Visible Luminescence Research Articles

Intense Continuous Wave Laser to Synthesize Luminescent Solution of Carbon Dots

Biocompatible Carbon dots (CDs) were obtained by the laser irradiation of vegetable carbon placed in a Phosphate-Buffered Saline (PBS) solution. The carbon nanoparticles were generated by a visible and continuum wave (CW) He-Ne laser beam at a 632.8 nm wavelength with 1 mm2 spot, irradiating the carbon target for times of the order of some hours. The CDs generation might be due to thermal effects induced by the prolonged laser irradiation inducing carbon atoms ejection bounded by weak van de Walls forces. Ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infrared spectroscopy (FTIR) transmittance and luminescence measurements were employed to study the CDs synthesize. The UV excitation at a 365 nm wavelength induces visible CDs luminescence mainly at about 474 nm wavelength, giving the emitted light a characteristic blue color. The CDs luminescence in biocompatible solutions is presented and discussed in anticipation of possible applications in various sectors, such as radiation detector and material physics, engineering, microelectronics, sensors and, above all, in relation to bio-images from cell cultures and biological tissue as possible applications to the bio-medical field.

Sputtering Deposition of ZnO Thin Films for Photocatalytic Hydrogen Production: Perspectives on Upscaling

This study presents the successful implementation of ZnO thin films (denoted as z01, z02, and z03) through magnetron sputtering in the photocatalytic production of hydrogen using a low-intensity UV source (3 mW cm−2). The one-step synthesis process demonstrates simplicity and scalability. The deposited coatings, with thicknesses ranging from 62 to 209 nm, exhibit a hexagonal crystalline structure and display visible luminescence in the yellow-red range, attributed to point defects in the ZnO lattice. Among the samples, z03 (62 nm in thickness) exhibited the most promising performance in photocatalytic hydrogen production, achieving a rate of (5387.2 ± 151.6) µmol g⁻¹ h⁻¹ when utilizing methanol as a hole scavenger. These findings hold great potential for upscaling such coatings in energy harvesting applications. The present work opens new avenues for efficient and scalable hydrogen production, contributing to improving clean energy technologies.

Visible and NIR steady-state luminescence properties of Dy3+ ions-doped calcium phosphate glasses for light-emitting diodes

In this paper, we systematically investigate photoluminescence attributes of dysprosium (Dy3+) ions-doped calcium phosphate, (99-x) P2O5 + x CaO + 1.0 Dy2O3 (x = 20, 30 and 40) (CaPDy) glass samples fabricated via the melt-quenching method. The luminescence emission spectra unveiled the visible emission at 484 nm and 573 nm and near-infrared emission at 1011 nm under the excitation wavelength of 349 nm. The emission decay kinetic studies reveal that the decay profiles exhibit non-exponential behaviour. Furthermore, the CIE chromaticity coordinates, and the ratio of Y/B using 573 nm 484 nm emission intensities were evaluated and further utilized to estimate the CCT values. The results show that the studied glass samples has potential for the yellowish cool light applications.

The effects of delayed annealing on the luminescent activity of heavy metal cadmium zinc phosphate glasses activated by: Er3+ and Tb3+ ions

The luminescent spectra of the RE2O3-doped P2O5–CdO–ZnO glasses (RE = Er, and Tb) were investigated to separate the effects of two studied rare-earth elements and the annealing regime on the emission performance of the prepared glasses. The glasses undergo a series of collective measurements including UV–visible absorption, luminescence, thermal expansion, XRD, TEM, and FTIR. The optical UV–visible spectra of the two doped glasses reveal a UV band due to undoped glass beside and extra extended 11 peaks with the Er3+ ions with high distinct features while the Tb3+ ions samples exhibit peaks within the visible region. These peaks are correlated with transitions from the ground state in each case to specific energy transitions. The overall optical data indicate that the two rare earth ions are present in a stable trivalent state. Under UV excitation, both Er3+ and Tb3+ emit a characteristic green light corresponding to 4S3/2 → 4I15/2 and 5D4 → 7F5 transitions, respectively. The performance of the green light was identified to be enhanced by increasing the concentration of rare earth and the effect of annealing temperature. Moreover, the intensity of the infrared emission of Er3+ at 1532 nm corresponds to the (4I13/2 → 4I15/2) transition which is assumed to be developed with the effect of heating. The resultant IR spectra show distinct vibrational peaks due to phosphate groups that undergo only minor modifications when doped with rare earth elements or over-annealed.

Observation of Visible Upconversion Luminescence of Soft Glass Multimode Fibers

This research investigates the visible upconversion luminescence which is induced by multiphoton absorption of soft glass fiber defects. The study of this phenomenon has thus far been restricted to standard silica fibers. We observed the emission of green and cyan light as a consequence of fiber material ionization. We investigate both the commercial ZBLAN step index and in-house-made tellurite nanostructured graded-index fibers. For the latter, the analysis of the luminescence signal permits us to determine the core and cladding refractive index difference. Upconversion luminescence is a powerful tool for characterizing soft glass fibers and a promising platform for innovative photonic technologies and mid-IR applications.

Investigation of visible emission and luminescence center evolution in Pr–La:CaF2 single crystals for laser application

The study presents Pr,La:CaF2 single crystals grown using the temperature gradient technique, showing distinct Pr3+–La3+ cluster types, with two types of centers showing cubic symmetry.

Aminopropyl triethoxy silane capped ZnO quantum dots for highly selective dopamine

Quantum dots (QDs) can be used as labels with fluorescent nanoprobes and ZnO QDs have band gap over 4 eV with a large 60 meV exciton binding energy. Capped ZnO presents high quantum efficiency and surface enhancement in biochemical analysis and ultrasensitive detection of biomaterials and proteins. This work reported the synthesis of ZnO QDs capped with different agents of 3-aminopropyl triethoxy silane (APTES), tetraethyl orthosilicate (TEOS) and dimethyl sulfoxide (DMSO) from nonaqueous medium. ZnO QDs were characterized by different techniques of UV-vis absorption spectra, fluorescent emission spectra, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Zeta potential and high-resolution transmission electron microscopy (HRTEM). Photoluminescence (PL) emissions illustrated that APTES capped ZnO QDs have the highest PL intensity and applied as an optical sensor for dopamine (DA) determination in an aqueous solution and real serum samples. The visible luminescence of ZnO may result from either the recombination of a delocalized electron with a deeply trapped hole or the recombination of a delocalized hole with a deeply trapped electron. Zeta potential values showed that the surface potentials of - 4.23, -7.70, -14, -1.94 mV for uncapped ZnO, DMSO, APTES capped, TEOS capped ZnO QDs, respectively. The fluorescence quenching observed in ZnO QDs primarily stemmed from electron transfer between the ZnO QDs and two variants of dopamine: reduced dopamine acting as electron donors and oxidized dopamine-quinone serving as electron acceptors. APTES capped ZnO QDs probe exhibited a linear dynamic range from 6.2 – 0. 195 nM of DA with correlation coefficient (R2) of 0.99, limit of detection (LOD) of 0.2 nM and a sensitivity of 406.6 µM-1.

Short-time X-ray irradiation induced long afterglow and photostimulated luminescence from Sr2GeO4: Pr3+

In this paper, Short-time X-ray irradiation induced long afterglow and photostimulated luminescence from Sr2GeO4: Pr3+ has been observed. Under the X-ray irradiation, Sr2GeO4: Pr3+ can produce long afterglow and photostimulated visible luminescence mainly located at 490, 547 and 629 nm, which are attributed to 3P0→3H4, 3P0→3H5 and 3P0→3H6 of Pr3+, respectively. More important, even 5 s X-ray irradiation which was less than the X-ray damage from one CT scan, can induce 5400 s afterglow emission. Furthermore, due to its excellent photostimulated luminescence properties, the afterglow emission intensity of Sr2GeO4: Pr3+can be significantly improved under the radiation of 980 and 808 nm lasers and the emission intensities can still be maintained even after 12 testing cycles. The thermoluminescence results show that Pr3+ doping produces three different traps. Among these, the traps with 0.64 and 0.71 eV trap depth result in excellent X-ray long afterglow luminescence of Sr2GeO4: Pr3+. While the deep trap of 0.96 eV determines the photostimulated luminescence properties. These results indicate that Sr2GeO4:Pr3+ possesses excellent long afterglow and photostimulated luminescence under the X-ray irradiation in safety range, which thus can be regarded as in vivo light source to efficiently conduct photodynamic therapy in the future.

Melt-grown semi-insulating Mn:β-Ga2O3 single crystals exhibiting unique visible absorptions and luminescence

Several acceptor dopants have been explored in β-Ga2O3 to produce semi-insulating substrates and epitaxial films. Fe and Mg make up the majority of research thus far; however, other transition metals provide potential alternatives for optimized performance. β-Ga2O3 bulk single crystals were grown by the Czochralski and vertical gradient freeze methods with a nominal dopant concentration of 0.25 at. % Mn. Ultraviolet-visible-near infrared spectroscopy and photoluminescence revealed polarization- and orientation-dependent optical absorptions (pleochroism) coupled with an orange luminescence. All samples were electrically insulating, on the order of 109–1011 ohm cm at room temperature, indicative of acceptor doping. Actual dopant concentrations of the intentionally doped transition metal and background impurities were determined via glow discharge mass spectrometry, indicating the macroscale segregation behavior. High-temperature resistivity measurements indicated an experimental acceptor level of 1.7 ± 0.2 eV. Hydrogenation of samples resulted in an increase in the orange luminescence and O–H stretching modes observable in the infrared spectrum. Density functional theory calculations were performed to determine the likely site-occupancy and acceptor level of Mn in the bandgap.

Effect of Eu3+ ions concentration on visible red luminescence and radiative shielding properties of SrO–Al2O3– BaCl2–B2O3– TeO2 glasses

Trivalent europium (Eu3+) ions doped 10SrO-(10-x)Al2O3–10BaCl2–60B2O3–10TeO2 glasses were fabricated by the melt-and-quenching technique and characterized for excitation, absorption, emission, decay methods to analyze the suitability of the glasses for photonic device applications. In addition, gamma attenuation data of the prepared glasses were Obtained for energies 15 keV ≤ E ≤ 10 MeV using FLUKA and XCOM methods to check their suitability for radiative shielding purposes. Direct allowed, indirect allowed band gaps and Urbach energies were estimated from absorption spectra. Emission spectra obtained for an excitation wavelength of 362 nm have been used to estimate J-O intensity parameters Ωλ (where λ = 2, 4). The intensity parameters Ω2 and Ω4 were again used to evaluate various radiative properties for the emission transition 5D0→7F2 of Eu3+ ions doped OCBT glasses. Decay curves were well fitted by single exponential and in turn used to estimate experimental lifetime (τexp) of metastable state (5D0) of Eu3+ions. The analysis on radiative properties showed that 2.5 mol % of Eu3+ ions activated OCBT glasses for the emission transition 5D0→7F2 is well suitable for visible red lasers and display applications. Analysis of evaluated interaction parameters for gamma radiation fast and thermal neutrons showed clear cut dependence on the Eu2O3 content of the glasses. In addition, the radiation absorption ability of the glasses was compared with different classes of concrete, commercial glass shields, and nonconventional shielding materials. The present glasses showed great potential for deployment in radiation absorption roles in nuclear technologies.

An Achaemenid God in Color

A limestone relief fragment with a figure in a winged disk from the fifth-century BCE Hall of 100 Columns at Persepolis in southwestern Iran that entered the Harvard Art Museums’ collections in 1943 preserves significant traces of its original coloration and has played a key role in the rediscovery of polychromy at the Achaemenid Persian capital. After tracing the fragment’s journey to Cambridge, MA, this article presents the results of recent technical studies of its pigment remains, including visible light-induced infrared luminescence (VIL) imaging, X-ray fluorescence (XRF) spectroscopy, and the analysis of micro samples by Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and polarizing light microscopy (PLM). The new scientific data is compared to the findings of ongoing investigations of polychromies at Persepolis and other Achaemenid Persian sites and evaluated for the information it can and cannot provide on the original appearance of the figure in the winged disk, likely the Zoroastrian god Ahuramazda. The article reviews past attempts at reconstructing the relief’s coloration and the assumptions that guided them, recounts the experience of creating a tangible three-dimensional color reconstruction for an exhibition, and concludes with some general thoughts on the valuation of colorfulness.

Effect of Plasma Treatment on the Luminescent and Scintillation Properties of Thick ZnO Films Fabricated by Sputtering of a Hot Ceramic Target

The paper presents the results of a comprehensive study of the structural-phase composition, morphology, optical, luminescent, and scintillation characteristics of thick ZnO films fabricated by magnetron sputtering. By using a hot ceramic target, extremely rapid growth (~50 µm/h) of ZnO microfilms more than 100 µm thick was performed, which is an advantage for the industrial production of scintillation detectors. The effects of post-growth treatment of the fabricated films in low-temperature plasma were studied and a significant improvement in their crystalline and optical quality was shown. As a result, the films exhibit intense near-band-edge luminescence in the near-UV region with a decay time of <1 ns. Plasma treatment also allowed to significantly weaken the visible defect luminescence excited in the near-surface regions of the films. A study of the luminescence mechanisms in the synthesized films revealed that their near-band-edge emission at room temperature is formed by phonon replicas of free exciton recombination emission. Particularly, the first phonon replica plays the main role in the case of optical excitation, while upon X-ray excitation, the second phonon replica dominates. It was also shown that the green band peaking at ~510 nm (2.43 eV) is due to surface emission centers, while longer wavelength (>550 nm) green-yellow emission originates mainly from bulk parts of the films.

Temperature measurements based on a composite of nanosized phosphors [Ru(dipy)<sub>3</sub>]<sup>2+</sup>@SiO<sub>2</sub> and NaYF<sub>4</sub>:Eu,Gd

The results of temperature testing of the two-phosphor composite ([Ru(dipy)3]2+@SiO2 and NaYF4:Eu,Gd) are presented in order to assess the prospects for its further application as a luminescent thermal sensor in the range of 200–310 K. By calibrating the temperature dependences of individual spectral components of the emission produced under irradiation by cw laser at 405 nm, the possibilities of temperature sensing by means of ratiometric method are analyzed in four different spectral ranges of the composite’s visible luminescence.

Enhanced emission and reactive oxygen species generation of GdOF: Yb3+, Er3+ nanomaterial under ambient dark conditions

Yb3+ and Er3+ co-doped GdOF nanomaterials were synthesized using a urea-based co-precipitation method followed by calcination at 500 °C under a nitrogen atmosphere. The structural characteristics and crystallite size were determined through Rietveld refinement of X-ray powder diffraction measurements. The impact of doping concentration on the shape, size, and morphology was thoroughly investigated and discussed. The average crystallite size of the material falls within the range of 10–19 nm. Vibrational modes corresponding to desired bonds were characterized using FTIR spectroscopy. Visible luminescence spectra were recorded under 390 nm excitation. The visible luminescence property is attributed to the contribution of Er3+. The detailed luminescence mechanism was thoroughly discussed. The luminescence properties were analyzed in relation to varying concentrations of Er3+ ions (while maintaining a fixed Yb3+ concentration), with comprehensive discussions provided. Building upon the luminescent characteristics of these materials, investigations were conducted into the generation of reactive oxygen species, both experimentally and theoretically. In conclusion, the photoluminescence study indicates that the synthesized material holds significant promise for applications in oxidative stress-induced therapeutic processes and versatile bioimaging purposes.

Effects of surface conditions on the visible luminescence of ZnO

The effects of surface conditions on photo-induced-carrier (PIC) diffusion are studied by solving one-dimensional continuity equation. Using various forms of ZnO samples with different surface conditions, the PICs lost at sample surface are substantiated to have important contributions to the visible luminescence. For unpassivated ZnO nanorods and single-crystal samples that undergo a high-temperature annealing in air, the visible luminescence originating from the PICs diffused to the surface is estimated more than 99.8 % and 70 % at room temperature, respectively, and more than 99.99 % and 97 % at low temperature. The structureless luminescence caused by PICs, such as the green, yellow, and orange luminescence bands are well fitted under the framework of tail-state luminescence, while the structured green band is suggested to be in association with a specific type of surface states formed during high-temperature annealing in oxidizing atmosphere and can be fitted with Huang-Rhys model by taking into account tail-state luminescence.

Sensitizing visible and near-infrared lanthanide (Ln3+ = Er3+/Ho3+) luminescence within a semiconductor Sr2CeO4 host

Sensitizing visible and near-infrared lanthanide (Ln3+ = Er3+/Ho3+) luminescence within a semiconductor Sr2CeO4 host

Emission characteristics, crystalline phase and composition of Er3+/Yb3+ doped LiNbO3 thin films deposited by e-beam evaporation

Er3+/Yb3+ doped LiNbO3 (LN) single crystal films with varying Yb3+ doping level were grown on z-cut LiTaO3 bulk single crystals via using e-beam evaporation method. The crystallographic orientation, elemental distribution, fluorescence properties, ionic valence states, Er3+ concentration, Yb3+ concentration and Li2O content of films were carefully studied. Results from XRD, SEM and Raman scattering conclude that the predominant phase of these films is LN and they are oriented along (006). The results of energy dispersive spectroscopy indicate that constituent elements are uniformly distributed over the entirety of the films. The visible and near-infrared luminescence intensities rise with increasing Yb3+-doping concentration. The Li2O content of films remains constant at 48.8 mol% with growing Yb3+-doping level based on the optical birefringence method, which is consistent with the Raman results. XPS results suggest that the Er3+ and Yb3+ concentrations in the films are lower than that in the polycrystalline powder since e-beam evaporation has a low efficiency of heavy Er3+ and Yb3+ ions.

Er3+/Tm3+ co-activated core@shell nanoarchitectures: tunable upconversion luminescence and high-security anti-counterfeiting

Currently, developing advanced optoelectronic materials is of great importance to solving serious problem of fake and shoddy products. Lanthanide-doped nanomaterials are particularly suitable for addressing this issue, but limited by the realization of multiple upconverison (UC) emissions upon a single-wavelength laser excitation. Herein, it is proven that the co-dopant of blue/near-infrared (NIR)-emitting activators (Tm3+) and green/red-emitting centers (Er3+) in a particular designed core–shell nanoarchitecture allows the achievement of multiple luminescence over wide spectral region for optical security. In our study, cubic-phased NaYbF4:Tm/Er@CaF2 nanocrystals have been successfully synthesized through a layer-by-layer coprecipitation strategy, which presents visible multicolor UC luminescence and invisible NIR UC emission upon 980 nm laser excitation by just regulating the laser power and temperature. Significantly, the unique luminescent characteristics enables the designed UC nanoparticles a promising candidate for advanced anti-counterfeiting. This works offers a reference to develop advanced optoelectronic materials for practical application in optical security.

Insight into the photoluminescence and morphological characteristics of transition metals (TM = Mn, Ni, Co, Cu)-doped ZnO semiconductor: a comparative study

In this work, undoped and transition metal (TM = Mn, Ni, Co, Cu)-doped ZnO thin films were grown on Si substrate using the ultrasonic spray pyrolysis technique, adhering to the same deposition conditions to compare their morphological and photoluminescent characteristics. X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), and Photoluminescence (PL) spectroscopy were used to investigate the chemical composition, morphology, and luminescence properties, respectively. XPS results indicate that Mn and Ni ions have bivalent and trivalent electronic states coexisting in the ZnO lattice, Cu ions have both monovalent and bivalent states, and Co ions have only bivalent states. Besides, there is a considerable increase in the level of oxygen vacancies observed upon TM doping. The topographic and phase-contrast AFM images, supported by their associated statistical parameters and mean height distribution histograms, reveal that TM doping increases the tendency for crystalline grains to coalesce in 3D, resulting in a more roughened surface, larger grains with prominent boundaries, increased porosity, and an inhomogeneous height distribution. PL spectra of TM-ZnO show a broadening of the ZnO band gap accompanied by different luminescence behavior compared to pure ZnO regarding both UV and visible emissions. CuZnO is characterized by a green luminescence, CoZnO and MnZnO by a red luminescence, and ZnO and NiZnO by a broad visible luminescence. The possible mechanism for defect luminescence in each TM-ZnO sample was systematically investigated. The chromaticity color coordinates of the PL emissions show that the films provide different color regions well distributed on the CIE chromaticity diagram. The findings regarding the coexistence of two valence states of TM doping, the level of oxygen vacancies, the grain coalescence process, and the luminescence characteristics are carefully correlated and discussed herein.

Influence of Annealing on the Structural, Morphological, Photoluminescence and Visible Absorption Properties of Mg Doped CuO Micro Grains.

Narrow band gap oxide materials that harvest visible light have gained considerable attention for numerous visible light mediated applications. In this current work, a typical Mg doped CuO bulk material was prepared by a simple wet chemical method. The prepared material was annealed in three different temperatures viz.; 300°C, 400 and 500°C in air atmosphere to tune the optical band gap. XRD studies reveal that the average crystallite size increases with increase in annealing temperature. FESEM images of all the samples show their bulk nature with different grain sizes and morphologies. XPS survey scan spectra exhibit photoelectron emissions of Cu2p, O1s and Mg 1s with binding energies 933.69eV, 533.41eV and 1304.2eV for all the samples and validated the effective incorporation of Mg ions into the CuO lattice. PL spectra reveal the polychromatic UV- visible luminescence bands for all the annealed samples, whereby the PL intensity is found to be decreasing as the annealing temperature increases. Finally, the band gap decreases with annealing temperature and indicates that the sample annealed at 500°C can be exploited for visible light assisted applications such as solar cells, photocatalysis and photoelectrochemical cell.