Terms Of Luminescence Research Articles

Genome assembly of Genji firefly (Nipponoluciola cruciata) reveals novel luciferase-like luminescent proteins without peroxisome targeting signal.

The Genji firefly, Nipponoluciola cruciata, is an aquatic firefly endemic to Japan, inhabiting a wide area of the Japanese archipelago. The luminescence of fireflies is a scientifically interesting phenomenon, and many studies have evaluated this species in Japan. In this study, we sequenced the whole genome of male N. cruciata and constructed a high-quality genome assembly of 662Mb with a BUSCO completeness of 99.1% in the genome mode. Using the detected set of 15,169 protein-coding genes, the genomic structures and genetic background of luminescence-related genes were also investigated. We found four new firefly luciferase-like genes in the genome. The highest bioluminescent activity was observed for LLa2, which originated from ancestral PDGY, a mitochondrial acyl-CoA synthetase. A thioesterase candidate, NcruACOT1, which is involved in d-luciferin biosynthesis, was expressed in the lantern. Two opsins were also detected and the absorption wavelength of the UV-type opsin candidate shifted from UV to blue. These findings provide an important resource for unravelling the adaptive evolution of fireflies in terms of luminescence and vision.

Effect of the synthesis route on luminescence dynamics and thermographic properties of Sm3+ doped Ba2Mg(PO4)2 phosphor

The present study investigates the impact of synthesis routes on the structure, optical, and thermographic properties of Ba2Mg(PO4)2:xSm3+ (x = 2 mol.%) phosphor. The two techniques used for the synthesis were combustion synthesis (CS) and solid-state reaction synthesis (SSR). X-ray diffraction analysis confirmed a pure monoclinic phase with space group P21/n in both SSR and CS synthesized samples. The average crystallite size was 41 ± 0.19 nm for SSR and 21 ± 0.02 nm for CS phosphors. Using Fourier transform infrared (FTIR) analysis, the vibrational behavior of both synthesized phosphor samples was analyzed. Both samples displayed a bright orange-red photoluminescence (PL) emission, attributed to the 4G5/2→6H7/2 transition when excited with 403 nm light at room temperature. However, the intensity of PL emission was higher in the CS-prepared sample. The UV-Vis absorption measurements indicated several bands in both samples. The CIE coordinates were calculated for both samples and they corresponded to the shade of orange-red emission of the Sm3+ ions. The study also included an investigation into the temperature-sensing characteristics of the synthesized phosphors, which was performed in the 323–673 K temperature range. The fluorescence intensity ratio (FIR) technique was used to study the non-contact temperature sensing for both samples, and the CS-prepared phosphors exhibited the maximum value of absolute sensitivity (0.00629 K−1) and relative sensitivity (0.26 % K−1) at temperature 673 K. Overall, the results indicate that the CS method provides better results in terms of luminescence and temperature sensing characteristics compared to the SSR method.

4 in 1: multifunctional europium-organic frameworks with luminescence sensing properties, white light emission, proton conductivity and reverse acetylene-carbon dioxide adsorption selectivity.

Lanthanide metal-organic frameworks (Ln-MOFs) combine the lanthanide luminescence characteristics and the advantages of porous materials, which can be used in various research fields by exploring their multifunctional properties. A three-dimensional water-stable and high-temperature resistant Eu-MOF [Eu(H2O)(HL)]·0.5MeCN·0.25H2O (H4L = 4-(3,5-dicarboxyphenoxy)isophthalic acid), demonstrating a high photoluminescence quantum yield, was synthesized and structurally characterized. In terms of luminescence, the Eu-MOF exhibits excellent selectivity and quenching sensing for Fe3+ (LOD = 4.32 μM) and ofloxacin, as well as color modulation with Tb3+ and La3+ to develop white LED components with high illumination efficiency (color rendering index, CRI = 90). On the other hand, narrow one-dimensional channels of the Eu-MOF decorated with COOH groups enable a rare reverse adsorption selectivity in a CO2/C2H2 gas mixture. In addition, the protonated carboxyl groups in the Eu-MOF provide an efficient conducting platform for proton transfer with a conductivity value of 8 × 10-4 S cm-1 at 50 °C and RH 100%.

Advancing X-ray Luminescence for Imaging, Biosensing, and Theragnostics.

ConspectusX-ray luminescence is an optical phenomenon in which chemical compounds known as scintillators can emit short-wavelength light upon the excitation of X-ray photons. Since X-rays exhibit well-recognized advantages of deep penetration toward tissues and a minimal autofluorescence background in biological samples, X-ray luminescence has been increasingly becoming a promising optical tool for tackling the challenges in the fields of imaging, biosensing, and theragnostics. In recent years, the emergence of nanocrystal scintillators have further expanded the application scenarios of X-ray luminescence, such as high-resolution X-ray imaging, autofluorescence-free detection of biomarkers, and noninvasive phototherapy in deep tissues. Meanwhile, X-ray luminescence holds great promise in breaking the depth dependency of deep-seated lesion treatment and achieving synergistic radiotherapy with phototherapy.In this Account, we provide an overview of recent advances in developing advanced X-ray luminescence for applications in imaging, biosensing, theragnostics, and optogenetics neuromodulation. We first introduce solution-processed lead halide all-inorganic perovskite nanocrystal scintillators that are able to convert X-ray photons to multicolor X-ray luminescence. We have developed a perovskite nanoscintillator-based X-ray detector for high-resolution X-ray imaging of the internal structure of electronic circuits and biological samples. We further advanced the development of flexible X-ray luminescence imaging using solution-processable lanthanide-doped nanoscintillators featuring long-lived X-ray luminescence to image three-dimensional irregularly shaped objects. We also outline the general principles of high-contrast in vivo X-ray luminescence imaging which combines nanoscintillators with functional biomolecules such as aptamers, peptides, and antibodies. High-quality X-ray luminescence nanoprobes were engineered to achieve the high-sensitivity detection of various biomarkers, which enabled the avoidance of interference from the biological matrix autofluorescence and photon scattering. By marrying X-ray luminescence probes with stimuli-responsive materials, multifunctional theragnostic nanosystems were constructed for on-demand synergistic gas radiotherapy with excellent therapeutic effects. By taking advantage of the capability of X-rays to penetrate the skull, we also demonstrated the development of controllable, wireless optogenetic neuromodulation using X-ray luminescence probes while obviating damage from traditional optical fibers. Furthermore, we discussed in detail some challenges and future development of X-ray luminescence in terms of scintillator synthesis and surface modification, mechanism studies, and their other potential applications to provide useful guidance for further advancing the development of X-ray luminescence.

Electronic structures and photophysical properties of carbazole‐ and thiophene‐based organic compounds used as hole‐injecting layer for organic light‐emitting diodes (OLEDs)

AbstractIn this study, we have carried out a theoretical study on six organic compounds based on thiophene and carbazole, with the aim of using them as a hole‐injecting layer of organic light‐emitting diodes (OLEDs). In this study, we have tested two types of structures: D‐π‐D for MO1, MO2, MO3, and MO4 compounds and D‐π‐A for MO5 and MO6 compounds. The correlation structure‐properties of these studied compounds have been proceeded and discussed by analyzing highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), energy gap, polarization effect, atom transition density matrix, absorption, and photoluminescence (PL). This theoretical study, based on density functional theory (DFT)/TPSSTPSS/aug‐cc‐pVQZ and the integral‐equation‐formalism polarizable continuum model/Coulomb attenuated method‐Becke, 3‐parameter, Lee–Yang–Parr (IEFPCM/TD‐CAM‐B3LYP)/6‐31++G(d,p) is consolidated by experimental data for MO1, MO2, and MO4 compounds, allowing the determination of their structural and optoelectronic properties (HOMO, LUMO, gap [Eg], absorption, and emission parameters). The obtained results appear very conclusive and show that the performance of these compounds in terms of luminescence, absorption, and current–voltage (I–V) characteristics of OLED devices make them a promising candidate for the realization of light‐emitting diodes.

A heterovalent doping strategy induced efficient cyan emission in Sb3+-doped CsCdCl3 perovskite microcrystal for solid state lighting

Metal halides can produce a broadband emission spectrum of self-trapped excitons (STEs) with a large stokes shift because they have strong electron-phonon coupling and soft lattice. In this study, CsCdCl3:xSb3+ perovskite microcrystals were prepared using a simple co-precipitation strategy at room-temperature. Their composition, morphology and phase structure were characterized by EDS, XPS, SEM and XRD. The result showed that the structure of the CsCdCl3:xSb3+ perovskite microcrystals was hexagonal. In terms of luminescence, the un-doped CsCdCl3 sample showed a quite broadband emission from the host STEs with a large Stokes shift of 340 nm. The PLE and PL of the CsCdCl3:0.007Sb3+ sample show two absorptions at the wavelength of 300 and 355 nm, which is because of the 1S0 → 1P1 and 1S0 → 3P1 transitions of Sb3+ ions and the enhanced cyan emission from STEs emission of [SbCl6] octahedra induced by a heterovalent doping strategy, respectively. In addition, in the PL spectra, there are two luminescence centers in the CsCdCl3:xSb3+ samples. The emission peak at 500 nm is higher than that at 600 nm, which can be attributed to the STEs of [SbCl6] and the two face-sharing octahedra [Sb2Cl9], respectively. The formation of STEs can be demonstrated by the large S value. The CsCdCl3:xSb3+ samples undergo two thermal processes, with an activation energy of 127 meV (Ea2) at a high temperature and 101 meV (Ea1) at a low temperature. Finally, they have good thermal and anti-water stability, and thus can be possibly applied in white LED with CIE color coordinates of 0.4119 and 0.3897, the CCT of 3227 K and CRI of 79.3.

Ratiometric Luminescence Detection of Copper(I) by a Resonant System Comprising Two Antenna/Lanthanide Pairs.

Selective and sensitive detection of Cu(I) is an ongoing challenge due to its important role in biological systems, for example. Herein, we describe a photoluminescent molecular chemosensor integrating two lanthanide ions (Tb3+ and Eu3+) and respective tryptophan and naphthalene antennas onto a polypeptide backbone. The latter was structurally inspired from copper-regulating biomacromolecules in Gram-negative bacteria and was found to bind Cu+ effectively under pseudobiological conditions (log KCu+ = 9.7 ± 0.2). Ion regulated modulation of lanthanide luminescence in terms of intensity and long, millisecond lifetime offers perspectives in terms of ratiometric and time-gated detection of Cu+. The role of the bound ion in determining the photophysical properties is discussed with the aid of additional model compounds.

Radioluminescence Response of Ce-, Cu-, and Gd-Doped Silica Glasses for Dosimetry of Pulsed Electron Beams.

Radiation-induced emission of doped sol-gel silica glass samples was investigated under a pulsed 20-MeV electron beam. The studied samples were drawn rods doped with cerium, copper, or gadolinium ions, which were connected to multimode pure-silica core fibers to transport the induced luminescence from the irradiation area to a signal readout system. The luminescence pulses in the samples induced by the electron bunches were studied as a function of deposited dose per electron bunch. All the investigated samples were found to have a linear response in terms of luminescence as a function of electron bunch sizes between Gy/bunch and Gy/bunch. The presented results show that these types of doped silica rods can be used for monitoring a pulsed electron beam, as well as to evaluate the dose deposited by the individual electron bunches. The electron accelerator used in the experiment was a medical type used for radiation therapy treatments, and these silica rod samples show high potential for dosimetry in radiotherapy contexts.

Peasecod-Like Hollow Upconversion Nanocrystals with Excellent Optical Thermometric Performance.

Trivalent lanthanide (Ln3+)‐doped hollow upconversion nanocrystals (UCNCs) usually exhibit unique optical performance that cannot be realized in their solid counterparts, and thus have been receiving tremendous interest from their fundamentals to diverse applications. However, all currently available Ln3+‐doped UCNCs are solid in appearance, the preparation of hollow UCNCs remains nearly untouched hitherto. Herein, a class of UCNCs based on Yb3+/Er3+‐doped tetralithium zirconium octafluoride (Li4ZrF8:Yb/Er) featuring 2D layered crystal lattice is reported, which makes the fabrication of hollow UCNCs with a peasecod‐like shape possible after Ln3+ doping. By employing the first‐principle calculations, the unique peasecod‐like hollow nanoarchitecture primarily associated with the hetero‐valence Yb3+/Er3+ doping into the 2D layered crystal lattice of Li4ZrF8 matrix is revealed. Benefiting from this hollow nanoarchitecture, the resulting Li4ZrF8:Yb/Er UCNCs exhibit an abnormal green upconversion luminescence in terms of the population ratio between two thermally coupled states (2H11/2 and 4S3/2) of Er3+ relative to their solid Li2ZrF6:Yb/Er counterparts, thereby allowing to prepare the first family of hollow Ln3+‐doped UCNCs as supersensitive luminescent nanothermometer with almost the widest temperature sensing range (123–800 K). These findings described here unambiguously pave a new way to fabricate hollow Ln3+‐doped UCNCs for numerous applications.

Sodium sulfite leads to the formation of fluorescent organic nanoparticles: Regulation from aqueous solution, cellular pathway to security design patterns

Fluorescent organic nanoparticles (FONs) play important roles in the monitoring and controls of biological systems. To fulfill such duties, we have to investigate how the nanoplatforms interact with living matters. Currently, very limited information concerning the potential risks and toxicity has been reported for FONs except the MTT assay. In this contribution, the amine-rich cationic precursor (polyethyleneimine) initiates one-pot copolymerization with methyldopa sesquihydrate and water-soluble fluorescent nanoparticles are afforded. The influence of reduction agent (sodium sulfite) on the luminescence, microstructure and crystallinity has been discussed and the corresponding stabilities are substantially improved. Further studies reveal that selective Cu2+ detection has been realized due to “on-off” change and the limit of detection is determined to be 52 nM. It has been discovered that glutathione (GSH) can recover its green luminescence in terms of strong affinity of GSH to copper ions. For the first time, three different cell viability experiments including MTS assay, Annexin V-APC/7-AAD kit and double stain technique have been performed to support the negligible cytotoxicity of FONs in living cells. Spectra imaging has been employed for the identification of Cu2+ and GSH in HeLa cells. In addition, the Cu2+-GSH pairs can generate an “AND” logic gate during recognition sequence operations. It will be the first example that the effectiveness of encryption and decryption has been verified via Cu2+ and GSH based on FONs.

Neural network approach to quality monitoring of injection molding of photoluminescent polymers

Photoluminescent polypropylene was obtained by twin-screw extrusion, the engineered material was injection molded and the resulting flat components were characterized in terms of luminescence and mechanical properties. Different pigment concentrations and different thickness of molded samples were considered. Instrumented flat indentations were performed, stating good mechanical performance (more than 500 N indentation load at 0.3 mm penetration depth) of components, which showed at the same time a reliable photoluminescent emission over a reasonable time range (persistence time 30 min). The experimental trend of load-penetration curves was modelled by an artificial neural network. A good generalization capability and high flexibility were found for the proposed neural network solution.

New conjugated organic matrix-carbon nanotube functionalization: DFT modeling and spectroscopic analysis

The materials referred to in this work are two cyano oligo-phenylene-vinylenes, soluble in chloroform, possessing donor and acceptor groups with a completely extended π-electron system on the whole chain. For a better description of the correlation structure-properties of these new materials, we proceeded via spectroscopic analyses and experiment techniques, such as thermogravimetric analysis (TGA), infrared spectroscopy (IR), optical absorption (OA) and photoluminescence (PL). This experimental study is consolidated by a theoretical study, based on the Density Functional Theory (DFT/B3LYP/6-31G(d,p)), allowing the determination of their structural and optoelectronic properties (conformation, gap (Eg), stabilization energy (Estab), ionization potential (IP), electron affinity (EA), absorption and emission parameters). These results, confronted with the experimental ones, appear very conclusive and show that the performance of these materials in terms of luminescence, absorption, thermal and environmental stability, make the DOMCNcompound a promising candidate for the realization of light emitting diodes.For a better correlation structure-properties and in order to further improve the properties of the active layer, the DOMCN is functionalized with two single-walled carbon nanotubes (SWCNT): SWCNT(5,5) and SWCNT(6,4) for the sake of comparison. This non-covalent functionalization route is manifested by a pre-organization governed by Van der Waals in a π-stacking interaction between the SWCNT and the organic matrix. Additionally, preliminary results on the diagrams energy and injection barriers in the organic light-emitting diodes (OLEDs) are highlighted and discussed.

Effects of CdS quantum dot in polymer nanocomposites: In terms of luminescence, optic, and thermal results

CdS quantum dots (QDs) which have unique luminescence efficiency were synthesized by two-phase method using oleic acid (OA) as a surfactant. The nanocomposites have been obtained by blended CdS quantum dots with low-density polyethylene (LDPE) in different ratios. Primarily, radioluminescence (RL) properties were investigated as well as their structural (FT-IR, XRD), morphological (TEM, SEM), thermal (TG-DTA) and absorption (UV–Vis) properties of these nanocomposites. The RL peaks of OA-capped CdS QD were observed at 456 nm and 655 nm. As a consequence of the nanocomposites being doped with powder CdS QD, a significant blue shift was observed in the absorption bands. The optical band gap of CdS was calculated as ̴ 2.3 eV. The nanocomposites blended with CdS QD, this value increased to ̴ 2.7 eV. It has also been observed that nanoparticles cause nanocomposites to have lower melting temperatures.

Luminescence of silicon nanoparticles from oxygen implanted silicon

Oxygen with a kinetic energy of 20 keV is implanted in a silicon wafer (100) at different fluences, followed by post-implantation thermal annealing (PIA) performed at temperatures ranging from 1000 to 1200 °C, in order to form luminescent silicon nanoparticles (SiNPs) and also to reduce the damage induced by the implantation. As a result of this procedure, a surface SiOx layer (with 0 < x < 2) with embedded crystalline Si nanoparticles has been created. The samples yield similar luminescence in terms of peak wavelength, lifetime, and absorption as recorded from SiNPs obtained by the more conventional method of implanting silicon into silicon dioxide. The oxygen implantation profile is characterized by elastic recoil detection (ERD) technique to obtain the excess concentration of Si in a presumed SiO2 environment. The physical structure of the implanted Si wafer is examined by grazing incidence X-ray diffraction (GIXRD). Photoluminescence (PL) techniques, including PL spectroscopy, time-resolved PL (TRPL), and photoluminescence excitation (PLE) spectroscopy are carried out in order to identify the PL origin. The results show that luminescent SiNPs are formed in a Si sample implanted by oxygen with a fluence of 2 × 1017 atoms cm−2 and PIA at 1000 °C. These SiNPs have a broad size range of 6–24 nm, as evaluated from the GIXRD result. Samples implanted at a lower fluence and/or annealed at higher temperature show only weak defect-related PL. With further optimization of the SiNP luminescence, the method may offer a simple route for integration of luminescent Si in mainstream semiconductor fabrication.

Temporal and Remote Tuning of Piezophotonic-Effect-Induced Luminescence and Color Gamut via Modulating Magnetic Field.

Light-emitting materials have been extensively investigated because of their widespread applications in solid-state lighting, displays, sensors, and bioimaging. In these applications, it is highly desirable to achieve tunable luminescence in terms of luminescent intensity and wavelength. Here, a convenient physical approach of temporal and remote tuning of light-emitting wavelength and color is demonstrated, which is greatly different from conventional methods. It is shown that by modulating the frequency of magnetic-field excitation at room temperature, luminescence from the flexible composites of ZnS:Al, Cu phosphors induced by the piezophotonic effect can be tuned in real time and in situ. The mechanistic investigation suggests that the observed tunable piezophotonic emission is ascribed to the tilting band structure of the ZnS phosphor induced by magnetostrictive strain under a high frequency of magnetic-field excitation. Furthermore, some proof-of concept devices, including red-green-blue full-color displays and tunable white-light sources are demonstrated simply by frequency modulation. A new understanding of the fundamentals of both luminescence and magnetic-optics coupling is thus provided, while offering opportunities in magnetic-optical sensing, piezophotonics, energy harvesting, novel light sources, and displays.

The radioluminescence and optical behaviour of nanocomposites with CdSeS quantum dot

In this work, highly luminescent alloyed CdSeS QDs are successfully synthesized by two phase route method by using oleic acid (OA) as a surfactant. OA capped CdSeS QDs prepared in two different synthesis duration were compared in terms of luminescence and optical properties.The nanocomposites blended with CdSeS QDs which have highly luminescent efficiency in different ratios by Low Density Polyethylene (LDPE) and these nanocomposites were mainly investigated radioluminescence (RL) and optical properties (UV/VIS absorption). Structural, morphological, thermal properties of the nanocrystal and nanocomposites were examined using; XRD, FT-IR, TEM, SEM, TG-DTA techniques.OA capped CdSeS and also nanocomposites were showed two RL spectrum peaks in green and red region at around 528nm and 710nm respectively. Also, it is seen that the radioluminescence intensity changes linearly with the particle size of the QDs and about 12% size change of quantum dot led to a threefold increase in RL intensity. The luminescence glow curves are in compliance with absorption and fluorescence spectra.The absorption bands showed a significant blue shift for the nanocomposites as compare to powder CdSeS. The optical band gap of the OA capped CdSeS calculated as 1.77 eV. It was observed that the optical band gap of LDPE was decreased by the adding ratio of CdSeS from 3.71eV to 2.25eV.

Physical basis of persistent luminescence: The case of europium doped Ca1−xSrxS

The physical basis of persistent luminescence in terms of the color of emission as well as the useful afterglow time is discussed for a commercial red-emitting Ca1−xSrxS:Eu phosphor. The discussion is based on the results of excitation/emission spectra and critical analysis of thermoluminescence (TL) data. The work focuses on: (i) the well known tuning of emission in Ca1−xSrxS:Eu phosphor (ii) control of intrinsic trapping parameters that decides the lifetime (τ) of charge in traps relevant to the phenomenon of persistent luminescence. XRD data is used to characterize the commercial phosphor. The emission spectra (λex = 275 nm) reveals the prominent well known broad emission (FWHM = 0.20 eV) at 1.92 eV/647 nm of Eu2+ along with weak transitions at 1.63 eV/761 nm, 1.75 eV/710 nm, 2.13 eV/581 nm and 2.56 eV/485 nm indicating presence of europium in Eu3+ state. Rigorous analysis of TL shows that non-first order TL peaks having τ300≈mins to hours are key to persistent luminescence in Ca1−xSrxS:Eu.

Fracturation des carbonates dans la zone de faille normale active d’Aigion (Grèce) à partir des carottes du puits: conséquences sur les propriétés de transfert de fluides

Abstract La faille d’Aigion appartient à un système de failles normales à pendage nord affectant la bordure sud du golfe de Corinthe, témoin d’une extension active d’échelle régionale caractérisant la région égéenne. Les carottes du forage AIG-10, qui a traversé cette faille, montrent la présence d’une zone endommagée et d’une gouge. Ce travail présente une analyse des lames minces faites à partir de ces carottes. Il confirme la zonation en termes de fracturation à l’approche de la faille. Loin de cette dernière, la fracturation héritée de la phase compressive de l’orogenèse hellénique est dominante, bien qu’il existe aussi une famille E-W liée à l’extension actuelle. Toutes ces fractures sont scellées et le remplissage est similaire d’un point de vue luminescence au calcaire hôte. A l’approche du coeur, la quantité de fractures liées à la faille augmente; le remplissage de ces fractures indique, en cathodoluminescence, le passage de plusieurs fluides qui seraient d’origine externe, et la dernière génération de fractures est encore ouverte. Au mur de la faille, sous 5 m d’épaisseur verticale de cataclasite et d’ultracataclasite dans les calcaires et radiolarites (coeur de faille) et 13 m d’épaisseur verticale de gouge dans les radiolarites, les observations sont plus limitées, car la présence d’un karst a restreint les possibilités de carottage. Néanmoins, on peut observer que le remplissage des fractures liées à l’extension est différent de ce qui nous a été dévoilé au toit. Ceci suggère que la faille, transversalement imperméable aujourd’hui, l’a toujours été. L’analyse de la succession des ciments met en évidence une perméabilité parallèle à la faille à la faveur d’un système de fractures et fentes jeunes et ouvertes, pendant qu’est discuté le transfert de fluides par rapport aux stades de propagation de la faille.

Multi-modal luminescence properties of RE3+ (Tm3+, Yb3+) and Bi3+ activated GdNbO4 phosphors—upconversion, downshifting and quantum cutting for spectral conversion

This work investigates the promising multi-modal luminescence (upconversion (UC), downshifting (DS) and quantum cutting (QC)) properties of RE3+ (Tm3+, Yb3+) and Bi3+ activated GdNbO4 phosphors synthesized using the well-known solid state reaction method. Structural characterization using x-ray diffraction measurements confirms the formation of the pure phase of the GdNbO4 host with no impurities. The optical band gap (Eg) of GdNbO4 (with and without RE3+ ions) calculated from UV–Vis–near-infrared (NIR) measurements was found to be the same ~4.44 eV which indicates that GdNbO4 is a wide band gap material. Further, Bi3+ doping presents an interesting Eg tuning of the GdNbO4 phosphor, i.e. Eg increases up to 5.38 eV. In terms of luminescence, this material produces intense blue and NIR emission via multi-modal optical processes. On NIR excitation (λexc = 980 nm), Gd0.94Tm0.01Yb0.05NbO4 produces intense upconverted blue and NIR and relatively weak red emission. In addition to the UC process, Gd0.94Tm0.01Yb0.05NbO4 also exhibits pump power dependent variation in fluorescence intensity ratio for I472/I477 showing the applicability of this material as an optical heater. On UV excitation (λexc = 265 nm), Gd0.99Tm0.01NbO4 produces intense DS blue emission due to the Tm3+ ion, overlapped with the emission of the (NbO4)3− ion through strong energy transfer (ET) from (NbO4)3− to Tm3+ ions. Interestingly, NIR QC has also been successfully observed in Gd0.9Yb0.1NbO4, Gd0.89Bi0.01Yb0.1NbO4 and Gd0.79Tm0.01Yb0.2NbO4 phosphors through cooperative ET from the (NbO4)3− group to the Yb3+ ion, Bi(6s)–Nb(4d) to the Yb3+ ion and the Tm3+ ion to the Yb3+ ion, respectively. The mechanisms involved in these processes are explained in detail in this work. The QC efficiency in this work has been found to be ~177%. Thus, the multi-modal luminescence (UC, DS and QC) property of this material makes it a promising candidate for display devices, spectral converters for enhancing the efficiency of silicon solar cells, etc.

Optical, structural, and morphological characterisation of epitaxial ZnO films grown by pulsed-laser deposition

We report on ZnO epitaxial growth by pulsed-laser deposition (PLD) on different substrates, such as quartz, sapphire, and GaN template. Approximately 1μm-thick films were grown under different substrate temperatures and background oxygen conditions. X-ray diffraction analysis indicated preferential growth along the c-axis direction with a full-width at half maximum (FWHM) of the rocking curve as narrow as 230arcs in the case of the GaN template. Low-temperature photoluminescence showed A-excitonic emission near 3.36eV and a FWHM of D0XA emission as small as 2.89meV at 9K. Atomic force microscope measurements showed that roughness as low as 18nm could be obtained. These results prove that PLD is a low-cost technique suitable to grow heteroepitaxial ZnO layers with excellent properties in terms of luminescence, crystallinity and morphology.