Excitation Wavelength Dependent Photoluminescence Research Articles

Excitation-wavelength-dependent photoluminescence in GaAs nanowires under high-pressure

GaAs nanowires (NWs) have wide application potential as near-infrared optical devices and the high-pressure strategy has been applied to modulate their crystal and electronic structures. As another typical thermodynamic parameter, temperature can also affect the optical performance of semiconductors. Here we report the excitation-wavelength-dependent photoluminescence (EWDP) in GaAs NWs under high-pressure conditions. The pressure for achieving the maximum photoluminescence (PL) intensity and bandgap transition from direct to indirect of GaAs NWs varies (1.7–2.7 GPa) with the wavelength of the incident lasers (633–473 nm). The Raman peak of GaAs NWs shifts towards higher frequency with increasing excitation wavelengths at the same high-pressure conditions, revealing the stronger heating effect induced by incident laser with the shorter wavelength. The relative temperature difference in GaAs NWs induced by two different lasers can be estimated up to 537 K, and the strong heating effect suppresses the light-emission efficiency in GaAs NWs. With increasing the pressure, the relative temperature difference presents a gradual declining trend and PL intensity presents an opposite trend, which relates to the pressure-induced suppression of nonradiative recombination in GaAs NWs. Our study provides insights into the mechanisms for the EWDP effect and an alternative route to modulate the high-pressure performance of nanodevices.

Efficient light-emitting diodes from emitters of TaSe2 quantum dots and pure carbon dots and carrier injection tailoring of TaSe2

Solution-processed symbiotic TaSe2 quantum dots and carbon dots (TaSe2-QDs/CDs) and pure CDs have been facilely synthesized via liquid-phase ultrasonic exfoliation and hydrothermal reaction. Symbiotic TaSe2-QDs/CDs and CDs show good film morphology and excitation wavelength-dependent photoluminescence. With CDs (TaSe2-QDs/CDs) as emitter, efficient light-emitting diodes (LEDs) are assembled, showing maximum luminance of 217 (640) cd/m2, external quantum efficiency (EQE) of 0.11 % (0.21 %), luminous efficiency of 0.135 (0.262) cd/A, and power efficiency of 0.045 (0.095) lm/W. Resonance energy transfer from CDs to TaSe2-QDs contributes to the enhanced performance in TaSe2-QDs/CDs based LED. With 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole as emitters, normal and inverted UV organic LEDs (OLEDs) are realized using TaSe2-QDs/CDs tailoring hole and electron injection, respectively. The normal (inverted) UV OLEDs show maximum radiance of 1.14 (1.3) mW/cm2, EQE of 0.89 % (0.37 %), and electroluminescence peak of 397 (395) nm. Impedance spectroscopy and current versus voltage characteristics are performed to clarify some mechanisms.

Effects of the excitation wavelength and temperature on the zero-phonon emission lineofCr:YAG.

In this work, a detailed study was conducted of the temperature and excitation wavelength-dependent photoluminescence (PL) spectra of the chromium-doped yttrium aluminum garnet (Cr:YAG) transparent ceramic. Focusing on the two sets of zero-phonon lines (ZPLs) of the 2 E→4 A 2 transition in this material, the PL spectra are discovered to evolve significantly with respect to temperature and be highly dependent on the excitation wavelength. Compared to the continuous variation behavior with temperature, an increase in the excitation wavelength leads to a blueshift of the peak position within the regions of 450nm to 465nm, 465nm to 490nm, and 490nm to 500nm, and a sharp change in the PL position at the excitation wavelengths of 465nm and 490nm. The electron-phonon coupling (EPC) effect is believed to be more sensitive to the excitation wavelength. Different excitation wavelengths involve different electronic levels participating in the light emission processes, which explains the evolution behavior of the PL peak position with respect to the excitation wavelength. Moreover, the emergence of weak peaks next to the ZPLs at particular temperatures and excitation wavelengths is also observed. This work compares the influence of the temperature and excitation wavelength to the PL properties of the Cr:YAG transparent ceramic, which promotes an advanced understanding of the luminescence behavior of the Cr:YAG transparent ceramics.

Dual emissive Ln(iii)–Ag(i) heterometallic chains based on tris(2-pyridyl)phosphine oxide

Tris(2-pyridyl)phosphine oxide has been successfully used to assemble novel 1D Ln(iii)–Ag(i) heterometallic coordination polymers demonstrating dual emission behavior and excitation wavelength dependent photoluminescence.

Study of morphological, elemental, optical and excitation wavelength dependent red photoluminescence in Eu3+ doped Li2SrSiO4 for solid state lighting

A comprehensive investigation of Eu3+ doped Li2SrSiO4 phosphors synthesized via the solid-state reaction method was conducted. XRD confirmed the crystalline phase and SEM along with and its 3D projection's observations confirmed that the phosphor particles were in the micro meter size range, indicating their suitability for applications in primary phosphor-converted LEDs. FTIR spectroscopy elucidated vibrational characteristics, while TGA, EDX and XPS analysed thermal stability, elemental composition and valence states respectively. Doping-induced band gap increase was attributed to the Moss-Burstein effect. Photoluminescence excitation studies revealed enhanced absorption at 394 nm compared to the charge transfer transition band (CTB) at 254 nm, aligning with industry-standard near-ultraviolet chips. XPS suggested two distinct Eu3+ sites in the LSS crystal, corroborated by excitation wavelength-dependent PL emission. As a result of excitation wavelengths, the magnetic-dipole transition (5D0 → 7F1) at 592 nm, the electric-dipole transition (5D0 → 7F2) at 615 nm and the induced electric-dipole transition ((5D0 → 7F3,4) at 650 and 700 nm arose. Additionally, the phosphor gave an improved conversion efficiency at 2% Eu doping. Low synthesis temperature, micro-sized particles, thermal stable, short lifetime, excitation bands at near UV to blue region, colour tunability, lower CCT, LER and similar CIE to available red phosphors are the key factors for the Li2SrSiO4:Eu3+ proving reliable red phosphor for solid state lighting.

Luminescence Properties of Fe2+:ZnSe Single Crystals Grown via a Traveling Heater Method

The luminescence properties of iron-doped ZnSe (Fe2+:ZnSe) single crystals grown via a traveling heater method have been studied via photoluminescence (PL). Nine emission bands were identified in the PL spectra of Fe2+:ZnSe single crystals and their origins were also discussed. The near-infrared emission bands seen at 820 nm and 978 nm can be attributed to the emission bands formed by the background Fe or other impurity-related defect complexes in Fe2+:ZnSe single crystals, rather than by doped transition-metal-related defects. With the increase in temperature, the PL intensity increased slightly and reached a maximum near room temperature for bound excitons (430–490 nm), but the PL intensity decreased significantly for impurity-defect emission bands (500–720 nm), indicating the occurrence of a thermal quenching effect. The excitation wavelength-dependent PL spectra showed that PL intensity first increased and then decreased with an increase in the excitation wavelengths, and the maximum PL intensity of the bound excitons was obtained at 364 nm. In addition, the X-ray photoelectron spectroscopy (XPS) results showed that both bivalent and trivalent iron ions were found, but bivalence was the dominant charge state for iron atoms in the iron-doped ZnSe single crystals, meaning that they are suitable for developing mid-infrared gain medium applications.

Achieving excitation wavelength-power-dependent colorful luminescence via multiplexing of dual lanthanides in fluorine oxide particles for multilevel anticounterfeiting.

The optical characteristics of multimode luminescent materials like multimode luminescence (photoluminescence, afterglow, thermoluminescence) and a multi-excitation source (light, thermal, mechanical force) play crucial roles in optical data storage and readout, document security and anticounterfeiting. A higher level of advanced anticounterfeiting may rely on multimode anticounterfeiting materials that can realize multicolor luminescence. Here, a highly integrated multimode and multicolor Y7O6F9:Er3+,Eu3+ material is developed through multiplexing of dual lanthanides in fluorine oxide particles. In photoluminescence and photoluminescence/up-conversion luminescence modes, the material Y7O6F9:Er3+,Eu3+ has the characteristic of excitation wavelength and power dependence. In the photoluminescence mode, under excitation at 254 nm and 365 nm, Y7O6F9:Er3+ and Y7O6F9:Eu3+ showed bright red and green emissions, respectively. In the photoluminescence/up-conversion mode, under the increased excitation power from 0.2 to 2.0 W cm-2, the color of luminescence emission can be finely tuned from red to orange, yellow and green. Taking this unique excitation wavelength-power-dependent luminescence property into account, a multilevel anticounterfeiting device with the Lily pattern was designed. The device readily integrates the advantages of the excitation wavelength-dependent photoluminescence emissions and excitation power-dependent photoluminescence emissions in one overall device. These findings offer unique insight for designing highly integrated multimode, multicolor luminescence materials and advanced anticounterfeiting technology toward a wide variety of applications, particularly multilevel anticounterfeiting devices.

Interfacial Grown Zinc Oxide Origami Structure for Broadband Visible Light Driven Photocatalysts

AbstractA novel route to synthesize large area ZnO/Zn(OH)2 origami thin films at air/liquid interface is reported. ZnO materials derived from this route show the largest blue‐shifted band‐to‐band emission at 3.85 eV (3.37 eV in bulk ZnO) so far, resulting from the quantum confinement in the ultrathin ZnO/Zn(OH)2 nanosheets. Interband defect levels (IDLs) related broadband photoluminescence is observed from UV to red region by excitation wavelength dependent photoluminescence measurements. The ZnO origami structures show photocatalytic methylene blue degradation (MB‐degradation) activity even under sub‐bandgap visible light illumination from 405 nm to green region at 505 nm, measured by low power monochromatic light emitting diode light sources. From the consistent light absorption, luminescence, and MB‐degradation activity, it can be concluded that the broadband visible light MB‐degradation activity is attributed to photogenerated carriers via IDLs. The 2D ZnO‐nanosheets in the origami structure better solve the dilemma of the IDLs in bulk materials, i.e., they are beneficial for light absorption in visible range but detrimental for enhanced recombination loss of carriers, and they can be quickly extracted to the surface without substantial recombination. This finding makes the ZnO origami a promising candidate for efficient photocatalyst that harvesting the sunlight and for indoor applications.

Excitation wavelength dependent photoluminescence and photochromic studies of Yb3+/Er3+ doped β−KYF4 and β−NaYF4 nanoparticles

We report both resonant and off-resonant laser excitation of Er3+ upconversion fluorescence and colour tunability in Er3+/Yb3+ co-doped KYF4 and NaYF4 nanoparticles. The nanoparticles were prepared using a hydrothermal method with particle sizes of 74 ± 20 nm and 345 ± 91 nm for β−KYF4 and β−NaYF4, respectively. The Yb3+ 2F7/2 → 2F5/2 absorption spectra exhibit absorption maxima at 10237 cm−1 (977 nm) for β−NaYF4 and 10267 cm−1 (974 nm) for β−KYF4 nanoparticles. The Er3+ upconversion fluorescence spectra consist of the 2H11/2,4S3/2, and 4F9/2 → 4I15/2 transitions for either 974, 977 or 980 nm laser excitation in both materials. We observed an enhancement in the upconversion intensity by a factor of up to 20 for β−KYF4 and 1.5 fold for β−NaYF4 under resonant excitation compared with off-resonant excitation at 980 nm. Tuneable upconversion fluorescence wavelength was achieved in β−KYF4:Yb/Er nanoparticles by adjusting the excitation wavelength. The CIE chromaticity coordinates are (0.6836, 0.3151) with a highest red colour purity of 99.70% for β−KYF4 (4700 K) and (0.3953, 0.5915) with a colour purity of 96.84% for β−NaYF4 (4533 K) nanoparticles. The respective absolute upconversion quantum yields are 1.18% and 2.34% under low power density (1.65 W⋅cm−2).

PH-Dependent Photophysical Properties of Metallic Phase MoSe2 Quantum Dots.

Fluorescence properties of quantum dots (QDs) are critically affected by their redox states, which is important for practical applications. In this study, we investigated the optical properties of MoSe2-metallic phase quantum-dots (MoSe2-mQDs) depending on the pH variation, in which the MoSe2-mQDs were dispersed in water with two sizes (Φ~3 nm and 12 nm). The larger MoSe2-mQDs exhibited a large red-shift and broadening of photoluminescence (PL) peak with a constant UV absorption spectra as varying the pH, while the smaller ones showed a small red-shift and peak broadening, but discrete absorption bands in the acidic solution. The excitation wavelength-dependent photoluminescence shows that the PL properties of smaller MoSe2-mQDs are more sensitive to the pH change compared to those of larger ones. From the time-resolved PL spectroscopy, the excitons dominantly decaying with an energy of ~3 eV in pH 2 clearly show the shift of PL peak to the lower energy (~2.6 eV) as the pH increases to 7 and 11 in the smaller MoSe2-mQDs. On the other hand, in the larger MoSe2-mQDs, the exciton decay is less sensitive to the redox states compared to those of the smaller ones. This result shows that the pH variation is more critical to the change of photophysical properties than the size effect in MoSe2-mQDs.

Voltage-controlled reversible modulation of colloidal quantum dot thin film photoluminescence

Active modulation of quantum dot thin film photoluminescence (PL) has been far-reaching potential applications in biomedical and optoelectronic systems, but challenges remain in achieving large PL modulation depth and fast temporal response. Here, we report an efficient voltage-controlled optical down-converter by optically exciting a colloidal quantum dot thin film within a quantum dot light-emitting diode under reverse bias. Utilizing field-induced luminescence quenching, we show that a large electric field can strongly modify carrier dynamics in this nanostructured device, resulting in stable and reversible photoluminescence quenching. The device exhibits photoluminescence reduction of up to 99.5%, corresponding to a contrast ratio of 200:1 under the applied electric field of 3 MV cm−1 with a 300 ns response time. Using excitation wavelength dependent and transient PL spectroscopy, we further show that the high degree of quenching is achieved by a synergistic interplay of quantum-confined Stark effect and field-induced exciton dissociation.

Excitation wavelength-dependent photoluminescence decay of single quantum dots near plasmonic gold nanoparticles.

Changing the excitation wavelength is a simple but effective strategy to modulate the photophysical cha racteristics of colloidal quantum dots (QDs) near plasmonic nanostructures. It has been observed that the photoluminescence (PL) decay of QDs near plasmonic nanostructures differs when the excitation wavelength is varied, but the exact mechanism is still unclear today. Here, we studied the excitation wavelength dependence of the PL decay of CdSe/CdS core/shell QDs near plasmonic gold nanoparticles at the single QD level. With the aid of statistical science, we demonstrated that the PL decay of a single QD near gold nanoparticles is generally faster when the QD is excited spectrally close to the localized surface plasmon resonance of gold nanoparticles. This excitation wavelength dependence is mainly caused by the varied proportion of photons coming from biexciton emission, which is the result of different local electric field enhancement by gold nanoparticles upon excitation.

Tunable upconversion emission from oil-based carbon nanodots

Optical properties of carbon dots (CDs), prepared using 10-Undeceonic acid as an organic precursor, exhibited broad range excitation wavelength-dependent photoluminescence, with maximum emission intensity at 3.5 eV. Besides conventional down-conversion PL (DCPL), CDs show excitation wavelength-dependent upconversion PL(UCPL), produced by electromagnetic radiation in the green-NIR wavelength range. The difference between the excitation energy and the UCPL peak energy is found to be constant upon varying the excitation energy, whereas the energy difference with respect to DCPL peak energy decreases linearly. UCPL/DCPL have been explained with the help of surface states, shallow and deep trap states present in the proposed CDs.

Label-Free Iron Oxide Nanoparticles as Multimodal Contrast Agents in Cells Using Multi-Photon and Magnetic Resonance Imaging.

IntroductionThe inherent fluorescence properties of iron oxide nanoparticles (IONPs) were characterized, and their applicability for multiphoton imaging in cells was tested in combination with their magnetic resonance imaging (MRI) capabilities.MethodsSuperparamagnetic iron oxide nanoparticles were synthesized and subsequently coated with polyethylene glycol to make them water-dispersible. Further characterization of the particles was performed using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), dynamic light scattering (DLS), superconducting quantum interference device (SQUID) and magnetic resonance relaxivity measurements. MRI and fluorescence properties of bare IONPs were first studied in solution and subsequently in A549-labeled cells.ResultsThe particles, with a core size of 11.3 ± 4.5 nm, showed a good negative MRI contrast in tissue-mimicking phantoms. In vitro studies in mammalian A549 cells demonstrate that these IONPs are biocompatible and can also produce significant T2/T2* contrast enhancement in IONPs-labeled cells. Furthermore, excitation-wavelength dependent photoluminescence was observed under one- and two-photon excitation.DiscussionThe obtained results indicated that IONPs could be used for fluorescence label-free bioimaging at multiple wavelengths, which was proven by multiphoton imaging of IONPs internalization in A549 cancer cells.

CdSe and CsPbBr3 quantum dot Co-doped monolithic glasses as tunable wavelength convertors

CdSe and CsPbBr3 quantum dots (QDs) are well studied photoluminescent materials due to their extraordinary emission properties. However, their vulnerability against environmental conditions limits their integration into further applications. At this point, glass encapsulation offers promising durability features due to its robust and dense structure. In this study, CdSe and CsPbBr3 QDs are successfully synthesized in the same glass host through the melt-quenching technique followed by a single heat-treatment process. Excitation wavelength dependent photoluminescence properties are investigated and emission color tunability of monolithic glasses from yellow-green to red is demonstrated. Favorable quantum yield values are obtained as 21.78% and 16.63% under 345 and 365 nm excitation wavelengths, respectively. The prepared glasses demonstrate high potential to be used as tunable wavelength convertors for state-of-the-art photonic and opto-electronic applications.

Nitrogen, boron-doped Ti3C2 MXene quantum dot-based ratiometric fluorescence sensing platform for point-of-care testing of tetracycline using an enhanced antenna effect by Eu3.

The Ti3C2 MXene quantum dots (Ti3C2 MQDs) derived from Ti3C2 MXene have received much attention because of their remarkable advantages in biosensing. Nevertheless, the functionalization of Ti3C2 MQDs to improve their properties is just in its infant stage. Herein, we firstly synthesized nitrogen and boron co-doped Ti3C2 MQDs (N, B-Ti3C2 MQDs) with good water solubility, strong stability, and high optical characteristics. The N, B-Ti3C2 MQDs exhibit excitation wavelength-dependent blue photoluminescence with optimal excitation/emission peaks at 335/439nm. Nowadays, the development of fast and real-time detection of tetracycline (TC) in animal derived food is very essential. In this work, a novel point-of-care testing (POCT) platform was established based on ratiometric fluorescence method using N, B-Ti3C2 MQDs coupled with Eu3+. Upon addition of TC in the Eu3+/N, B-MQDs system, blue fluorescence emission of N, B-Ti3C2 MQDs was quenched and red fluorescence emission of Eu3+ was enhanced gradually, which was ascribed to the synergistic inner filter effect and antenna effect. Moreover, we prepared test papers with N, B-Ti3C2 MQDs and Eu3+ for TC detection based on the change of fluorescence color, which could be recognized by color recognizer app installed in the smartphone. Therefore, great promise for POCT of TC is givenwith the merits of simplicityand visible detection possibility.The proposed method demonstrated a low detection limit of 20nM. Applicationof the platform for TC quantification in milk samples opened a novel means for the potential use ofN, B-Ti3C2 MQDs in food safety.

Role of Trap States in Excitation Wavelength-Dependent Photoluminescence of Strongly Quantum-Confined All-Inorganic CsPbBr3 Perovskites with Varying Dimensionalities

Role of Trap States in Excitation Wavelength-Dependent Photoluminescence of Strongly Quantum-Confined All-Inorganic CsPbBr₃ Perovskites with Varying Dimensionalities

Towards Red Emissive Systems Based on Carbon Dots.

Carbon dots (C-dots) represent an emerging class of nontoxic nanoemitters that show excitation wavelength-dependent photoluminescence (PL) with high quantum yield (QY) and minimal photobleaching. The vast majority of studies focus on C-dots that exhibit the strongest PL emissions in the blue/green region of the spectrum, while longer wavelength emissions are ideal for applications such as bioimaging, photothermal and photodynamic therapy and light-emitting diodes. Effective strategies to modulate the PL emission of C-dot-based systems towards the red end of the spectrum rely on extensive conjugation of sp2 domains, heteroatom doping, solvatochromism, surface functionalization and passivation. Those approaches are systematically presented in this review, while emphasis is given on important applications of red-emissive suspensions, nanopowders and polymer nanocomposites.

Atypical Green Luminescence from Raw Cassia Siamea Extract: A Comparison with Red Emitting Tinospora Cordifolia.

Optical and electrochemical properties from Cassia and Giloy leaves' raw extract have been studied, and they show similar properties as UV absorber but different emission properties, under UV excitation, even though they appear the same in natural light. Giloy and Cassia extracts show red and green luminescence, respectively, under UV excitation. Like the appearance, their redox properties are also similar, which shows that both can act as antioxidants. Raman spectroscopy and excitation wavelength dependent photoluminescence data have been compared. The difference in relative emission intensities have been explained based on the presence of corresponding color centers in different ratios in the two leaves.

Orange Photoluminescence from Hydrothermally Grown Zno Nanorods and Study on its Defects

The visible photoluminescence (PL) of ZnO is controversial for a long time. At present, the contribution of oxygen interstitial defects to yellow/orange emission from ZnO nanostructures is on debate. In this report, the origin of orange emission from solution- grown ZnO nanorods is investigated using excitation wavelength dependent photoluminescence PL, PL excitation and UV-Vis spectra. These results showed that orange emission may be due to the transition of an electron from shallow defect levels positioned slightly below the conduction band to the singly ionized oxygen vacancies. Hence, it is believed that oxygen interstitials may not be responsible for orange emission from solution grown ZnO nanostructures.