Optical Materials最新文献

In recent years, the demand for efficient photodetectors within optoelectronic technology has driven the development of layered semiconductor materials at affordable prices. This study focuses on the fabrication of V₂O₅ thin films on glass and p-Si substrates with varying Sr content (0, 1, 3, and 5 wt%) using a cost-effective the perfume atomizer spray technique. The effect of Sr dopant on the morphological, structural, optical and electrical properties of V₂O₅ thin film was examined using standard characterization techniques such as XRD, AFM, UV–Vis, Hall measurement and I–V techniques. Doping V₂O₅ with low Sr content of 1, 3, and 5 wt% significantly impacts the lattice, as evidenced by changes in the orthorhombic structures. The resulting thin films exhibit bandgap values ranging from 2.50 to 2.64 eV. Hall Effect measurements at room temperature revealed n-type conduction for all samples. The study found that doping increases the carrier concentration, leading to a decrease in the resistivity of V₂O₅ by incorporating the dopant into the V₂O₅ matrix. Furthermore, Sr-doped V₂O₅ thin films were deposited on p-Si substrates to form p-n junctions. The voltage-current characteristics of the fabricated diodes were investigated under both dark and illuminated conditions.

A group of glasses with a composition, 5Li₂O−(25-x) Bi₂O₃–10SiO₂–45B₂O₃–15SrO−xNd₂O₃ where x = 0, 0.5, 1, and 2 mol% was prepared to optimize shielding properties. The glass samples were coded as BiBNd0, BiBNd1, BiBNd2, and BiBNd3. Adding Nd₂O₃ instead of Bi₂O₃ reduced the density values, which are 5.098, 4.959, 4.930, and 4.859 g/cm³ for BiBNd0, BiBNd1, BiBNd2, and BiBNd3 samples, respectively. Rising Nd₂O₃ content also reduced the mechanical properties. For example, the Young's modulus values were 69.773, 68.327, 68.387, and 68.320 GPa for BiBNd0, BiBNd1, BiBNd2, and BiBNd3 samples, respectively, which were better than standard glasses of RS520 and RS360. The band gap values varied with the addition of Nd₂O₃, and their values were 2.848, 3.043, 2.613, and 2.665 eV for BiBNd0, BiBNd1, BiBNd2, and BiBNd3 samples, respectively. In addition, the absorption spectrum showed several absorption peaks related to Nd₂O₃ due to the transition from the ground state (4I_9/2) to the excited state of ⁴F_3/2, (⁴F_5/2 + ²H_9/2), (⁴F_7/2 + ⁴S_3/2), ⁴F_9/2, ²H_11/2, (⁴G_5/2 + ²G_7/2), and (²K_13/2 + ⁴G_7/2 + ⁴G_9/2). In addition, adding Nd₂O₃ reduces the neutron and gamma shielding features. For instance, the linear attenuation coefficient (LAC) values of 0.622 MeV for BiBNd0, BiBNd1, BiBNd2, and BiBNd3 were 0.500, 0.485, 0.480, and 0.470 cm⁻¹, which were better than the RS323-G19 and RS360 and they competed with the RS520. At the same time, the transmission factor at 5 cm and 0.662 MeV was 0.082, 0.088, 0.090, 0.09, 0.082, 0.246, and 0.201 for BiBNd0, BiBNd1, BiBNd2, BiBNd, RS520, RS323-G19, and RS360, respectively. Adding Nd₂O₃ instead of Bi₂O₃ reduced the fast neutron removal cross-section from 0.108 to 0.104 cm⁻¹. Lastly, the current glasses showed promising gamma, neutron, and mechanical shielding features better than other standard glasses and materials used in the radiation shielding field.

Terahertz waves exhibit excellent performance in molecular information detection of substances. Since natural materials exhibit weak absorption of terahertz waves, it's conventional to involve mixing analyte with polymer diluents and pressing them into pellets, or enhance the light-material interaction through coupling systems of natural materials with metamaterials. However, both pressure-induced metastable crystal structure transformations and spatial overlap between the analyte and metasurfaces can impact the absorption of terahertz waves by organic crystals. This paper proposes a novel analytical approach using paraffin as a dilution matrix for qualitatively and quantitatively characterizing organic crystals with THz spectroscopy. The featureless refractive index spectra and negligible absorption demonstrated the feasibility of paraffin as a diluting analyte. The analytical process was further demonstrated with well-studied lactose by being diluted in molten paraffin at different mass-ratios and solidified as pellets under room temperature and ambient pressure. A continuous wave terahertz frequency domain spectroscopy system (THz-FDS) is used for spectral acquisition over 0.4–1.3 THz. The experimental results reveal a significant linear correlation between the absorption coefficient peak areas and molar concentration of lactose, with a correlation coefficient R² of 0.9678. Our method provides an additional optional dilution matrix for terahertz spectroscopy characterization of organic crystals, enabling non-destructive, rapid, and direct measurement of metastable crystals. Furthermore, this study on paraffin as a binder material holds potential for enhancing spatial overlap between natural materials and metamaterials in the field of metasurface-enhanced sensing.

PbS colloidal quantum dots (CQDs) have important applications in short-wave infrared (SWIR) detection due to its wide tunable bandgap, low thermoelectric noise, and solution processing capability. Due to the exciton peak of QDs determines the response band of the detector, while QDs with good monodispersed often exhibit better optical performance in photodetectors. The detection performance of PbS CQD-based SWIR photodetectors is closely related to the synthetic properties of QDs in the active layer. In addition, the emergence of machine learning in recent years has accelerated the exploration of QDs synthesis processes. Here, a framework is developed by neural network model which can learn from existing experimental data, through proposed experimental parameters for try, and ultimately point to regions of synthetic parameter space, thereby rapidly and accurately predicting the exciton peak and peak/valley ratio of synthesized CQDs. In terms of model performance, the NN model achieved a correlation coefficient of 0.93 for exciton peak prediction, which is very close to 1. For peak/valley ratio prediction, the correlation coefficient reached 0.75. In prediction of the latest synthesized CQD, the prediction error of exciton peak is only 3.89 %, and the prediction error of peak/valley ratio is 7.24 %. Furthermore, this batch of well synthesized monodisperse CQDs with a peak/valley ratio of 3.105 were used to prepare SWIR photoconductive devices, which demonstrates an excellent device performance, with the responsivity achieving 2.53 A/W, the detectivity reaching up to 2.08 × 10¹² Jones and the noise current of only 7.81 × 10⁻¹³ A/Hz^1/2. This work provides an effective method for preparing PbS CQD of various waveband with uniform particle size, which is expected to reduce costs for high-performance SWIR photodetectors.

We report on the crystal growth, polarized spectroscopy, and laser operation of monoclinic Tm³⁺, Na⁺(Li⁺) codoped zinc monotungstate (ZnWO₄) crystals. The Li⁺ codoping with an optimized Tm/Li ratio enables almost complete local charge compensation leading to better crystal quality, higher Tm segregation coefficient, and longer luminescence lifetime and ultimately the demonstration of laser operation. The modified Judd-Ofelt theory was employed to calculate the Tm³⁺ transition probabilities yielding a radiative lifetime of the ³F₄ state of 2.59 ms. The corresponding intensity parameters are Ω₂ = 5.194, Ω₄ = 0.658, Ω₆ = 0.471 [10⁻²⁰ cm²] and α = 0.110 [10⁻⁴ cm]. Tm,Li:ZnWO₄ features strongly polarized emission spectra extending beyond 2 μm owing to a large total Stark splitting of the ground-state, ΔE (³H₆) = 644 cm⁻¹. The stimulated-emission cross-section in this spectral range reaches 0.47 × 10⁻²⁰ cm² at 2015 nm for light polarization E || N_p. The continuous-wave Tm,Li:ZnWO₄ laser generated 282 mW at 1.98 μm with a slope efficiency of 14.7 %, and laser emission at 2.03 μm was also achieved.

Solar spectral conversion by a low-cost luminescent coating for greenhouse applications increases crop yield and can contribute to addressing the food crisis. A luminescent coating based on cheap SiO₂ particles doped with Eu²⁺ and Al³⁺ demonstrated extra photosynthetic active radiation (PAR) in this work. To optimize the efficiency of this phosphor for greenhouse applications, three phosphor series with varying Al/Eu content in SiO₂ were synthesized via a sol–gel approach and characterized by luminescence decay time, absorption, luminescent excitation, emission, and quantum yield measurements. With increasing the Eu%, at a fixed Al%, the decay time and quantum yield decreased while the emission shifted to the red. The effect can be explained by a more and more efficient resonance energy transfer to lower energy Eu²⁺ ions and quenching sites. While increasing the Al% at a fixed Eu%, the decay time and quantum yield increased, and the red-shift was reduced. Both effects can be explained by an enhanced Eu²⁺ solubility (reduced Eu clustering) through the Al³⁺ co-doping, causing the average Eu²⁺-Eu²⁺ distance to be longer and the onset of concentration quenching to shift to a higher Eu%. Specifically, we found that for 1 mol% Eu²⁺, a minimum of 4 mol% Al³⁺ was required to avoid concentration quenching. Two indicators were developed to quantify the UV to PAR converting efficiency and to quantify the PAR transmission enhancement. Both indicators were determined in a real coating sample based on the optimized phosphor. The result showed an additional PAR was provided by our luminescent coating. A general discussion about all factors that can bring the conversion efficiency of a phosphor coating closer to the theoretical maximum will be presented.

Our study examines how the concentration of scatterers affects the intensity threshold of random laser (RL) action in colloids made of niobium oxide particles and Rhodamine B dye. This is the first reported instance of RL action in niobium oxide. We kept the dye (gain medium) concentration constant and quantified how varying concentrations of niobium oxide particles (scatterers) affect the RL intensity threshold. Our findings indicate an inverse relationship between the concentration of niobium oxide particles and the RL threshold. Increasing the niobium oxide concentration from 0.32 mM to 2.50 mM decreased the RL threshold by up to 70 %, suggesting that higher scatterer densities lead to enhanced efficiency of the lasing process. We noticed that the RL intensity thresholds decrease concerning scatterer concentration, highlighting the significant impact of scatterer density on lasing efficiency. These results could provide a better comprehension of the mechanics of RL in disordered media and emphasize the essential role of scatterer density in determining RL efficiency. Our work deepens the understanding of RL dynamics and lays the groundwork for designing and optimizing colloidal RL systems for various applications such as imaging and optical sensing.

Here, we studied the effect of the MoO₃ thin film thickness on the ultraviolet (UV) and infrared (IR) photodiode properties of the n-MoO₃/p-Si heterojunction structure. Initially, the metal molybdenum (Mo) thin films with different thicknesses (50,150, and 250 nm) were created via DC magnetron sputtering on a p-type Si substrate. Then, the MoO₃ thin films were synthesized using a thermal oxidation method with an optimal oxygen flow rate of 60sccm. XRD and Raman analysis showed that the structure of prepared thin films has converted from an amorphous to an orthorhombic (α-MoO₃) crystalline phase with increasing thickness. The optical transmittance of the layers was tuned by controlling the thickness, and the maximum transmittance for the 50 nm-thick film was achieved in the broad wavelength range of 300–1100 nm. The current density–voltage (J–V) characteristics indicate the prepared samples' rectifying behavior under dark conditions. The heterojunction photodiode with a 50 nm-thick MoO₃ layer shows the best performance. This sample had a maximum amount of transmittance in the UV–visible and IR regions, compared to other samples, which leads to efficient electron-hole separation and transportation. This sample demonstrates a significant photoresponse ratio (I_Light/I_Dark) of about 55 and 52.5 in the ultraviolet (UV) and infrared (IR) regions, respectively.

Multiple emissive carbon dots (CDs) were synthesized through a one-step solvothermal acid-assisted method using citric acid and urea. Three main emission bands were observed at ∼431 nm, ∼501 nm, and ∼622 nm, corresponding to excitation wavelengths of 360 nm, 430 nm, and 550 nm, respectively. Simultaneous detection through salient discernible features of three metal ions has been achieved. Emission of CDs with Fe(III) shows reduction in intensity at 360 nm and 550 nm wavelengths and an enhancement of photoluminescence (PL) intensity at an excitation wavelength of 430 nm. Al(III) revealed turn-on PL signals, along with a redshift when excited at 360 and 430 nm, and turn-off intensity at excitation of 550 nm. Under all the excitation wavelengths, Cr(VI) exhibits PL quenching accompanied with an additional red shift. This sensor enhances the accuracy and reliability of the probe through multiple distinctive and characteristic responses for all the three ions for which the probes were selective. Apart from the optical detection at a certain wavelength, the Cr(VI) reduction to the less toxic Cr(III) through as-prepared CDs could be monitored at three different excitation wavelengths. The Fe(III) and Cr(VI) detection in solid state has also been demonstrated through 2D luminescent photonic structures formed with CDs-PVA (poly-vinyl alcohol)-polyNIPAM (poly (N-isopropylacrylamide)) composites that can possibly be used for anticounterfeiting applications.