSTRACT FROM AUTHOR]