Er-doped ZnO Research Articles

Dual Eu3+ and Er3+ doping in ZnO nanoporous 2D frameworks for tuning photocatalytic activity, linear and non-linear optical response

Recent days, the greater attention of research materials are focusing on the porous nano frame structure due to their distinctive properties and high photocatalytic activity. The porous defective materials revealed a significant role in numerous research fields like sensors, catalysts, energy production, magnetic memory storage, bio medical etc. In our work, pure ZnO and 4f shell shielded rare earth metals doped ZnO metal oxide nanomaterials attributed in the photocatalytic dye degradation, non-linear optical and magnetic properties. We were synthesized pure ZnO and ZnO0.1–2xEuxErxHMT0.1–2x (2x = 0.025,0.05,0.075, 0.010 wt%) nanoparticles using a straightforward hydrothermal route. The hexagonal wurtzite structure of ZnO and Eu:Er-doped ZnO (Eu:Er@ZnO) exhibited by PXRD, and the optical bandgap (Eg) range from 3.14 eV to 3.18 eV was determined by Tauc relation (αhγ)2 = 0. The porous nanoplate morphology of as-synthesized materials revealed by HR-SEM and HR-TEM techniques. All synthesized materials exposed weak ferromagnetic property nature by VSM studies. Among all the synthesized materials, the 0.0025 wt% Eu:Er@ZnO nanoparticles exhibited porous nanoplate structures capable of catalyzing the breakdown of reactive black 5 (RB5) dye, achieving a photocatalytic activity of 93.2 % after 65 min of UV light exposure. The dopant concentration significantly influenced this photocatalytic activity, with lower concentrations showing enhanced performance, particularly in acidic conditions. Moreover, all synthesized porous nano-plate materials followed pseudo-first-order kinetics. Additionally, the Z-scan technique was employed to assess the nonlinear optical properties of the synthesized materials using Q-switched nanosecond Nd laser pulses at 532 nm wavelength. The open-aperture Z-scan revealed reverse saturable absorption (RSA) in all samples. The Eu:Er@ZnO porous nano-plates exhibited promising nonlinear absorption characteristics, with a higher nonlinear absorption coefficient ranging from 5.21 to 7.84 × 10−11 m/W and a lower optical limiting threshold between 0.87 and 0.95 × 1012 W/m2.

Green Synthesis of Er-Doped ZnO Nanoparticles: An Investigation on the Methylene Blue, Eosin, and Ibuprofen Removal by Photodegradation.

We present a study on the green synthesis of undoped and Er-doped ZnO compounds using Mangifera indica gum (MI). A set of tests were conducted to assess the structure of the material. The tests included X-ray diffraction, Raman, and Fourier-transform infrared spectroscopy. Optical properties were studied using diffuse reflectance and photoluminescence. Morphological and textural investigations were done using SEM images and N2 adsorption/desorption. Furthermore, photocatalytic tests were performed with methylene blue (MB), yellow eosin (EY), and the pharmaceutical drug ibuprofen (IBU) under UV irradiation. The study demonstrated that replacing the stabilizing agent with Mangifera indica gum is an effective method for obtaining ZnO nanoparticles. Additionally, the energy gap of the nanoparticles exhibits a slight reduction in value. Photoluminescence studies showed the presence of zinc vacancies and other defects in both samples. In the photocatalytic test, the sample containing Er3+ exhibited a degradation of 99.7% for methylene blue, 81.2% for yellow eosin, and 52.3% for ibuprofen over 120 min. In the presence of methyl alcohol, the degradation of MB and EY dyes is 16.7% and 55.7%, respectively. This suggests that hydroxyl radicals are responsible for the direct degradation of both dyes. In addition, after the second reuse, the degradation rate for MB was 94.08%, and for EY, it was 82.35%. For the third reuse, the degradation rate for MB was 97.15%, and for EY, it was 17%. These results indicate the significant potential of the new semiconductor in environmental remediation applications from an ecological synthesis.

A comparative photocatalytic degradation study of Thymol blue dye over pristine ZnO and Er-doped ZnO

A comparative photocatalytic degradation study of Thymol blue dye over pristine ZnO and Er-doped ZnO

Engineering Er-doped ZnO nanocrystals for As-removal: Targeting water remediation

Erbium-doped zinc oxide nanocrystals (Zn1−xErxO) produced by the polymeric precursor method are the subject of a comprehensive study in this report. Our results indicate that only the wurtzite ZnO phase is produced up to x = 0.050. After that (x > 0.050), a mixed system with a secondary phase (Er2O3) is found. The lower solubility limit of erbium in the ZnO crystal lattice is correlated with the higher ionic radii of Er3+-ions compared to Zn2+-ions, impacting remarkably the solid solution limit. Magnetic measurements show the coexistence of the two phases: paramagnetism (PM) related to Zn1−xErxO nanocrystals (free and short-range coupled Er3+-ions) and a weak ferromagnetic (FM) contribution assigned to the presence of bound magnetic polarons. UV–vis spectra show a transition from one to two excitonic peaks as the Er-content increases; the second peak related to the nucleation process of the secondary Er2O3 phase, which was successfully acknowledged using the Elliott’s model. Fourier transform infrared (FTIR) spectroscopy was used to characterize vibrational properties and the results are in agreement with the x-ray diffraction data analysis. To assess the efficiency of using the Zn1−xErxO samples to remove As(V) from contaminated water, a reference water solution containing 500 ppb As(V), at a neutral (pH = 7), was prepared to simulate drinking water. Our results show the effectiveness of As-removal. It was determined that the effectiveness is improved with the Er-content, reaching the limit imposed by World Health Organization. According to the linearity achieved while applying the pseudo-second-order-adsorption model, our findings strongly suggest that a chemisorption mechanism takes place between the Zn1−xErxO nanoparticle surface and As(V) in solution.

Effect of Cr cations addition on the structural, morphological, optical, and photocatalytic properties of Er-doped ZnO structures

In this work, we have investigated the effect of Cr3+ cations addition on the structural, morphological, optical, and photocatalytic properties of Er-doped ZnO structures. The Zn(1-(x-y))ErxCryO compound, where [(x; y) = (0.00; 0.00), (0.02; 0.01), (0.02; 0.02) and (0.02; 0.03)] was synthesized by the co-precipitation method and thermally treated at 100 °C for 6 h. The structural study showed that the dopant cations concentrations, cause variations in lattice constants, and increase the crystallite size and the strain in the ZnO crystal lattice. The structural atomic disorder was confirmed by Raman and photoluminescence spectroscopies, with VO, VO+, and VO++ type oxygen vacancy defects dominating. The samples exhibited different morphologies depending on the dopant concentration (plates-like, irregular hemispherical particles, and octahedrons-like structures). In the photocatalytic test, the methylene blue (MB) dye degradation under UV irradiation increased as a function of Cr3+ cations concentration, achieving a degradation rate of 37.4 ± 1.9% for the sample containing 2% of Er3+ cations and 3% of Cr3+ cations. In addition, the MB dye removal capacity by the Zn(1-(x-y))ErxCryO compound was incremented to above 85% using an optimized H2O2 concentration. Finally, the irradiated solution did not show toxicity against Artemia salina, indicating that the intermediate photoproducts formed are not toxic.

Remarkably enhanced piezoelectric and ferroelectric characteristics of Er:ZnO upon graphene addition for wearable self-powered piezoelectric sensors

Flexible Er-ZnO/PDMS and Er-GO/ZnO/PDMS nanogenerators with high energy harvesting performance were developed. The output voltage and current density of Er-doped ZnO, Er-doped GO/ZnO (1:10) and Er-doped GO/ZnO (1:5) nanocomposites-based piezoelectric harvesters were (70 V, 1.85 µAcm−2), (80 V, 2.16 µAcm−2) and (100 V, 2.47 µAcm−2), respectively. The Er-doped GO/ZnO wearable sensor showed output voltages of 4 V and 9 V by bending the human wrist and elbow, respectively. In addition, a remarkable improvement of the remnant polarization (Pr) and a favourable reduction of the coercive field (Ec) were achieved for Er-doped ZnO and Er-doped GO/ZnO nanocomposites. The corresponding values of Pr and Ec for pure ZnO, Er-doped ZnO, Er-doped GO/ZnO (1:10) and Er-doped GO/ZnO (1:5) nanostructures were (0.06 μC/cm2, 6.50 kV/cm), (8.75 μC/cm2, 4.74 kV/cm), (13.25 μC/cm2, 3.98 kV/cm) and (8.913 μC/cm2, 3.54 kV/cm), respectively. The enhanced piezoelectric and ferroelectric properties of Er-doped ZnO and Er-doped GO/ZnO nanocomposites make them futuristic hybrids with immense potential for designing pressure biosensors, mechanical energy harvesters and environmentally friendly ferroelectric-based memory devices.

New insights on the luminescence properties and Judd-Ofelt analysis of Er-doped ZnO semiconductor quantum dots.

In this study, Er3+ doped ZnO semiconductor quantum dots (QDs) were synthesized using a wet chemical method. The successful doping of Er3+ ions into the ZnO host lattice and the elemental composition was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The ZnO and Er3+ doped ZnO QDs with a hexagonal structure, spherical shape, and particle size of approximately 5 nm were revealed by XRD and transmission electron microscopy (TEM). The absorption, luminescence properties, and fluorescence lifetimes of the samples were studied as the concentration of Er3+ ions varied. The intensity parameters, emission transition probabilities, branching ratios, and emission lifetimes of the excited levels of Er3+ ions in the ZnO host were determined using the Judd-Ofelt theory, which provided insight into the covalent relationship between the ions and ligands as well as the nature of the ZnO host lattice. Moreover, the energy transfer process from the ZnO host to Er3+ ions and the yield of this process are explained in detail along with specific calculations. The Er3+ doped ZnO QDs displayed a significantly longer lifetime than undoped ZnO, which opens up many potential applications in fields such as photocatalysis, optoelectronics, photovoltaics, and biosensing.

Preparation, characterization and photocatalytic properties of Er-doped ZnO nanoparticles synthesized by combustion method

Abstract Erbium-doped zinc oxide (Er-doped ZnO) as a visible-light-driven photocatalyst was prepared by combustion method and followed by calcination at 600 °C for 2 h. The samples were characterized by means of X-ray diffraction, Raman spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. X-ray diffraction patterns of ZnO samples with and without Er dopant confirm the formation of pure hexagonal wurtzite ZnO phase. The X-ray diffraction peaks of ZnO were shifted to the lower 2θ angle when Er was doped to ZnO matrix. Their transmission electron microscopy images show that the addition of Er can play a role in significantly changing their particle size. Average particle sizes of the as-prepared samples were 69.15 ± 14.47 nm, 68.33 ± 17.06 nm, 16.38 ± 4.02 nm and 27.00 ± 5.27 nm for 0 %, 1 %, 3 % and 5 % Er-doped ZnO samples, respectively. Raman spectra of the Er-doped ZnO samples were able to be used to identify the presence of defect and structural disorder in the ZnO lattice. The ZnO samples with and without Er dopant were tested for the degradation of methylene blue under visible light irradiation. Upon increasing the doped Er content, the degradation of methylene blue solution under visible light irradiation was enhanced. In this research, the 3 % Er-doped ZnO nanoparticles have the highest efficiency of 98.26 % under visible light irradiation within 100 min.

Influence of Er substitution on the properties of ZnO: A comprehensive study

Er-doped ZnO (Zn(1-x)Er(x)O) films with (002) preferential orientated wurtzite structure were fabricated on a c-plane sapphire substrate by pulsed laser deposition (PLD). The effects of Er composition, oxygen pressure during growth, and post-growth annealing on the films' structural, electrical, and optical properties were studied by employing a comprehensive spectroscopic approach. Er-doped ZnO films with a resistivity of 4 × 10−4 Ωcm, electron conductivity n+∼1021 cm−3, and high optical transmittance (>90%) were disclosed to be appropriate candidates for transparent conducting electrode applications. A shallow donor is reported to be associated with the ErZn defect, which is optically inactive. Er-doped ZnO samples grown with high Er composition and oxygen pressure don't show n+ conductivity because of the formation of an O-rich ErZn-related compensating defect. Annealing at 750 °C converts the ErZn shallow donor to another defect configuration, which is optically active for intra-4f-shell transition emissions, but no longer a shallow donor. The growth condition for maximizing the intra-4f-shell transition emission was also obtained.

Optimization of the luminescence and structural properties of Er-doped ZnO nanostructures: effect of dopant concentration and excitation wavelength

The present study reports the effect of Er doping on the structural, morphological, and optical properties of ZnO nanostructures. ZnO: Er nanorods with different doping concentrations were successfully synthesized via a hydrothermal method. X-ray diffraction and Energy-dispersive X-ray spectroscopy analyses suggest the successful incorporation of Er into the wurtzite structure of ZnO; A secondary phase of Er2O3 appears when the Er concentration exceeds 2.5 wt%. The optical band-gap of ZnO was determined from the analysis of ultraviolet–visible spectra, and a decrease of the band gap is emphasized with increasing Er concentration. Photoluminescence spectra display a strong and broad deep-level emission band, which intensified with increasing Er concentration. The current work provides more details about the excitation wavelength effect on the luminescence of pure and Er-doped ZnO materials, finding that the visible photoluminescence emission intensity could be controlled by adjusting the Er concentration as well as the excitation wavelength; better luminescence was obtained with high Er concentration and high excitation wavelength. Moreover, the DFT calculations support the experimental results and confirm that the presence of oxygen vacancies has an effect on the structural and electronic properties of ZnO. Hence, the research findings of this work could provide an experimental and theoretical reference that may motivate future research on the study of ZnO-based optoelectronic applications.

Erbium-doped ZnO nanoparticles for anode materials: A comparative study using anthocyanin and curcumin dyes in DSSC

Nanomaterials doped with rare earth ions have attracted increasing interest in the renewable energy harvesting field. Erbium-doped ZnO nanoparticles were prepared by the solution polymerization method. The hexagonal wurtzite structure of ZnO was preserved, according to X-ray diffraction (XRD) studies, and the average crystallite size is less than 20 nm. The UV–Vis spectroscopy revealed that the optical band gap was 3.1 eV, with peaks associated with erbium-specific electronic transitions appearing when the doping concentration was raised (Er). Anthocyanin and curcumin dyes were employed to build dye-sensitized solar cells devices (DSSCs) employing nanoparticles as photoanodes. When compared to undoped ZnO, Er-doped ZnO at 1.25 at. percent improves power conversion efficiency (PCE) by 200% for anthocyanin dye and 10% for curcumin dye.

Charge trapping processes in hydrothermally grown Er-doped ZnO

Influence of X-ray irradiation on luminescence properties and defects creation was studied in the erbium doped hydrothermally grown ZnO by using the combination of photo- and radioluminescence (PL and RL), thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR). The photoluminescence properties of the ZnO:Er appeared affected by the X-ray irradiation – the intensity of the zinc vacancy-related red band and exciton-related ultraviolet band were weakened. The irradiation also evoked charge trapping and new centers creation whose type and number depended on Er doping. The X-ray induced defects were oxygen-based hole and electron trapping centers, O− and O2−, respectively. The X-ray irradiation had also influence on shallow donors in the bulk and at the surface of the ZnO nano- and microrods. TSL glow curves consisted of one broad peak with the maximum at about 110 K, its intensity was varying with the changing Er content. The glow peak was correlated with the thermal destruction of the unstable O2− electron trapping centers. Zinc vacancies-based defects participated in the thermally stimulated luminescence as recombination centers for the electrons released from the O2−.

A DFT study on the electronic structure, magnetic and optical properties of Er doped ZnO: Effect of Er concentration and native defects

We report on first-principles study of the effect of Er concentration and intrinsic defects (VO and VZn) on the electronic structure and optical properties of Er-doped ZnO using the GGA + U method. The lattice constants and band gap of ZnO calculated in this work are in agreement with experimental values. The results showed that the band gap of Er-doped ZnO decreases with increasing Er concentration, while it increases with the presence of O or Zn vacancies. Furthermore, the existence of VO causes the formation of a deep donor level in the band gap. Er–ZnO + VZn is a degenerate p-type semiconductor, and shallow acceptor states are created near the Fermi level. The magnetic moment of doped ZnO increases and Er 4f electrons are responsible for the induced magnetic moments. The absorption coefficient enhances in the visible range in Er doped ZnO. In the Er–ZnO + VO model, both absorption and reflection are relatively enhanced in the visible range, leading to a decrease in light transmittance. Hence, the magneto-optoelectronic properties of ZnO could be improved by an optimal concentration of Er as well as with the presence of oxygen vacancies.

Er-Doped ZnO, CuO and Pentacene Based Broadband Photodetector With High External Quantum Efficiency

This letter reports an Er-doped ZnO (EZO), CuO and Pentacene ternary nanocomposite (NC) thin film based Al/Pentacene:CuO:EZO/PEDOT:PSS/ITO broadband photodetector using low-cost solution method. The NC film shows light absorption in a broad spectral range covering the ultraviolet (UV)-visible-near infrared (NIR) region. The device shows high very external quantum efficiencies (EQEs) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.4\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.6\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.5\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> at 350 nm (UV), 600 nm (visible) and 1050 nm (NIR), respectively, under a reverse bias of −1 V. This high EQE is attributed to trap-assisted charge injection at the NC/Al interface under reverse bias. Characterizations of multiple fabricated devices are used to show repeatability and stability of the proposed photodetector.

Constructing Er-Doped ZnO/CuS/Au Core-Shell Nanowires with Enhanced Photocatalytic and SERS Properties

In this study, we fabricated Er-doped ZnO/CuS/Au core-shell nanowires using two-step wet chemical methods and an ion-sputtering method on a glass substrate as a bifunctional photocatalytic and surface-enhanced Raman scattering (SERS) substrate. The characteristic properties of as-prepared photocatalysts were confirmed by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy, DR/UV-Vis spectroscopy, and photoluminescence spectroscopy. Compared with Er-doped ZnO nanowires and Er-doped ZnO/CuS core-shell nanowires, Er-doped ZnO/CuS/Au core-shell nanowires exhibited remarkably photocatalytic activity to degrade acid orange 7 solutions under blue LED light. These results ascribed to the Er-doped ZnO/CuS/Au core-shell nanowires can enhance the visible-light absorbance and the separation efficiency of photogenerated electron-hole pairs, inducing their higher photocatalytic activity under blue LED light. In addition, Er-doped ZnO/CuS/Au core-shell nanowires exhibit high sensitivity, a low detection limit (10−6 M), uniformity, recyclability, and stability of SERS performance for detected acid orange 7.

Pentacene and Er-Doped ZnO Nanocomposite Based UV-Visible-NIR Wideband Photodetector

This letter reports a Pentacene and Er-doped ZnO (EZO) nanocomposite (NC) based wideband photodetector working in ultraviolet (UV), visible and a part of the near-infrared (NIR) regions. The proposed device consists of Al/Pentacene:EZO/PEDOT:PSS/Indium Tin Oxide (ITO) structure using a low-cost solution method. The Pentacene:EZO NC shows a wide absorption spectrum covering UV-visible-NIR regions. At a reverse bias of −1 V, the measured responsivity values (A/W) of the proposed device are 23.36, 18.41, and 206.97 at 300 nm (UV), 660 nm (visible) and 980nm (NIR), respectively. The reproducibility of the proposed structure is also analyzed in the letter.

Multifunctional and smart Er2O3-ZnO nanocomposites for electronic ceramic varistors and visible light degradation of wastewater treatment.

In this proposed study, erbium (Er3+)-doped ZnO nanocomposites were prepared through the effective, basic, and green combustion method. The significant effects of Er dopants on the structural, morphological features, dielectric, and optical behaviors of the pure ZnO matrix as well as Er2O3-ZnO nanostructured materials were investigated applying X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformation infrared (FT-IR) spectroscopy, and UV-Vis spectrophotometer techniques. These results showed that the synthesized Er2O3-ZnO nanocomposites are well polycrystalline. The Er2O3-ZnO nanocomposites are almost uniformly distributed on the surface morphologies. Furthermore, UV-Vis diffuse reflectance spectroscopy, AC electrical conductivity, and dielectric properties' current-voltage characteristics were utilized to examine the influence of erbium doping on the optical properties, energy bandgaps of the proposed Er2O3-ZnO nanostructured powder. The tested nano-samples were applied for the visible light photodegradation of p-chlorophenol(4-CP) and p-nitrophenol (4-NP). The Er-doped ZnO ratio affects the photocatalytic activity of the ZnO matrix. This current research substantiated that more than 99.5% of 4-CP and 4-NP were photodegraded through 30 min of irradiation. Four times, the Er:ZnO nanocatalysts were used and still displayed an efficiency of more than 96.5% for 4-CP and 4-NP degradations in the specified period of 30 min. The as-prepared Er2O3-ZnO nanostructures are considered novel potential candidates in broad nano-applications from visible photocatalytic degradation of waste pollutants to the electronic varistor devices.

Enhancement of magnetic moment of Er-implanted ZnO films by post-annealing in Ar and vacuum

The Er ions have been introduced into ZnO films prepared by radio-frequency magnetic sputtering (RFMS) on sapphire substrates by ion implantation. The annealing effect on structural and magnetic properties for Er-implanted ZnO films under air, Ar, and vacuum atmospheres at 650 °C have been investigated systematically by a combined characterization of X-ray diffractions, Raman spectroscopy, Photoluminescence, X-ray photoelectron spectroscopy and Superconducting Quantum Interference Device. Strong room-temperature ferromagnetism has been observed for the as-implanted and annealed films. We found that the saturation magnetization varied greatly for different annealing conditions. A considerable enhancement in magnetization is observed for Er-doped ZnO annealed in vacuum, which is accompanied by an enhancement in the concentration of oxygen vacancy. Our results give clear evidence that the enhancement of ferromagnetism is strongly correlated with the increase of oxygen vacancies in Er-doped ZnO.

Effects of rare earth elements doping on gas sensing properties of ZnO nanowires

The effects of rare earth elements (Ce, Eu, and Er) doping on the microstructure and gas sensing properties of ZnO nanowires were investigated. The Ce, Eu, Er-doped ZnO nanowires and pristine ZnO nanowires were synthesized via a solvothermal route. The structure of the prepared samples was studied and compared by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron microscopy. The gas sensors were fabricated by coating the prepared samples on aluminum oxides tube-based Au sensing electrode, with Ni-Cr heating wire to control the operating temperature. The operating temperature of all sensors was determined to be 300 °C with consideration of ethanol response. At this temperature, all sensors showed good ethanol sensing performance, with the 1%Ce-doped ZnO nanowires-based sensor exhibited the highest ethanol response over the other sensors. The mechanism for the microstructure and gas sensing behavior difference of various samples was discussed.

Tailoring Stark effect in the 1.54 µm emission of Er-doped ZnO thin films

We report a study on the infrared optical emission of Er3+ inserted on ZnO hosts. The doping process was carried out during the growth of thin films by spray pyrolysis. The precursor solutions consisted of zinc acetate and erbium chloride proportionally diluted in distilled water, producing films in a clean and cost-effective process. The different molarity conditions employed here, M=10−3 and M=10−1, provided the growth of high textured c-axis, optical transparent ZnO, and white powder-like ZnO films, respectively. The infrared emissions at 0.8 eV (1.5 μm) are affected by the level manifolds due to the Stark effect, which is found to be strongly dependent on synthesis parameters. Lower crystallinity implies mitigation of the strong electric field in c-direction, reducing the intensity of the splitting caused by Stark effect.