Strong Photoluminescence Intensity Research Articles

Strain and optical characteristics analyses of three-dimentional self-ordered multilayered SiGe nanodots by photoluminescence and Raman spectroscopy

The strain state, optical properties, and band structure of the self-ordered multilayered silicon-germanium (SiGe) nanodots, which are staggered and dot-on-dot alignment and embedded by Si spacer, were evaluated by Raman spectroscopy and low-temperature photoluminescence (PL). These results suggest that the compressive strain applied to the staggered nanodots is smaller than that of the dot-on-dot nanodots, which contributes to the shrinking of the bandgap of the staggered nanodots. Strong PL intensity was observed from the nanodots compared to the single crystalline bulk SiGe due to the carrier confinement and high crystal quality of the nanodots. The stack-controlled nanodots showed a redshift of the PL peaks compared to the bulk SiGe and the effect of strain induced in SiGe nanodots might not be enough to explain this phenomenon. The cause of the redshift was clarified by considering the hetero band structure of the nanodots and the tensile strained spacer.

Chirality-Regulated Clusteroluminescence in Polypeptides.

The low emission efficiency of clusteroluminogens restricts their practical applications in the fields of sensors and biological imaging. In this work, the clusteroluminescence of ordered/disordered polypeptides was observed, and the photoluminescence (PL) intensity of polypeptides can be modulated by the chirality of amino acid residues. Polyglutamates with different chiral compositions were synthesized, and the racemic polypeptides exhibited a significantly higher PL intensity than the enantiopure ones. This emission originates from the n-π* transition between C═O groups of polypeptides and is enhanced by clusterization of polypeptides. CD and Fourier transform infrared spectra demonstrated that the enantiopure and racemic polypeptides form α-helix and random coil structures, respectively. The disordered polypeptides can form more chain entanglements and interchain interactions because of their high flexibility, leading to more clusterizations and stronger PL intensity. The rigidity of ordered helical structures restrains the chain entanglements, and the formation of intrachain hydrogen bonds between amide groups of the backbone impairs the interchain interaction between polypeptides, resulting in lower PL intensity. The PL intensity of the polypeptides can also be manipulated by the addition of urea or trifluoroacetic acid. Our study not only elucidates the chirality/order-based structure-property relationship of clusteroluminescence in peptide-based polymers but also offers implications for the rational design of fluorescent peptides/proteins.

Optimization of visible photoluminescence emission from Ni-Zn ferrite thin films

Ni-Zn ferrite films with different thicknesses were prepared by the spray method, aiming to study the relationship between the annealing effect in an oxygen rich environment and the structural, optical properties and photoluminescence emission. X-ray diffraction (XRD) analysis used with Rietveld refinement showed that all prepared samples had a single spinel phase structure. Likewise, the Fourier transform infrared (FTIR) spectra confirmed the phase formation of Ni-Zn ferrites by appearing in both of the two characteristic absorption bands which are related to the tetrahedral and octahedral sites. For annealed thin film samples of Ni-Zn ferrite, the atomic force microscope (AFM) surface morphology exhibits pinning structure on the surface in nanoscale height, whereas for un-annealed samples, there are hills and valleys cover a broad region. The different electronic transitions were estimated from the UV-visible transmission spectrum. Strong photoluminescence (PL) intensity in the visible range was observed under the excitation of UV radiation. The intensity of the PL signal was strongest at a film thickness of 750 nm then decreased for higher thicknesses. This could be interpreted by using proposed energy level structures based on the transmission spectrum of the investigated samples. The strong PL intensity introduces the samples as a direct optical detector for UV radiation.

Observation of Strong Anisotropic Interlayer Excitons.

Anisotropic interlayer excitons had been theoretically predicted to exist in two-dimensional (2D) anisotropy/isotropy van der Waals heterojunctions. However, experimental results consolidating the theoretical prediction and exploring the related anisotropic optoelectronic response have not been reported so far. Herein, strong photoluminescence (PL) of anisotropic interlayer excitons is observed in a symmetric anisotropy/isotropy/anisotropy heterojunction exemplified by 3L-ReS2/1L-MoS2/3L-ReS2 using monolayer (1L) MoS2 and trilayer (3L) ReS2 as components. Sharp interlayer exciton PL peaks centered at ∼1.64, ∼1.61, and ∼1.57 eV are only observed at low temperatures of ≤120 K and become more pronounced as the temperature decreases. These interlayer excitons exhibit strong anisotropic PL intensity variations with periodicities of 180° as functions of the incident laser polarization angles. The polarization ratios of these interlayer excitons are calculated to be 1.33-1.45. Our study gives new insight into the manipulation of excitons in 2D materials and paves a new way for a rational design of novel anisotropic optoelectronic devices.

L-tyrosine capped silver nanocluster: An efficient reusable luminescent nano-probe for simple, rapid and reliable detection of hemoglobin in real blood samples

Easy and rapid quantification of hemoglobin (Hb) in the human body is essential for early screening of hematological disorders like anemia. Herein, we synthesized atomically precise tyrosine-protected photoluminescent silver nanocluster (Tyr-Ag NC) in a facile one-pot method. The synthesized nanocluster showed strong photoluminescence (PL) intensity peaked at 410 nm that can be selectively turned off by Hb with utmost sensitivity (limit of detection = 30 pM), thereby making the nanocluster a promising nano-probe for the detection of Hb. The observed PL quenching can be attributed to a complexation followed by a static charge transfer transition between the nanocluster and hemin, the cofactor of Hb involving both Fe2+ and the porphyrin ligand. The Fe2+ plays a key role in the complex formation which was disrupted by the formation of hydroxyl radicals through the Fe2+-H2O2 mediated Fenton reaction, restoring the PL intensity of the Tyr-Ag NC, ensuring its reusability for the detection of Hb. Compared to the conventional clinical techniques involving toxic chemicals and/or expensive equipment, the synthesized Tyr-Ag NC allows quick, direct, easy, accurate and cost-effective detection and quantification of Hb in real human serum and blood samples suggesting its tremendous practical applications for healthcare assessment.

The development and applications of nanoporous gallium nitride in optoelectronics: a review

The development of nanoporous gallium nitride (NP-GaN) has widened the material properties and applications in third-generation semiconductor areas. NP-GaN has been used in laser emitters, light-emitting diodes, optical sensors, and optical energy storage devices. In this paper, we reviewed the most recent progress in the NP-GaN field by electrochemical etching. The etched GaN has many superior properties compared with original GaN templates, such as stronger photoluminescence intensity, thermal conductivity, piezo-electricity, more accessible area, stress relief, and refractive index. These advantages will make GaN more widely used in the field of optics and optoelectronics. Pore formation can be controlled by adjusting the applied potential and etching time. The NP-GaN makes the material of GaN have broader application prospects. We introduced in detail the application prospects of different GaN based processes and subsequent application methods in optoelectronics, sensors, and materials themselves. This review will help to improve further development of NP-GaN applications.

Rapid Detection of Ag(I) via Size-Induced Photoluminescence Quenching of Biocompatible Green-Emitting, l-Tryptophan-Scaffolded Copper Nanoclusters.

Atomically precise metal nanoclusters capped with small molecules like amino acids are highly favored due to their specific interactions and easy incorporation into biological systems. However, they are rarely explored due to the challenge of surface functionalization of nanoclusters with small molecules. Herein, we report the synthesis of a green-emitting (λex = 380 nm, λem = 500 nm), single-amino-acid (l-tryptophan)-scaffolded copper nanocluster (Trp-Cu NC) via a one-pot route under mild reaction conditions. The synthesized nanocluster can be used for the rapid detection of a heavy metal, silver (Ag(I)), in the nanomolar concentration range in real environmental and biological samples. The strong green photoluminescence intensity of the nanocluster quenched significantly upon the addition of Ag(I) due to the formation of bigger nanoparticles, thereby losing its energy quantization. A notable color change from light yellow to reddish-brown can also be observed in the presence of Ag(I), allowing its visual colorimetric detection. Portable paper strips fabricated with the Trp-Cu NC can be reliably used for on-site visual detection of Ag(I) in the micromolar concentration range. The Trp-Cu NC possesses excellent biocompatibility, making it a suitable nanoprobe for cell imaging; thus, it can act as an in vivo biomarker. The nanocluster showed a significant spectral overlap with anticancer drug doxorubicin and thus can be used as an effective fluorescence resonance energy transfer (FRET) pair. FRET results can reveal important information regarding the attachment of the drug to the nanocluster and hence its role as a potential drug carrier for targeted drug delivery within the human body.

Highly Sensitive Immunochromatographic Detection of Zearalenone Based on Ultrabright Red-Emitted Aggregation-Induced Luminescence Nanoprobes.

Highly luminescent nanospheres have been demonstrated in enhancing the sensitivity of lateral flow immunoassay (LFIA) due to their loading numerous luminescent dyes. However, the photoluminescence intensities of existing luminescent nanospheres are limited due to the aggregation-caused quenching effect. Herein, highly luminescent aggregation-induced emission luminogens embedded nanospheres (AIENPs) with red emission were introduced as signal amplification probes of LFIA for quantitative detection of zearalenone (ZEN). Optical properties of red-emitted AIENPs were compared with time-resolved dye-embedded nanoparticles (TRNPs). Results showed that red-emitted AIENPs have stronger photoluminescence intensity on the nitrocellulose membrane and superior environmental tolerance. Additionally, we benchmarked the performance of AIENP-LFIA against TRNP-LFIA using the same set of antibodies, materials, and strip readers. Results showed that AIENP-LFIA exhibits good dynamic linearity with the ZEN concentration from 0.195 to 6.25 ng/mL, with half competitive inhibitory concentration (IC50) and detection of limit (LOD) at 0.78 and 0.11 ng/mL, respectively. The IC50 and LOD are 2.07- and 2.36-fold lower than those of TRNP-LFIA. Encouragingly, the precision, accuracy, specificity, practicality, and reliability of this AIENP-LFIA for ZEN quantitation were further characterized. The results verified that the AIENP-LFIA has good practicability for the rapid, sensitive, specific, and accurate quantitative detection of ZEN in corn samples.

Relationship between epi-wafer photoluminescence and focal plane array performances of InGaAs detectors

The relationship between photoluminescence properties of InGaAs detector epi-wafers and the performances of focal plane arrays has been established according to the measurements of various samples. The average signal, dark signal and noise of the fabricated focal plane arrays were characterized and correlated to the photoluminescence intensities and nonuniformities of the epi-wafers. The average response signal is increased as the increased photoluminescence. The signal nonuniformity and dark signal are markedly related to nonuniformity of photoluminescence intensity, while the noise voltages are not correlated to photoluminescence results. The microwave photoconductance decay measurements reveal that the epi-wafers with stronger photoluminescence intensity has longer minority carrier lifetime. This work supplies a feasible pathway to evaluate and predict the performances of focal plane arrays fabricated by InGaAs detector epi-wafers before device processing.

Lysozyme protected copper nano-cluster: A photo-switch for the selective sensing of Fe2+

Protein capped metal nanoclusters gained a lot of recent attention due to their wide range of applications. However copper nanoclusters are difficult to synthesize due to their tendency to undergo oxidation. Here we successfully synthesized a stable, biocompatible lysozyme protected Cu nanocluster (Lys-Cu NC) using an optimized green one-pot protocol under aqueous condition at room temperature. The nanocluster showed a strong photoluminescence intensity (λex = 365 nm, λem = 430 nm) which can be significantly and selectively quenched (off) by Fe2+ ions. Upon addition of NaOH the initial photoluminescence intensity can be recovered completely (on) thereby making the nanocluster a suitable candidate for a photo switch that can be reliably reused for the selective and sensitive detection of Fe2+ ions in the nanomolar (detection limit ∼ 2.5 nM) concentration range. The synthesized nanocluster further has been successfully used to rapidly estimate iron level in complex systems such as ground water and human hemoglobin samples. The photoluminescence intensity of the nanocluster is also sensitive towards temperature indicating that it can be used as a temperature sensor in different biological systems. The nanocluster further used as an excellent nanoprobe for in-vivo cell imaging studies. Thus this Lys-Cu NC can be emerged as a next generation novel nanoprobe for various interdisciplinary applications.

Silicon nanocrystal synthesis with the atmospheric plasma source HelixJet

AbstractThe HelixJet, a plasma source operating under atmospheric pressure with RF power, was used for the synthesis of silicon nanoparticles (Si‐NPs) in the context of relevance in nanomedicine, sensor technology, and nanotechnology. The HelixJet was operated with a variety of He/Ar/H2/SiH4 gas mixtures to characterize the Si‐NPs in regard to their size, crystallinity, structure, and photoluminescence. Distinct varieties of nanomaterials in the size range from 3 nm to over 100 nm were synthesized depending on the operation parameters of the HelixJet. Admixture of H2 alongside high RF powers led to the formation of crystalline nanoparticles with a strong photoluminescence intensity, where the photoluminescence properties as well as the nanocrystal synthesis yield were tunable by adjustment of the synthesis parameters. Post‐synthesis in‐flight annealing allowed the formation of large crystalline nanoparticles. In addition, the experiments conducted in this study resulted in a design improvement of the HelixJet plasma source that extends the stability of the operating range. Furthermore, the added spatial separation of the He/H2 and He/Ar/SiH4 streams (SiH4 injection on‐axis) minimizes material deposition within the HelixJet and enables continuous long‐term operation.

(Digital Presentation) Fabrication of Thick SiGe／Ge Multiple Quantum Wells on Ge-on-Si and Their Optical Properties

We fabricate thick strained Si0.1Ge0.9/Ge multiple quantum wells (MQWs) structures on Ge-on-Si, and evaluate their crystallinities and optical properties. As a result, it is found that highly crystalline Si0.1Ge0.9/Ge MQWs are grown both on Ge-on-Si(100) or Ge-on- Si(111), where surface roughness slightly differs between the two. From both MWQs we obtain strong room-temperature photoluminescence (PL) via quantum confinements of carriers in the MQWs. It is also found that the PL peak positions and intensities are different between (100) and (111). Surface roughening is considered to cause reduction in the PL intensity and the peak shift for the (111) case whereas the MQWs on Ge-on-Si(100) shows very smooth surface and resultantly strong PL intensity, indicating that Si0.1Ge0.9/Ge MQWs are promising for applications to light-emitting devices that can be integrated on the Si platform.

Synthesis and effects of co-dopants (La3+ , Sm3+ , Mn2+ , Nd3+ , V5+ , Y3+ ) on photoluminescence of SrAl2 O4 :Dy3+ phosphor.

In this research, the co-dopant effects on photoluminescence (PL) properties of SrAl2 O4 :Dy3+ phosphors were studied. The phosphor powders were prepared with solid state reaction, which is the method that is frequently preferred in SrAl2 O4 phosphors and efficient results are obtained in terms of PL properties. X-ray diffraction (XRD) patterns of all co-doped samples were fitted with pdf card#01-034-0379. Fourier-transform infrared (FTIR) analysis supports the phase evolution determined in the XRD results. PL examinations started with the SrAl2 O4 that was synthesized with the addition of boron, and then continued with the doped/and co-doped samples. Except for the Sm3+ co-doped phosphor, PL data of characteristic Dy3+ transitions were obtained for other lanthanide and metal ion co-dopants. The strongest PL intensity was demonstrated in the SrAl2 O4 :Dy3+ ,V5+ . SrAl2 O4 :Dy3+ ,Sm3+ phosphor shows both the Dy3+ and Sm3+ ions transition related peaks appeared in the same spectrum. In the continuation of the studies, SrAl2 O4 :Dy3+ ,Sm3+ and SrAl2 O4 :Dy3+ ,V5+ powders were immersed in water for 2 h. Regardless of the presence of Dy3+ luminescent centers and other co-dopants, broadband and intense blue emission peak at 445 nm was recorded which is directly related to newly formed phases by the decomposition of SrAl2 O4 .

Boosted Charge‐Carrier Transport in Triple‐Cation Perovskites by Ultrasonic Vibration Post Treatment

AbstractUltrasonic vibration imposed on the substrate of a drying perovskite solution film has previously been proposed as a nearly annealing‐free method to improve film quality and thus the photovoltaic performance for perovskite solar cells. However, an in‐depth understanding of the underlying mechanism of the improved film quality via ultrasonic vibration is still lacking. In this work, the effects of substrate vibration post treatment on the carrier lifetime and mobility are studied in triple‐cation perovskite films. With 80 s of annealing‐free vibration, the perovskite film demonstrates much stronger photoluminescence intensity and much longer carrier lifetime up to 2.634 µs, 2 orders of magnitude longer than that of the thermal annealed films. Optical pump terahertz probe spectroscopy reveals that the charge‐carrier mobility increases to 121 ± 44 cm2 V−1 s−1 when subjected to 80 s vibration followed by annealing. Such mobility is about 80 ± 40 cm2 V−1 s−1 higher than that of other polycrystalline organic–inorganic hybrid perovskite thin films of similar composition. The diffusion length is improved to nearly 1.5 times. The new understanding on the vibration‐induced charge‐carrier transport properties paves the way for the application of ultrasonic vibration toward the performance improvement of perovskite‐based electronic devices.

Marked Efficiency Improvement of FAPb0.7Sn0.3Br3 Perovskite Light-Emitting Diodes by Optimization of the Light-Emitting Layer and Hole-Transport Layer.

Highly luminescent FAPb0.7Sn0.3Br3 nanocrystals with an average photoluminescence (PL) quantum yield of 92% were synthesized by the ligand-assisted reprecipitation method. The 41-nm-thick perovskite film with a smooth surface and strong PL intensity was proven to be a suitable luminescent layer for perovskite light-emitting diodes (PeLEDs). Electrical tests indicate that the double hole-transport layers (HTLs) played an important role in improving the electrical-to-optical conversion efficiency of PeLEDs due to their cascade-like level alignment. The PeLED based on poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,40-(N-(p-butylphenyl))-diphenylamine)] (TFB)/poly(9-vinylcarbazole) (PVK) double HTLs produced a high external quantum efficiency (EQE) of 9%, which was improved by approximately 10.9 and 5.14 times when compared with single HTL PVK or the TFB device, respectively. The enhancement of the hole transmission capacity by TFB/PVK double HTLs was confirmed by the hole-only device and was responsible for the dramatic EQE improvement.

Structure, morphology and optical characterization of Sm3+-doped MgGeO3 nanocrystals for warm white light emitting devices

Orange-red emitting Sm[Formula: see text]-doped MgGeO3 phosphors were synthesized by traditional high temperature solid state method. The powders were characterized by using X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), UV-Vis spectrometer and photoluminescence (PL) spectra. XRD, SEM and EDS analysis results revealed that MGO:Sm phosphor samples were successfully synthesized. and the optimum MGO:0.1% mol Sm[Formula: see text] phosphor exhibited good photoluminescence emission intensity, thermal stability, life time and color purity. The diffuse reflectance spectra give the results of sample absorption, reflectance, transmittance and optical band gap. The larger optical band gap is 5.25 eV and the stronger photoluminescence intensity [Formula: see text] when the doping concentration is 0.1[Formula: see text] mol. The dipole–dipole interaction is the main mechanism of the concentration quenching phenomenon. The thermal activation energy of the sample is 0.176 eV, and the life time of the prepared sample can reach 14.76 [Formula: see text]s, due to the correlated color temperature (CCT) of less than 2000 K, the potential application value in warm white light emitting device.

Synthesis and Comparison of Eu3+ Doped M-Gd2(MoO4)3 and O-Gd2(MoO4)3 Phosphors

The Eu3+ doped monoclinic phase of Gd2(MoO4)3 (M-Gd2(MoO4)3) and the Eu3+ doped orthorhombic phase of Gd2(MoO4)3 (O-Gd2(MoO4)3) red phosphors were synthesized by adjusting the synthesis temperatures. The XRD (X-ray diffraction) patterns, the EDS (energy-dispersive spectra), and the FE-SEM (field emission scanning electron microscope) images were used to comparatively study crystalline structures, compositions, and morphologies of the two materials. The DRS (diffuse reflection spectra), the room and high temperature PL (photoluminescence) spectra, and the fluorescence decay curves were recorded to compare the PL properties of the two phosphors. The characterization results suggest that the M-Gd2(MoO4)3 phosphor has lower synthesis temperature, while the O-Gd2(MoO4)3 phosphor has bigger particles, larger energy band gap value, stronger PL intensities, longer lifetimes, and better thermal stabilities. For Eu3+, the research results prove that the O-Gd2(MoO4)3 is a better host material choice than that of the M-Gd2(MoO4)3.

Luminescence Properties of InGaN/GaN Green Light-Emitting Diodes with Si-Doped Graded Short-Period Superlattice.

The optical properties of InGaN/GaN green light-emitting diodes (LEDs) with an undoped graded short-period superlattice (GSL) and a Si-doped GSL (SiGSL) were investigated using photoluminescence (PL) and time-resolved PL spectroscopies. For comparison, an InGaN/GaN conventional LED (CLED) without the GSL structure was also grown. The SiGSL sample showed the strongest PL intensity and the largest PL peak energy because of band-filling effect and weakened quantum- confined stark effect (QCSE). PL decay time of SiGSL sample at 10 K was shorter than those of the CLED and GSL samples. This finding was attributed to the oscillator strength enhancement by the reduced QCSE due to the Coulomb screening by Si donors. In addition, the SiGSL sample exhibited the longest decay time at 300 K, which was ascribed to the reduced defect and dislocation density. These results indicate that insertion of the Si-doped GSL structure is an effective strategy for improving the optical properties in InGaN/GaN green LEDs.

Effect of reaction time and different solvents ratios on the formed phases and optical properties of formamidinium lead bromide

Formamidinium lead bromide (FAPbBr3) thin films were prepared using two different solvents (N, N-Dimethylformamide, DMF and Methyl sulfoxide, MSO) with different ratios (1 DMF: 4 MSO and 4 DMF: 1 MSO) and different reaction times (4 h and 24 h). The effect of different solvents ratios and reaction time on the crystallinity and different phases percentage was examined using x-ray diffraction technique. Also, the influence on the transmittance, reflectance, absorbance coefficient, refractive index, extinction coefficient, real and imaginary parts of the dielectric constant and optical conductivity for FAPbBr3 thin films was explored using UV–vis spectrophotometer. All films showed interference, which verifies the high crystallinity of the films as confirmed from XRD data. The refractive index exhibited multi-oscillating peaks. The optical band gap energy for the FAPbBr3 perovskite thin films changed slightly either with varying the ratio between the solvents used in the preparation or the reaction time. FAPbBr3 thin films prepared with 1 DMF: 4 MSO are excellent nonlinear optical materials. FAPbBr3 perovskite thin films prepared with 1 DMF: 4 MSO exhibited the strong photoluminescence intensity and narrow full width at half maximum intensity.

Great enhancement on two-photon photoluminescence imaging contrast of Au nanoparticles via double-pulse femtosecond laser excitation with controlled phase differences.

Au nanoparticles are attractive contrast agents for noninvasive living tissue imaging with deep penetration because of their strong two-photon photoluminescence (TPPL) intensity and excellent biocompatibility. However, the inevitable phototoxicity and huge auto-fluorescence are consistently associated with laser excitation. Therefore, enhancement of TPPL intensity and suppression of backgrounds are always highly desired under the demand of reducing excitation powers. In this work, we develop a double-pulse TPPL (DP-TPPL) scheme with controlled phase differences (Δφ) between the double pulses to significantly improve the signal-to-noise ratio (SNR) of TPPL imaging. Under the modulated phase (Δφ periodically varying between 0-2π), our results show that SNR can be improved from 4.3 to 1715, with an enhancement of up to 400 folds at the integration of 50 ms. More importantly, this enhancement can be unlimitedly lifted by increasing the number of photons or integration times in principle. Further boosting has been achieved by reducing the magnitude of background noises; subsequently, SNR is improved by more than 104 times. Our schemes offer great potential for reducing phototoxicity and extracting extremely weak signals from huge backgrounds and open up a new possibility for a rapid, flexible, and reliable medical diagnosis by TPPL imaging with diminished laser powers.