Introduction

The periodic table comprises a group of elements that are known as rare earth elements, containing lanthanum (La) and erbium (Er) which are a part of the lanthanide series. The rare earth elements (REEs) are categorized into light and heavy groups. REEs are categorized by atomic number and weight. The two groups known are the heavy rare earth elements and light rare earth elements. The ten heavy rare earth elements are ytterbium, erbium, terbium, dysprosium, holmium, gadolinium, lutetium, europium, thulium and yttrium [1]. The light rare earth elements include cerium, praseodymium, lanthanum, neodymium, promethium, and samarium. Wind turbines, LED light bulbs, TV, cell phones, computers, memory, and solar panels rely on REEs. All high-tech devices contain these crucial elements. Flat-panel televisions use all REE. Smart batteries used in hybrid vehicles and to power all-electric often contain various REE compounds. These elements offer reduced energy consumption, increased efficiency, smaller size, faster speed, extended durability, and heat resistance. Demand for green technology has increased in recent years [2]. Analytical instruments are becoming smaller and more efficient with the help of these technologies.

Rare earth luminous materials have a wide range of applications in different fields. They can be used for industrial such as metal and glass production. Rare earth nano-powder added to epoxy resin improved toughness, high-temperature resistance, and strength. It also improved overall performance with a small amount of material and low cost [3]. Organic silicon materials can have increased high-temperature resistance and ultraviolet resistance. Lanthanum erbium telluride (LaErTe) nanomaterials resist high temperatures, radiation, and ultraviolet light. LaErTe ions are used for high-energy detectors. These scintillators can be used in many ways to detect cosmic rays in biomedical tests.

LaErTe nanomaterials have high capacitance than other transition metal oxides. The nanomaterials have good conductivity, large surface area, and strong cycle stability [4,5]. Changing the form and size of rare-earth nanomaterials can increase their electronic conductivity. The nanostructuring of LaErTe material increases surface area [4-6]. The shape exposes active sites and high-energy crystal planes, giving the material a longer cycle life. Mixing rare earths with other transition metal chalcogenides can improve pseudo-capacitance and cycle efficiency [6-11]. Distinct properties and structures are found in rare earth elements. Rare earth-based nanomaterials have gained attention due to their environmentally safe qualities and exceptional redox capabilities. There are various techniques available for synthesizing rare-earth-based nanomaterials, including Hydrothermal, electrodeposition [12–20], thermal decomposition, micro-emulsion method, atomic layer deposition, thermal oxidation, sonication, sputtering, electrochemistry, physical vapor deposition, and combustion methods, which are ecologically safe, cost-effective, and straightforward [1,9]. Hydrothermal synthesis is considered one of the most crucial and well-established processes for nonmaterial synthesis due to its effectiveness and reliability [1,3,6,9]. This process uses an enclosed and heated device, like an autoclave or bomb calorimeter, and involves chemical reactions using water as a solvent.

In this study, we use hydrothermal technique to synthesize the nanoparticle of lanthanum erbium telluride (La_0.1Er_0.2Te_0.2) using 0.2 mol of Er(NO₃)₃·5H₂O, 0.1 mol of La(NO₃)₃·6H₂O, and 0.2 mol of Te(NO₃)₄ and study the impact of annealing temperature on the structural, optical, morphological, and electrical features of the material.

Experimental Details

Materials

The materials used in this work include lanthanum nitrate hexahydrate (La(NO₃)₃ ·6 H₂O) Sigma-Aldrich 99.9%, erbium trinitrate pentahydrate (Er(NO₃)₃·5H2O) Sigma-Aldrich 99.9%, tellurium nitrate (Te(NO₃)₄), distilled water, heating mantle, power source, Multimeter, fluorine-doped tin oxide as the substrate (FTO), thermostatic blast resettable oven within a temperature range of 50 °C - 1000 °C.

Synthesis of lanthanum erbium telluride (La_0.1Er_0.2Te_0.2)

Lanthanum erbium telluride (La_0.1Er_0.2Te_0.2) was prepared using the hydrothermal technique. 25 mL of water was used to dissolve 0.2 mol of erbium trinitrate pentahydrate (Er(NO₃)₃·5H2O) and 0.1 mol of lanthanum nitrate hexahydrate (La(NO₃)₃·6H₂O) and thoroughly stirred to get a homogeneous solution. The FTO substrate was repeatedly sterilized in distilled water and ethanol before usage. 0.2 mol of tellurium nitrate (Te(NO₃)₄) was added and thoroughly stirred. 0.2 mol of lanthanum nitrate hexahydrate (La(NO₃)₃ · 6H₂O) was then dissolved in the solution before putting into a Teflon-lined, stainless-steel autoclave having a 100 mL capacity. The solution was maintained at 300 °C for 4 h and centrifuged at 6000 rpm. The autoclave was allowed to cool naturally to room temperature while the resulting precipitate was vacuum-dried at 70 °C for two 3 h. The prepared lanthanum erbium telluride (La_0.1Er_0.2Te_0.2) nanoparticles were annealed at different temperatures of 500, 550, and 600 °C. Following annealing each nanoparticle, a mixture of 2 mL methanol was added to the nanoparticles to ensure that the particles were blended properly. Subsequently, the film was deposited onto the FTO substrate using the Doctor Blade method (see Figure 1). Once the films were applied onto the substrates, they were allowed to dry completely before being stored for further characterization.

Figure 1. Schematic illustration of the preparation stages of lanthanum erbium telluride (La_0.1Er_0.2Te_0.2)

Characterizations

The characterization of the synthesized material was carried out for their structure., morphology, elemental, optical, and electrical properties through the use of Bruker D8 Advance X-ray diffractometer (XRD) with Cu-Kα line (λ = 1.54056 Å), MIRAS TESCAN scanning electron microscope (SEM), Energy dispersive X-ray spectroscope (EDX), 756S UV-Vis Spectrophotometer, and a Four-point probe (Model T345).

Results and discussion

UV spectroscopy study of La_0.1Er_0.2Te_0.2 nanoparticle

Figure 2 shows the UV spectroscopy of La_0.1Er_0.2Te_0.2 nanoparticles made of hydrothermal and doctor blade deposition. Figure 2 (L1) shows the absorption of light radiation of the synthesized nanomaterial decreasing with wavelength. The La_0.1Er_0.2Te_0.2 nanoparticles showed high absorbance in the visible area of the spectra with 0.648 a.u. The absorbance of the material decreased as the annealing temperature increased. The higher the annealing temperature, the lower the absorbance of the material. The unannealed nanoparticle is suitable for light-emitting systems when fabricated. It is ideal for electrodes in batteries, energy storage, solar cells and photovoltaic applications due to its low absorbance. The transmittance of La_0.1Er_0.2Te_0.2 nanoparticles in Figure 2 (L2) shows above 80% transmittance for the unannealed material and 68% for the annealed nanoparticle. The transmittance of La_0.1Er_0.2Te_0.2 nanoparticles decreased as the annealing temperature increased. The higher the annealing temperature, the lower the transmittance of La_0.1Er_0.2Te_0.2 nanoparticles. The nanoparticle had 20% reflectance in the visible region and decreased down the NIN area. However, as the annealing temperature increases, the transmittance decrease and accumulates at a wavelength above 950 nm in Figure 2 (L3). The unannealed nanoparticle has a bandgap energy of 3.50 eV in Figure 2 (L4), and the annealing nanoparticles have a bandgap of 3.27 to 2.26 eV. The higher the annealing temperature, the lower the bandgap of the material.

Structural Study

Figure 3 presents the XRD analysis of nanoparticles with a composition of La_0.1Er_0.2Te_0.2. The La_0.1Er_0.2Te_0.2 material reveals a hexagonal structure corresponding to a 2theta angle of 13.263^o. 15.375^o. 16.943^o. 18.924^o. 25.788^o. and 27.356^o for La_0.1Er_0.2Te_0.2  unannealed and 13.302^o. 15.489^o. 16.960^o. 19.055^o. 25.862^o. and 27.373^o for annealed samples. The material underwent a phase alteration upon annealing at 550^°C, resulting in a diffraction peak (111) disappearance at 15.489^o 2theta angle. The XRD pattern analysis revealed that the peaks became more distinct as the annealing temperature increased. Based on the data presented in Table 1, it is evident that there is a correlation between the annealing temperature and the crystallite size of La_0.1Er_0.2Te_0.2, with an increase in the annealing temperature increasing the size of the crystallites. Equations (1-5) [18,19], [21-27] have been used to calculate some structural characteristics, such as the full width at half maximum (FWHM), crystallite size (D), inter-planar spacing (d), lattice constants, and dislocation density.

Table 1 reveals that high temperatures increase average crystallite size with 2theta angles. The annealing temperature was likely affected by nucleation during synthesis. It has also been shown that the distances between the planes and the dislocation density alter when the angle increases. As the atomic radius of La_0.1Er_0.2Te_0.2 increases, it can be observed that the lattice constants decrease with an increase in the 2theta angle.

Figure 2. L1-absorbance, L2-transmittance, L3-reflectance, and L4-bandgap energy

Figure 3. XRD pattern of La_0.1Er_0.2Te_0.2

Table 1. La_0.1Er_0.2Te_0.2 structural properties Figure 3. XRD pattern of La_0.1Er_0.2Te_0.2

Table 2. Electrical Parameters of La_0.1Er_0.2Te_0.2

Figure 4. Resistivity and conductivity Vs thickness of the films

Figure 5. SEM of La_0.1Er_0.2Te_0.2   

Figure 6. EDXs of La_0.1Er_0.2Te_0.2

Resistivity and conductivity study of La_0.1Er_0.2Te_0.2

In Figure 4, the relationship between film thickness and both electrical resistivity and conductivity is depicted. As the thickness decreases, the electrical conductivity also decreases in Table 2. In contrast to the previous scenario, the electrical resistivity behavior is exactly the opposite. The annealing temperature decreases electrical conductivity by increasing carrier concentration. This trend allows more electric current to pass through the material, which is beneficial for optoelectronic applications.

Surface morphology of La_0.1Er_0.2Te_0.2

Figure 5 shows the surface morphologies of La_0.1Er_0.2Te_0.2. Unannealed La_0.1Er_0.2Te_0.2 had glow-like nanoparticles. As the annealing temperature rose to 500 ^oC, the glow-like nanoparticles decreased.

Conclusions

We have successfully synthesized La_0.1Er_0.2Te_0.2 nanoparticles through hydrothermal and doctor blade methods. The La_0.1Er_0.2Te_0.2 nanoparticles reveal a hexagonal structure. The XRD pattern showed that the crystallinity increased with higher annealing temperature. Unannealed La_0.1Er_0.2Te_0.2 had glow-like nanoparticles. As the annealing temperature rose to 500 ^oC, the glow-like nanoparticles decreased. Annealing temperature caused a rise in both nanoparticle clusters and surface energy. The nanoparticles became slightly prone to agglomeration due to temperature. The La_0.1Er_0.2Te_0.2 nanoparticles showed high absorbance in the visible area of the spectra with 0.648 a.u. The absorbance of the material decreased as the annealing temperature increased. The higher the annealing temperature, the lower the absorbance of the material. The unannealed nanoparticle has a bandgap energy of 3.50 eV. The annealing nanoparticles have a bandgap of 3.27 to 2.26 eV. The higher the annealing temperature, the lower the bandgap of the material. authors are grateful to the

Disclosure statement

The authors declare that they have no conflict of interest

Orcid

Imosobomeh L. Ikhioya : 0000-0002-5959-4427 

HOW TO CITE THIS ARTICLE

Haneef Shah, Shahbaz Afzal, Mohammad Usman, Kamran Shahzad, Imosobomeh L. Ikhioya *. Impact of annealing temperature on lanthanum erbium telluride (La_0.1Er_0.2Te_0.2) nanoparticles synthesized via hydrothermal approach, Adv. J. Chem. A, 2023, 6(4), 342-351.

DOI: 10.22034/AJCA.2023.407424.1386

URL: https://www.ajchem-a.com/article_177228.html