Maximum Wavelength Research Articles

Theoretical study of the influence of electron push or pull bipyridine ligands on the electronic structure of Eu3+ ibuprofenate complexes

In this work, we showed the influence of dissubstituted bipyridine ligands with electron push or pull groups in the structural and electronic properties of the Eu3+ ibuprofenate complexes. QTAIM-DFT analyzes performed for the sixteen complexes demonstrated that the interaction between the 6,6′-X-bpy ligands and the Eu3+ ion is strongly weakened when X = –OCH3 (complex 10) and –NO2 (complex 16) due to steric hindrances and a decrease in ligand basicity. The Gibbs free energy of the formation of these complexes is less favored around 27 kcal mol−1 compared to complex 3 (X = 5,5′-NH2-bpy), which is the most thermodynamically stable structure. The calculated absorption bands in the ultraviolet region revealed that bpy ligands containing strongly electron donating groups shift the maximum absorption wavelength towards the near visible region. These results suggest that the studied Ln3+ ion complexes may be used in molecular devices with optoelectronic applications in the visible region.

Photocatalytic desulfurization of gas condensate using zinc diacetate and cadmium diacetate liquid catalysts

This inquiry studied the application of photocatalytic desulfurization as an effective method for removing sulfur-containing organic compounds from gas condensate extracted from oil wells. To this end, cadmium diacetate and zinc diacetate compounds were prepared as the liquid catalysts. Then their structures were confirmed and their properties were determined by common methods, including FTIR, NMR, and UV. Subsequently, their performances as catalysts were investigated by an optical technique for the desulfurization process. Accordingly, the study used a photoreactor equipped with a 250 W mercury ultraviolet lamp with a maximum wavelength of 365 nm, and investigated and optimized the effect of the ratios of the influencing parameters on the total sulfur removal efficiency. These included the ratios of fuel to photocatalyst, H2O2, and acetonitrile. Ratios of 1:2:3:2 and 1:3:2:1 (fuel: catalyst: oxidant: solvent) of zinc and cadmium diacetate led to 93.5 % and 87.1 % reduction of the total sulfur content, respectively, after 60 min since the exposure process. Also, under sunlight, the total sulfur removal was 67.0 % for the Zn diacetate and 42.0 % for Cd diacetate. Liquid diacetate photocatalysts were successfully recycled over five cycles with only a maximum of 10 % reduction in efficiency. The kinetics of the systems studied were evaluated under optimal conditions and it was found that both systems fit the pseudo-first order model with rate constants of 0.148 min−1 and 0.098 min−1, respectively. In the final step, some physicochemical properties of the desulfurized sample crucial in evaluation of fuel quality were determined under optimal conditions and compared with the properties of the original sample. The results indicated that the liquid photocatalysts used in the experiment increased the quality of the fuel by changing its important indicators by reducing its freezing point in addition to increasing its cetane number.

Determination of N-Acetyl-L-cysteine Ethyl Ester (NACET) by Sequential Injection Analysis.

New sequential injection analysis (SIA) methods with optical sensing for the determination of N-acetyl-L-cysteine ethyl ester (NACET) have been developed and optimized. NACET is a potential drug and antioxidant with advantageous pharmacokinetics. The methods involve the reduction of Cu(II) in its complexes with neocuproine (NCN), bicinchoninic acid (BCA), and bathocuproine disulfonic acid (BCS) to the corresponding chromophoric Cu(I) complexes by the analyte. The absorbance of the Cu(I) complexes with NCN, BCA, and BCS was measured at their maximum absorbance wavelengths of 458, 562, and 483 nm, respectively. The sensing manifold parameters and experimental conditions were optimized for each of the Cu(II) complexes used. Under optimal conditions, the corresponding linear calibration ranges, limits of detection, and sampling rates were 8.0 × 10-6-2.0 × 10-4 mol L-1, 5.5 × 10-6 mol L-1, and 60 h-1 for NCN; 6.0 × 10-6-1.0 × 10-4 mol L-1, 5.2 × 10-6 mol L-1, and 60 h-1 for BCA; and 4.0 × 10-6-1.0 × 10-4 mol L-1, 2.6 × 10-6 mol L-1, and 78 h-1 for BCS. The Cu(II)-BCS complex was found to be best performing in terms of sensitivity and sampling rate. Usual excipients in pharmaceutical preparations did not interfere with NACET analysis.

Selective fluorescence detection of acetylsalicylic acid, succinic acid and ascorbic acid based on a responsive lanthanide metal fluorescent coordination polymer.

A fluorescent sensor for highly selective and ultrasensitive detection of acetylsalicylic acid (ASA), succinic acid (SA), and ascorbic acid (AA) was reported. The water-soluble fluorescent ligand salicylic acid (Sal) was generated through catalyzing ASA by the hydrolase activity of zeolitic-imidazolate framework-8 (ZIF-8) or natural esterase (Est). The Sal can coordinate with 2-methylimidazole (2-MIm) and Ln(III) to form a fluorescent lanthanide coordination polymer (LCP), which has a fluorescence emission peak with the maximum wavelength at 412 nm (the excitation wavelength at 300 nm). Therefore, the detection of ASA can be achieved through the fluorescence intensity changes of LCPs in the system, which has comparable sensitivity and good selectivity (linear range of 0.031-1.00 mM and LODs of 11.72 and 3.22 μM) as compared to a direct reaction between Est/ZIF-8 and ASA for detecting ASA (linear range of 0.05-1.20 mM and limits of detection (LODs) of 4.43 and 4.58 μM). Furthermore, upon the addition of SA and AA, the fluorescence intensity of the reaction system can be enhanced and weakened through changing the energy resonance transfer pathways and affecting the enzymatic reaction process, respectively, realizing their sensitive and selective fluorescence detection. The established fluorescent sensors can work well in a wide linear range of SA concentrations from 0 to 2.50 mM (Est-based reaction system) and 0 to 1.50 mM (ZIF-8-based reaction system) with the LODs of 0.032 and 0.028 mM, respectively. The linear ranges of AA concentrations are from 0.0078 to 0.25 mM (Est-based reaction system) and 0.0078 to 0.13 mM (ZIF-8-based reaction system) with the LODs of 2.54 and 3.80 μM, respectively. The established sensors were successfully used in the detection of SA in rabbit plasma, with a recovery of 84.0%-98.7%. Additionally, the contents of ASA in Aspirin Enteric-Coated tablets and AA in vitamin C tablets were also determined by the developed methods.

Halotolerant Bacteria from Genus Nesterenkonia sandarakina VSA9 as a Potential Polyhydroxyalkanoate Producer.

Nesterenkonia sandarakina VSA9 pigmented bacteria isolated from Sargassum is being reported to produce polyhydroxyalkanoates (PHA) deduced through detecting the presence of pha C gene using the molecular method. The PHA synthase gene was of type I which has been concluded from the phylogenetic tree and multiple sequence analysis. The amino acid analysis of pha C gene confirms the involvement of the lipase box having a sequence of G-Y-C-I-G-G with cysteine as the active center of the PHA synthase. Homology modeling predicted the 3D protein structure which is similar to the PHA synthase of Chromobacterium sp. USM2. The solvent extract of N. sandarakina VSA9 showed the presence of Carotenoid compound with maximum wavelength at 475nm. The study's findings could have far-reaching implications, contributing to advancements in the biotechnology, industrial processes, and sustainable practices. The simultaneous production of carotenoids and PHAs by N. sandarakina VSA9 presents exciting opportunities for the development of innovative and environmentally friendly applications.

Silver nanoparticles (NPAg) using padina australis seaweed

The synthesis of silver nanoparticles (NPAg) using Padina australis seaweed as a bioreductor and AgNO₃ as a precursor through the green synthesis method was successfully achieved. This environmentally friendly approach utilized various concentrations of the seaweed extract and silver nitrate precursor, resulting in the formation of silver nanoparticles at each concentration variation. The stability of these nanoparticles was confirmed by the observable changes in solution color, maximum wavelength, absorbance, and peak length shift. The process exhibited consistent results, with minimal wavelength variation occurring within 1 to 6 hours, particularly at a concentration ratio of 3 mM and 5:10 mL extract to precursor. These findings demonstrate the potential of Padina australis seaweed in the sustainable production of silver nanoparticles, offering a green alternative for nanoparticle synthesis.

A Novel Plasmonic Sensor Based on Dual-Channel D-Shaped Photonic Crystal Fiber for Enhanced Sensitivity in Simultaneous Detection of Different Analytes.

A dual-channel D-shaped photonic crystal fiber (PCF) based plasmonic sensor is proposed in this paper for the simultaneous detection of two different analytes using the surface plasmon resonance (SPR) technique. The sensor employs a 50 nm-thick layer of chemically stable gold on both cleaved surfaces of the PCF to induce the SPR effect. This configuration offers superior sensitivity and rapid response, making it highly effective for sensing applications. Numerical investigations are conducted using the finite element method (FEM). After optimizing the structural parameters, the sensor exhibits a maximum wavelength sensitivity of 10000 nm/RIU and an amplitude sensitivity of -216 RIU -1 between the two channels. Additionally, each channel of the sensor exhibits its unique maximal wavelength and amplitude sensitivities for different refractive index (RI) ranges. Both channels demonstrate a maximal wavelength sensitivity of 6000 nm/RIU. In the RI range of 1.31-1.41, Channel 1 (Ch1) and Channel 2 (Ch2) achieved their maximum amplitude sensitivities of -85.39RIU -1 and -304.52 RIU -1 , respectively, with a resolution of 5×10 -5 . This sensor structure is noteworthy for its ability to measure both amplitude and wavelength sensitivity, providing enhanced performance characteristics suitable for various sensing purposes in chemical, biomedical, and industrial fields.

π-Conjugation effects on excited-state intermolecular proton-transfer reactions of anthracene-urea derivatives in the presence of acetate anions.

This study investigated emissive urea compounds with an anthryl moiety on one side and a substituent group (biphenyl, naphthyl, benzyl, or cyclohexyl) on the other side across from the urea group. This was performed to determine the contribution of π-conjugation on a substituent group to excited-state intermolecular proton-transfer (ESPT) reactions in the presence of acetate anions. Fluorescence lifetime measurements revealed that the rate constant of the ESPT reaction from the normal form to the tautomer form increased with the length of the π-conjugation. Considering that there were a few differences among the wavelengths of the fluorescence maxima for the anthracene-urea derivatives in the presence of acetate anions, we observed that the extension of π-conjugation promoted tautomer formation. This maintained the energy levels of the normal and tautomer forms in the excited state. Furthermore, an anthracene-urea derivative without π-conjugation did not undergo a reverse ESPT reaction, implying that π-conjugation is considerably involved in the reverse ESPT reaction from the tautomer form to the normal form.

Exceptional three- to six-photon absorption at organometallic dendrimers.

The light-intensity dependence of multi-photon absorption (MPA) affords outstanding spatial control. Furthermore, compared to the higher-energy photons needed for analogous linear absorption, the lower-energy photons involved in MPA often correspond to important wavelengths, such as those of the biological and telecommunications "windows". It is therefore of crucial importance to develop molecules that exhibit outstanding MPA cross-sections. However, although progress has been made with two-photon absorption, there is currently a dearth of efficient instantaneous n-photon absorbers (n > 2), a key reason being the scarcity of structure-property studies required to understand higher-order MPA. We herein report systematically-varied metallodendrimers up to third-generation in size, together with their nonlinear absorptive responses over the spectral range 600-2520 nm. We show that the dendrimers exhibit exceptional instantaneous three- to six-photon absorption cross-sections, with maximal values increasing with dendrimer generation and installation of solubilizing group, and we report that changing the groups at the dendrimer periphery can shift the wavelengths of the nPA maxima. We also describe time-dependent DFT studies that have facilitated assignment of the key linear and nonlinear transitions and disclosed the crucial role of the metal in the outstanding MPA performance.

A novel fluorescence probe for simultaneous detection of mitochondrial viscosity in hepatic ischemia reperfusion injury models.

Acute liver failure caused by hepatic ischemia reperfusion injury (HIRI) poses a severe threat to life, emphasizing the urgent need for precise and timely early diagnosis. Viscosity, a key parameter reflecting active analyte levels at the cellular level, remains underexplored in relation to HIRI. To address this gap, we have developed a groundbreaking near-infrared molecule rotator, PN, exhibiting exceptional characteristics. PN demonstrates remarkable sensitivity, with a 32-fold change in response to viscosity, ranging from PBS to glycerol solution. PN's distinctive features include maximum emission wavelength 790 nm, as well as an impressive Stokes shift 190 nm. Moreover, PN exhibits the ability to sensitively and selectively differentiate nystatin-induced viscosity changes within living cells, and can be used for the detection of viscosity changes in the HIRI mouse model. This capability enhances our understanding of cellular responses, opening avenues for potential applications within disease models. The versatility of PN extends to its potential role in guiding timely monitoring and imaging of viscosity, offering valuable insights into disease progression.

Near-infrared BODIPY photosensitizers for two-photon excited singlet oxygen generation and tumor cell photodynamic therapy.

In this paper, two near-infrared BODIPY photosensitizers, Id-BDPI and Cz-BDPI, were obtained by modifying the indole and carbazole aromatic heterocycles in the core of BODIPY. The maximum absorption wavelengths of Id-BDPI and Cz-BDPI were 694 nm and 722 nm, and their singlet oxygen yields were 48% and 48.4%, respectively. In the simulated tumor cell photodynamic therapy, Id-BDPI and Cz-BDPI could effectively inhibit the growth of A549 tumor cells under near-infrared light. Meanwhile, the lysosomal co-localization coefficients of Id-BDPI and Cz-BDPI with A549 tumor cells were 0.94 and 0.89, respectively, showing high lysosomal targeting ability and biocompatibility. The two-photon absorption cross sections measured at 1050 nm by the Z-scanning method were 661.8 GM and 715.6 GM, respectively, and Cz-BDPI was further successfully applied to two-photon fluorescence imaging and two-photon excited singlet oxygen generation in zebrafish. The above results indicate that the introduction of aromatic heterocycles can effectively enhance the photodynamic efficacy of BODIPY photosensitizers, and the larger two-photon absorption cross section also brings potential for two-photon photodynamic therapy applications.

Biodegradable fluorescent protein chromophore nanoparticles for hypoxic two-photon photodynamic therapy.

In this paper, biodegradable red fluorescent protein (RFP) chromophore analogue DPFP-SS-FA nanoparticles were synthesized for hypoxic two-photon photodynamic therapy. The maximum emission wavelength of DPFP-SS-FA is in the red-to-near-infrared region at 674 nm. Interestingly, these DPFP-SS-FA nanoparticles remain stable under physiological conditions, but deplete glutathione and disintegrate into the RFP chromophore analogue monomer in the tumor microenvironment. Meanwhile, electron paramagnetic resonance data have shown that DPFP-SS-FA produced enhanced 1O2/O2˙- signals after glutathione depletion causing an enhanced PDT effect. DPFP-SS-FA has negligible cell dark toxicity and high phototoxicity in hypoxic environments, indicating the outstanding hypoxia-overcoming ability of DPFP-SS-FA. In addition, due to its folic acid receptor and lysosome dual-targeting ability, DPFP-SS-FA is highly enriched in A-549 tumor cells. In particular, the hypoxic two-photon photodynamic therapy mediated by DPFP-SS-FA nanoparticles was validated in a zebrafish tumor model. Under 800 nm two-photon excitation, DPFP-SS-FA enabled bright two-photon fluorescence imaging and significantly inhibited the growth of tumor cells in zebrafish. The biodegradable DPFP-SS-FA nanoparticles reasonably constructed in this study can serve as excellent candidates for efficient hypoxic two-photon photosensitizers to treat deep tumor tissues.

Effects of metal–metal bonding in photosensitizers: red-shifted absorption and oscillator strength enhancement

Metal–metal bonds facilitate a red-shift in the maximum absorption wavelength and an enhancement of the oscillator strength in photosensitizers.

Donor engineering to regulate fluorescence of a symmetrical structure based on a fluorene bridge for white light emission.

A white organic light-emitting device (WOLED) obtained using blue and yellow complementary colors possesses extremely high optical efficiency. We designed and prepared a completely symmetric D-π-D type efficient blue light small molecule FFA based on octylfluorene as a π bridge, where the undoped device showed efficient blue organic light-emitting device (OLED) performance with a maximum emission wavelength of 428 nm, Commission Internationale de l'Eclairage (CIE) coordinates of (0.17, 0.11) and one of the narrowest full width at half maximum (FWHM) of 35 nm. To improve the matching measure of complementary color materials for achieving white light emission, a yellow light small molecule FCzA was prepared by adjusting the conjugation degree of peripheral electron-donating groups based on the same fluorene-based π bridge with FFA. Undoped devices based on FCzA demonstrated an electroluminescence (EL) emission peak at 576 nm with CIE coordinates of (0.43, 0.49) and a relatively wide FWHM of 130 nm. Ultimately, the white OLED device was modulated with CIE coordinates located at (0.33, 0.38) via proportional regulation with a mixture of FFA and FCzA in a ratio of 10 : 3 as the light-emitting layer.

The stray light induced redshift of absorption peaks of inorganic anions in the far ultraviolet region-an "artifact".

In the analytical process of spectrophotometry, the prerequisite for accurate qualitative and quantitative analysis is obtaining the intrinsic spectra of the analyte. However, the intrinsic properties of spectra can sometimes be masked by easily overlooked non-intrinsic factors, such as those from measuring instruments, leading to erroneous spectral identification. In this study, we documented an unusual redshift phenomenon in the far ultraviolet spectral region. With a spectrophotometer under the nitrogen atmosphere, we selected 14 representative inorganic anions and investigated their absorption spectral behaviors at different optical pathlengths and concentrations. It was intriguing to observe that the absorption peaks with maximum absorption wavelengths below a watershed wavelength of 200 nm underwent a redshift as pathlength and concentration increased, while those above 200 nm did not exhibit a significant redshift phenomenon. In-depth formula simulations and experimental verifications demonstrated that this peculiar spectral behavior was caused by unavoidable stray light in the spectrophotometer. Some methodological and instrumental recommendations are given in the paper. Our study results may serve as a reminder to carefully identify non-intrinsic phenomena when studying absorption spectra in the far ultraviolet region, and provide guidance on spectral corrections in scientific research and practical applications.

Separation and Spectroscopic Determination of Ge(IV) as an Ion Pair Association Complex Using DB18C6 Ligand

A solvent extraction was applied using liquid ion exchange as a sensitive method to extract Germanium (IV) as anion complex K[GeO2(OH)2]- from basic media of KOH by used DB18C6 as a ligand dissolved in chloroform to form the ion pair association complex K-DB18C6+; K[GeO2(OH)2]-, the maximum wavelength of the extracted complex was λmax=290nm, and molar absorptive 1.269and#215;103 L/mol.cm. the Beerand#39;s –lambert law was adhered to within the specified range (1-20)ppm. The limits of detection and quantity were 0.034 and 0.102 ppm, respectively. The research studied optimal conditions of extraction efficiency, such as KOH concentration, shaking time, methanol effect, and electrolyte effect. In addition, a new spectrophotometric method was utilized to determine the remain of Ge(IV) in aqueous solutions and to calculate its distribution ratio (D) using Janus green B. This method was more sensitive when comparing the results with previous studies. DB18C6 as a ligand was used to determine Germanium (IV) in some canned foods widely sold in Iraq.

Study on Marangoni explosion of binary mixtures in liquid layer

In this work, the process of forming micro-droplets due to instability and fragmentation after short chain alcohol solution spreads on the surface of oil layers is studied. Based on the free energy theory of the liquid-liquid interface, the relationship between the binary mixtures spreading on the surface of the liquid layer is derived, and the concentration range of short chain alcohol solution spreading as a thin film on the surface of the oil layer is calculated from the Hiskovsky formula. The Malangoni flow caused by the difference in evaporation rate between the center and edge of the droplet film perturbs the boundary of the liquid film, causing finger-shaped liquid columns to grow at the edge when the droplet spreads to its maximum. In this work, the expression for the critical wavelength and maximum wavelength of boundary instability are derived based on the perturbation model, and the reason for finger shaped liquid column fragmentation is explained based on the Plateau Rayleigh instability. A concentric cylindrical shell liquid column model is established to simplify the calculation and predict the location range of “droplet explosion” of droplets with different viscosity ratios on the liquid layer. Through theoretical calculations and experimental verification, it is found that the alcohol solution fragmented into small droplets within a length range of 4.51–5.98 times the width of the liquid column. This study provides theoretical guidance for existing application fields such as film forming technology and coating technology. The hypotheses, assumptions, and simplified models preliminarily verified experimentally provide solutions for some technical difficulties in the research fields of micro reactions and nanoparticle preparation in chemical industry.

UV- Spectrophotometric technique- based method development and validation for simultaneous estimation of Ciprofloxacin HCl and Quercetin in bulk powder

Antibiotic resistance is increasing worldwide, especially among ocular pathogens and one of the major reasons for this severity is the formation of biofilm which causes antibacterial specialists like Ciprofloxacin HCl to be ineffective, but combining it with substances that inhibit quorum sensing, a process that leads towards the development of biofilm, such as Quercetin, in a single formulation is an effective way to treat these infections. Aiming to develop and approve a new analytical method for the simultaneous evaluation of ciprofloxacin HCl and quercetin in their mass powder, the current examination is expected to accomplish this. Two strategies—the simultaneous equation approach (I) and the absorbance ratio method (II)—were created and validated in accordance with ICH guidelines for specificity, selectivity, linearity, precision, and accuracy. Quercetin's and Ciprofloxacin HCl's absorbance maxima (λmax) were determined to be at 327 nm and 271 nm, respectively, with coefficient correlation values of 0.999 and 0.997. Their isosbestic point was noticed at a maximum wavelength of 283 nm. Both Ciprofloxacin HCl and Quercetin demonstrated linearity in the focus range from 1 µg/ml to 10 µg/ml when absorbances were measured at any of the aforementioned levels. It was discovered that the developed processes were exact and precise with less than 2% relative standard deviation (%RSD). %Recovery studies were found to be 98.62-101.15% for Ciprofloxacin HCl at 271nm, 99.34-100.94% for Quercetin at 327nm, 99.63-104.62%, and 101.23-102.64% for Ciprofloxacin HCl and Quercetin respectively at their isosbestic point. Because it was discovered to be simple, rapid, specific, selective, linear, exact, and based on absorptivity measurements, the established UV Spectrophotometric technique can be used for in vitro depiction and contemporaneous assessment of Ciprofloxacin HCl and Quercetin.

Optical and Electrical Properties of Nano Magnesium Oxide Doped with Polyvinylpyrrolidone (PVP) Thin Films

A thin film of polyvinylpyrrolidone (PVP) polymer doped with different weight ratios of magnesium oxide nanoparticles produced by using the low-temperature hydrothermal method was prepared, and the morphology of the doped thin film was verified using a scanning electron microscope and an atomic force microscope. The X-ray diffraction pattern showed that magnesium oxide has a multi cubic crystal structure with a diffraction peak of high density associated with the level (200) (at the diffraction angle of 42.69◦) and a crystal drop size of 25 nm. Measurements of the Fourier A transformation of the infrared spectrum of a polyvinylpyrrolidone polymer doped with metal oxides was carried out. It showed a clear difference from the pure polymer, where a (Mg-O-Mg) bond appeared at a wavelength of 450 cm^-1 to confirm the effect of MgO addition on the chemical bonding of polyvinylpyrrolidone. Optical properties, including absorbance, maximum wavelength, and energy gap, have been studied. Determined by ultraviolet examination. The band gap decreased when MgO was doped with PVP films, and the Hall coefficient effect was used to calculate the electrical properties, including the conductivity, kinetics of charge carriers, and their type. The highest conductivity was (0.1*10^-2 Sm), and the tainted membrane was of the n type), where it can be used in optical applications.

Oxygen-doped colloidal GaN quantum dots with blue emission

Gallium nitride quantum dots (GaN QDs), as a third-generation semiconductor material, are usually synthesized through a vapor deposition method at an elevated temperature (typically ≥800 °C). Thermal injection method is rarely reported for the synthesis of GaN QDs due to the lack of active precursors and the require of harsh reaction conditions. Here, we report the fabrication of oxygen doped colloidal GaN QDs via rapid thermal injection. By screening the reaction temperature and solvent, well-dispersed GaN QDs with a size of 3.8 nm were obtained in octadecylamine (ODA) at 360 °C. The synthesized GaN QDs show blue emission, the maximum emission wavelength is about 440 nm, and the photoluminescence quantum yield is 14.3%. Furthermore, we reveal the donor-acceptor mechanism of blue emission from GaN QDs. During the growth of GaN QDs, oxygen atoms occupy some nitrogen sites and produce a shallow oxygen donor energy level (ON). A part of the ON can be combined with the adjacent gallium vacancy (VGa) to form a VGa-ON acceptor, whose energy level is about 0.98 eV above the valence band of GaN QDs. The transition of excited electrons from the donor (ON) to the acceptor (VGa-ON) is responsible for the blue emission of GaN QDs.