Preparation and luminescent properties of rare earth Eu-doped nano-ZnO composite films on textiles

Abstract

This study reports the successful preparation of rare-earth Eu-doped ZnO composite films on cotton fabric, achieving remarkable luminescent properties through the magnetron sputtering method. A comprehensive analysis of the structural and luminescent characteristics of the samples was conducted using various evaluation techniques, including scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FT-IR), UV absorption spectroscopy, photoluminescence spectroscopy, photocatalysis testing and color fastness measurements. The findings indicate that the affiliation of Eu³⁺ ions significantly enhanced the luminescent intensity along with the photocatalytic property of the ZnO-loaded fabrics. Furthermore, the sample sputtered for a duration of 1 hour exhibited superior overall optical performance than that of 3 hours. This study demonstrates the potential of Eu-doped ZnO composite films for various applications, including luminescent and photocatalytic textiles.

Keywords

Luminescent textile magnetron sputtering rare earth doping photocatalysis cotton fabric

Introduction

Luminescent textiles, which emit visible light under specific excitation conditions, have attracted significant attention in material science. Their applications span diverse fields, from decorative fabrics to safety wear in dark environment.^1–3 However, current luminescent textiles often suffer from limited brightness, durability as well as radioactivity and toxicity,⁴ hindering their widespread use. Addressing these limitations is crucial for the advancement of luminescent textiles and their integration into various practical applications. One way to address these limitations is to explore the use of non-toxic and bright luminescent materials that can be incorporated into textiles.

ZnO is a widely used semiconductor with excellent optical and electrical properties.^5,6 ZnO-based luminescent materials have gained significant attention due to their inexpensive, non-toxic and efficient nature,⁷ as well as the wide range of applications in optoelectronics⁸ and potential for integration into textiles.^9,10 By themselves, ZnO nanomaterials, in particular, offer high luminescence efficiency and stability.¹¹ Nevertheless, ZnO luminescent materials still face challenges such as insufficient photocatalytic activity¹² and intensity.¹³ However, embedding rare earth elements, which are known for their unique optical properties, into ZnO matrices has been proposed as a potential solution to these issues.^14,15

The incorporation of rare earth elements, such as europium (Eu), into ZnO-based luminescent materials offers significant improvements.^16,17 Europium’s unique electronic structure enables efficient energy transfer and emission of specific wavelengths, leading to enhanced luminescence intensity.¹⁸ Previous studies have demonstrated that Eu-doped ZnO nanocomposites exhibit superior luminescent properties compared to undoped ZnO and ZnO doped with low concentration of Eu.^5,19,20 These improvements are attributed to the energy level transitions within the Eu ions, which facilitate efficient energy transfer and emission processes.²¹

However, most of the current studies that combine europium with ZnO are focused on the composite in the forms of powders, solutions or membranes. In addition, rare earth luminescent textiles are usually prepared through methods like melt spinning, solution spinning, surface coating or bonding methods. Magnetron sputtering technology, a versatile method for thin film deposition, offers significant advantages in our study. Its ability to precisely control the composition and microstructure of deposited films benefits the creation of uniform and high-quality Eu-doped ZnO composite films on textiles.²² Furthermore, magnetron sputtering allows for the deposition of thin films with excellent adhesion to the textile substrate, ensuring durability and stability.^23,24 By utilizing this technology, we aim to overcome the limitations of current luminescent textiles and develop a novel material with superior luminescent properties suitable for a wide range of applications.^25,26

Experimental

Materials

The materials used in this work include cotton woven fabric (90.66 g/m², Xinzhe Textile Industry), zinc (Zn) target (Ф 76.2 × 3 mm, 99.995%, Zhongnuo New Material (Beijing) Technology Co., LTD) and europium oxide-doped zinc oxide target that possess compositions of ZnO:Eu₂O₃ at a ratio of 97:3 atomic percent (Ф 76.2 × 3 mm, 99.99%, Zhongnuo New Material (Beijing) Technology Co., LTD) as well as anhydrous ethanol (Sinopharm Chemical Reagent Co., Ltd).

Preparation of rare earth Eu-doped nano ZnO composite film

The radio-frequency magnetron sputtering method was employed to deposit thin films onto cotton fabrics with ZnO:Eu₂O₃ target or Zn target. The study utilized Zn for reaction sputtering to form ZnO film on the fabric due to the fact that Zn targets are more robust and solid, with higher deposition rate and no oxygen deficiency issue.

Multiple cotton fabrics measuring 20 × 20 cm were cut and soaked in anhydrous ethanol for 30 min. Subsequently, they were placed in an oven at 50°C for 30 min to assure complete evaporation of the ethanol. This step aimed to eliminate any impurities or sizing agents on the cotton fabrics that could potentially influence the final experimental results.²⁷

The treated fabrics were then fixed onto a sample holder positioned 15 cm away from the target. Under certain conditions (argon gas flow rate = 20 mL/min, base vacuum = 1.5 × 10⁻³ Pa, working pressure = 0.5 Pa, sputtering duration = 1 h/3 h), differentiated ZnO:Eu³⁺/ZnO thin films were deposited onto the cotton fabrics by adjusting the sputtering power and the targets. In the following paper, fabric sputtered with Zn target for 1 h is named as ZnO 1, fabric sputtered with 3% Eu₂O₃:ZnO target for 1 h and 3 h are named as ZnO:Eu³⁺ 1 and ZnO:Eu³⁺ 3, respectively. All physical properties and spectroscopic measurements were performed using a single replicate to reduce batch to batch variations.

Structural characterization

Scanning electron microscopy (SEM)

SEM (TM4000Plus, Hitachi Corporation, Japan) was used to observe the micro-morphological characterization of cotton fabric surface prior and after coating. It was achieved by scanning the sample (0.5 × 0.5 cm) with a high-energy electron beam (acceleration voltage = 15 kV, magnification = ×4000). Prior to scanning, the sputtered sample was securely affixed to the sample stage using electron microscope tape, followed by a gold spraying process to enhance the conductivity and image quality.²⁸

Fourier transform infrared spectroscopy (FTIR)

The chemical bonds within the samples (0.5 × 0.5 cm) were meticulously examined using the IS50 Fourier transform infrared spectrometer manufactured by Thermo Fisher Scientific Co., Ltd. Since various molecular structures absorb infrared light in distinct patterns, the infrared spectrum can be applied as a reliable indicator for identifying the type of chemical bond present in a compound. Through this method, it was able to qualitatively assess the chemical substances within the coated fabrics.²⁹

Optical tests

UV absorption

The UV absorption spectroscopy analysis of the samples (∼2.6 cm in diameter) was performed by applying a calibrated double beam UV-Vis spectrophotometer (TU-1901, Beijing Puyang General Instrument Co., LTD). The experimental fabric was placed in the spectrophotometer for scanning (λ = 350-800 nm). The spectrophotometer measures the transmitted light intensity at various wavelengths, generating a UV absorption spectrum. This spectrum displayed the fabric’s absorption characteristics as a function of wavelength, allowing for the identification of any absorption peaks or troughs that might indicate the presence of specific chemical species.³⁰

Photoluminescence

Upon exposure to short-wavelength light, objects store energy and emit long-wavelength light, known as fluorescence.³¹ Changes in fluorescence intensity across different wavelengths are reflected in the excitation spectrum while the emission spectrum characterizes the intensity and distribution of fluorescence. Emission spectra (E_X = 350 nm, λ = 370–600 nm) of the samples (2.5 × 2.5 cm) were detected using a F-7100 spectrophotometer.

Photocatalysis

A UV-visible spectrophotometer was applied to evaluate the photocatalytic activity of the fabrics, thereby verifying the ability of the prepared luminescent textiles to degrade formaldehyde in the air under solar irradiation. Immersing in 10 mL of methylene blue (MB) solution, the samples (∼4 cm in diameter) were continuously irradiated for 6 h under a metal halide lamp (light gray matte). The absorbance changes of solution (λ = 554 nm) were measured every 30 min using a UV-visible spectrophotometer. As the concentration of MB solution at this wavelength being proportionate to its absorbance, by calculating the degradation rate of the MB solution and comparing the data at different time points, a photocatalytic degradation curve was plotted to visually demonstrate the degradation process.

In the degradation curves, the illumination time (t) was plotted with -ln (C/C₀), and the pseudo-first-order degradation rate constant is represented by the slope k of the linear fit. Degradation rate = (C₀ - C) / C × 100%, where C₀ is the initial concentration of MB and C is the concentration of MB after illumination of n × 30 min (n = 1, 2, 3…, 7).

Color fastness

Color fastness to rubbing

Textiles encounter frequent friction in daily use, such as the friction among fabrics as well as between fabrics and our skin, necessitating favorable color fastness to rubbing to prevent color changes and coating transfer. To assess this property, referring to the GB/T 3920-2008 standard, samples (15 × 5 cm) were rubbed repeatedly under controlled conditions on a Y(B)571-II pre-set rubbing tester, and their color retention was visually evaluated employing a gray scale card ranging from one to five to quantify color fastness where higher grades indicate superior adhesion between the membrane and fabric, resulting in reduced membrane transfer and longer textile lifespan.

Color fastness to soaping

Soap fastness measures a fabric’s resistance to color fading when washed with soapy water on SW-12AII washing fastness tester which is graded on a scale of five levels using a gray scale card according to GB/T 3921-2008. For nano ZnO:Eu³⁺ doped thin-film fabrics (15 × 5 cm), soap fastness reflects the film’s adhesion to the substrate and reveals the fabric’s structural color, luminescence, and photocatalysis. Samples were cut, sewn with white cloth and washed in soapy water on a heat-collecting stirrer. After drying, their fading and staining levels were observed.

Results and discussion

Structural characterization

Scanning electron microscopy (SEM)

In Figure 1(a), the scanning electron microscopy (SEM) image of the untreated cotton fabric at ×5 k magnification clearly revealed the microstructure of the cotton fiber, exhibiting a smooth and flat surface. In contrast, Figure 1(b) displayed the ZnO-doped fabric, which exhibited a dense, uniform distribution of ZnO particles on the surface. Figure 1(c) and (d) demonstrate that the ZnO:Eu³⁺-doped fibers exhibit a more angular ridge structure compared to the original fibers, with particle aggregations evident on the fabric surface, corresponding to the formation of ZnO:Eu³⁺ composite films. Additionally, the fabric sputtered with ZnO:Eu₂O₃ targets for 3 h exhibits a rougher surface compared to that sputtered for 1 hour, as anticipated. Collectively, these observations indicate the successful coating of films onto the cotton fabric via the radio-frequency magnetron sputtering technique.

Figure 1.

SEM images (magnification ×5000) of original cotton fabric (a), ZnO 1 (b), ZnO:Eu³⁺ 1 (c) and ZnO:Eu³⁺ 3 (d).

Fourier transform infrared spectroscopy (FTIR)

The FTIR peaks and spectrum serve as a unique fingerprint for a particular molecular structure and its chemical bonding patterns, thereby facilitating the identification of a molecule’s fundamental backbone along with its associated functional groups.³²

As seen in Figure 2, a prominent characteristic peak at 1096 cm⁻¹ was observed, indicating the presence of Eu-O bonds.³³ Furthermore, the absorption in the range of 400-600 cm⁻¹ primarily revealed the stretching vibrations of Zn-O and Eu-O, reflecting the vibrational modes of these bonds (the Zn-O symmetric stretch is typically at 443 cm-1; Eu₂O₃ shows characteristic vibration modes at 446 cm⁻¹ and 586 cm⁻¹).^34,35 Additionally, the appearance of characteristic peaks at 720 cm⁻¹ suggested a potential association with the cellulose component in the cotton fiber.³⁶ This comprehensive FTIR analysis aligns with the anticipated chemical composition and vibrational characteristics of the samples, providing validation of our experimental observations.

Figure 2.

FTIR spectra of fabrics coated with ZnO:Eu³⁺ (sputtering time = 1 h or 3 h) and ZnO (sputtering time = 1 h).

Optical properties tests

UV absorption

The UV-visible absorption spectra of three fabric samples coated with ZnO 1, ZnO:Eu³⁺ 1 and ZnO:Eu³⁺ 3 are presented in Figure 3. All samples exhibited a characteristic ZnO absorbance peak at ∼360 nm.³⁷ A comparative analysis revealed that the UV absorbance peak at ∼350 nm decreased significantly in the ZnO:Eu³⁺ sample sputtered for 1 h compared to the ZnO sample sputtered for the same duration. This attenuation was further exacerbated in the ZnO:Eu³⁺ sample sputtered for 3 h. This effect mainly contributes to the increase in the thickness of the coated fabric, causing reduction in transmittance of UV light/may be attributed to variations in particle sizes of ZnO caused by the differentiated nucleation and condensation process in different samples.³⁸

Figure 3.

UV-visible spectra of fabrics coated with ZnO:Eu³⁺ (sputtering time = 1 h or 3 h) and ZnO (sputtering time = 1 h).

Moreover, the ZnO:Eu³⁺ sample sputtered for 3 h exhibited a broadened absorbance peak compared to the other two samples, accompanied by an observable red shift. The possible reason is that the increased internal stress within the film resulting from the extended sputtering time of 3 h likely altered the band structure and enhanced the overlap of electron wave functions, ultimately leading to a broadened band gap.³⁹These findings suggest that the embedding of the rare earth metal Eu and the prolongation of sputtering time negatively impact the fabric’s ultraviolet absorption capability.

Photoluminescence

To identify the luminescence performance of ZnO:Eu³⁺ coated fabrics, the photo fluorescence spectra with an excitation wavelength of 350 nm are plotted in Figure 4. Emission peaks at 400-550 nm were presented in all three samples, which is contributed to the intrinsic defect emission of ZnO host.¹⁸ It can be seen that the introduction of Eu barely effected the position of the luminescent peak since no emission from the Eu³⁺ in ZnO:Eu³⁺ could be observed under an excitation wavelength lower than 385 nm²¹, though distinctive changes in intensity were exhibited in the spectra.

Figure 4.

PL spectra of fabrics coated with ZnO:Eu³⁺ (sputtering time = 1 h or 3 h) and ZnO (sputtering time = 1 h).

As expected, a significant enhancement in intensity was observed by incorporating Eu into the system when comparing ZnO and ZnO:Eu³⁺ samples that were sputtered for a same time period of 1 h. However, after extending the sputtering time to 3 h, the PL intensity of ZnO:Eu³⁺ sample dropped dramatically which is likely due to the inhibition of luminescence property caused by growth in the thickness of the prepared film/ can be understood by the reduction of the energy transfer due to the non-radiation processes in ZnO.⁴⁰

Photocatalysis

The photocatalysis of treated fabrics was studied over its capability of degrading MB as shown in Figure 5. Under ultraviolet irradiation, ZnO produces electron-hole pairs that react with water and oxygen to generate free radicals with strong oxidizing property, which can react with methylene blue molecules to break their chemical bonds, and thus degrade them into small molecules. The absorbance of MB visually decreased with the presence of all three samples under illumination, illustrating the degradation of MB is positively correlated with illumination time, indicating the potential use of the materials for degrading formaldehyde in the air for purification purpose.

Figure 5.

Relationship between -ln(C/C₀) and illumination time of fabrics coated with ZnO:Eu³⁺ (sputtering time = 1 h or 3 h) and ZnO (sputtering time = 1 h).

Drawn from the linear fitting results, the degradation rate constants of fabrics coated with ZnO (sputtering time = 1 h), ZnO:Eu³⁺ (sputtering time = 1 h) and ZnO:Eu³⁺ (sputtering time = 3 h) were 0.124, 0.187, and 0.211, respectively. Fabrics coated with ZnO:Eu³⁺ resulted in effective degradation of MB of up to 55%–56% after 3.5 h of illumination while ZnO coated fabric exhibited a milder degradation rate of 42%, which corresponds with what was revealed by previous studies^41,42 where the addition of Eu can enhance the photocatalytic property of ZnO under visible light irradiation. As a result, it can be concluded that the fabrics coated with ZnO:Eu³⁺ exhibited the faster and higher photocatalytic degradation rate.

Color fastness

Extensive color fastness tests were conducted through soaping and rubbing protocols to thoroughly investigate the durability of ZnO:Eu³⁺ loaded cotton fabrics. Encouragingly, all three fabrics achieved a color fastness grade of five following a standard soaping procedure, which aligns with the grades stipulated for infant textiles according to the Chinese National Standard GB 18,401-2010. Additionally, the fabrics exhibited moderate color fastness after rubbing for both warp and weft directions, scoring grades of 2-3. Notably, the dry crock fastness tended to be slightly more favorable compared to the wet crock fastness. Crucially, ZnO:Eu³⁺ coated fabrics demonstrated a consistently higher overall color fastness level. It is therefore concluded that the adhesion of Eu³⁺ ions favorably contributed to the enhanced color fastness of the treated cotton fabrics, however, further exploration is still needed on improving its color fastness to rubbing Table 1.

Table 1.

Color fastness results of the samples.

Sample	Color fastness to soaping				Color fastness to rubbing
	Warp direction		Weft direction		Warp direction		Weft direction
	Discoloration	Staining	Discoloration	Staining	dry crock fastness	wet crock fastness	dry crock fastness	wet crock fastness
ZnO 1	5	5	5	5	2-3	2	2-3	2
ZnO:Eu³⁺1	5	5	5	5	3	2	3	2-3
ZnO:Eu³⁺3	5	5	5	5	3	2-3	2-3	2-3

Conclusions

The study successfully prepared rare earth Eu-doped nano-ZnO composite films on textiles, comprehensively analyzed their structural and luminescent properties. To the best of our knowledge, this represents the first time that Eu-doped ZnO with a substrate as textile through magnetron sputtering for luminescent and photocatalytic applications. SEM observations confirmed the uniform deposition of ZnO:Eu³⁺ films on cotton fabric, and FTIR spectra validated the characteristic Zn-O/Eu-O bonds. ZnO:Eu³⁺ samples exhibited decreased UV absorption with longer sputtering, while the 1 h-sputtered sample displayed significantly enhanced photoluminescence. The ZnO:Eu³⁺ coated fabrics more effectively degraded MB up to 56% after 3.5 hours of illumination. Samples achieved high color fastness grades while further improvements are necessary to improve their resistance to rubbing. Collectively, these findings demonstrate the successful preparation of luminescent and photocatalytic-active Eu-doped ZnO films on textiles, with the 1 h sputtered sample exhibiting optimal overall properties, opening avenues for further studies and potential diverse applications.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Fujian Natural Science Foundation Project; 2023J011405 and 2024J011179.

ORCID iDs

Xiaohong Yuan

Qufu Wei

References

Xuefeng

Jingfang

Mingqiao

. Design, Development, and application of luminescent Knitted fabrics. Knitting Industries 2015; 10: 4.

Hui'e

Jun

. Application of luminescent materials in stage Costumes. Journal of Jiangnan University (Natural Science Edition) 2009; 4: 1.

Yanna

. Study on the structure and properties of luminescent fibers. Jiangnan University, 2008.

Jing

Junhong

Zhongjun

. Application and development status of luminescent textiles. China Fiber Inspection 2013; 19: 3.

Huang

Yin

Zheng

. Applications of ZnO in organic and hybrid solar cells. Energy Environ Sci 2011; 4(10): 3861–3877.

Sun

Lam

Sham

, et al. Synthesis and synchrotron light-induced luminescence of ZnO nanostructures: Nanowires, nanoneedles, nanoflowers, and tubular whiskers. J Phys Chem B 2005; 109(8): 3120–3125.

Samadi

Zirak

Naseri

, et al. Recent progress on doped ZnO nanostructures for visible-light photocatalysis. Thin Solid Films 2016; 605: 2–19.

Jain

MMMKVP

. Effect of N Ion implantation on structural, optical properties and dielectric behavior of ZnO thin-films. In 2023 IEEE 13th International Conference Nanomaterials: Applications & Properties (NAP). Bratislava, Slovakia, 2023.

Manna

Begum

Kumar

, et al. Enabling Antibacterial coating via Bioinspired Mineralization of nanostructured ZnO on fabrics under Mild conditions. ACS Appl Mater Interfaces. 2013; 5(10): 4457–4463.

10.

Liu

, et al. Construction of cellulose based ZnO nanocomposite films with Antibacterial properties through one-step coagulation. ACS Appl Mater Interfaces 2015; 7(4): 2597–2606.

11.

Theerthagiri

Salla

Senthil

, et al. A review on ZnO nanostructured materials: energy, environmental and biological applications. Nanotechnology 2019; 30(39): 392001.

12.

Manna

Goswami

Shilpa

, et al. Biomimetic method to Assemble nanostructured Ag@ZnO on cotton fabrics: Application as self-cleaning flexible materials with visible-light photocatalysis and antibacterial activities. ACS Appl Mater Interfaces 2015; 7(15): 8076–8082.

13.

Jian

Chen

Wang

, et al. Enhancement in photoluminescence performance of carbon-decorated T-ZnO. Nanotechnology. 2015; (26).

14.

Junling Feng

FenZhang

, et al. Investigation of 4f-Related electronic transitions of rare-earth doped ZnO luminescent materials: Insights from first-principles calculations. ChemPhysChem: A European journal of chemical physics and physical chemistry 2020; 21(1): 4.

15.

Anwar

Kayani

Hassan

, et al. Enhancement in photocatalytic activity and biological properties of Sm doped ZnO nanostructures by the increase in Sm contents. Inorg Chem Commun 2023; 158: 111431.

16.

Atkinson

. Crystal structures and phase transitions in the rare earth oxides. University of Salford, 2014.

17.

Korake

Kadam

Garadkar

. Photocatalytic activity of Eu3+-doped ZnO nanorods synthesized via microwave assisted technique. J Rare Earths. 2014; 32(4): 306–313.

18.

Mingya

Guiye

Yajun

, et al. Guorui. Synthesis and luminescence properties of Eu3+-doped ZnO nanocrystals by a hydrothermal process. Mater Chem Phys. 2007; 106(2–3): 305–309.

19.

Aneesh

Jayaraj

. Red luminescence from hydrothermally synthesized Eu-doped ZnO nanoparticles under visible excitation. Bull Mater Sci 2010; 33(3): 227–231.

20.

Yang

Lang

, et al. Synthesis and optical properties of Eu-doped ZnO nanosheets by hydrothermal method. Mater Sci Semicond Process 2011; 14(3-4): 247–252.

21.

Ishizumi

Kanemitsu

. Structural and luminescence properties of Eu-doped ZnO nanorods fabricated by a microemulsion method. Appl Phys Lett 2005; 86(25): 253103–253106.

22.

. Analysis on the optical characteristics of ZnO thin film prepared by magnetron sputtering, 2015, pp. 1143–1147.

23.

Rossnagel

Hopwood

. Magnetron sputter deposition with high levels of metal ionization. Appl Phys Lett 1993; 63(24): 3285–3287.

24.

Saidu

Sanpei

Wakaki

, et al. Morphological characterization of RF magnetron sputtered zinc oxide thin films-laser assisted. JSAP Annual Meetings Extended Abstracts 2019; 1: 1855.

25.

Purbayanto

Nurfani

Naradipa

, et al. Enhancement in green luminescence of ZnO nanorods grown by dc-unbalanced magnetron sputtering at room temperature. Opt Mater 2020; 108: 110418.

26.

Tan

Liu

Niu

, et al. Materials recent progress in magnetron sputtering technology used on fabrics. Materials. 2018; 11(10).

27.

Danqing

Yadong

Yong

, et al. Study on technology of ethanol dehydration by pervaporation processing. Chem Ind Eng Prog 2012.

28.

Majeed

Siraj

Naseem

, et al. Structural and optical properties of gold-incorporated diamond-like carbon thin films deposited by RF magnetron sputtering. Mater Res Express 2017; 4(7): 076403.

29.

Lei

Tong

Huaqiang

. Luminescent mechanism and application of rare earth luminescent materials. Metallurgical Management 2019; 000(007): 25.

30.

Winiberg

FAF

Chao

Caravan

, et al. A white cell based broadband transient UV-vis absorption spectroscopy with pulsed laser photolysis reactors for chemical kinetics under variable temperatures and pressures. Rev Sci Instrum 2023; 94(11): 114103.

31.

Drummen

GPC

. Fluorescent Probes and fluorescence (microscopy) techniques - Illuminating biological and biomedical research. Molecules 2012; 17(12): 14067–14090.

32.

Asep

BDN

Risti

Fiandini

. Interpretation of fourier transform infrared spectra (FTIR): a practical approach in the polymer/plastic thermal decomposition. Indonesian Journal of Science and Technology 2022; 8(1): 113–126.

33.

Sun

. Photoluminescence investigation of Eu2+-doped BaSO4. Experimental and Theoretical Nanotechnology 2023: 387–394.

34.

Chandrasekhar

Nagabhushana

Sharma

, et al. Particle size, morphology and color tunable ZnO:Eu3+ nanophosphors via plant latex mediated green combustion synthesis. J Alloys Compd 2014; 584(1): 417–424.

35.

Zhao

Guo

, et al. Preparation and characterization of Graphene/europium oxide composites. Mater Manuf Process 2012; 27(5): 494–498.

36.

Abidi

Cabrales

Haigler

. Changes in the cell wall and cellulose content of developing cotton fibers investigated by FTIR spectroscopy. Carbohydr Polym 2014; 100(2): 9–16.

37.

Prasanth

Vugt

LKV

Vanmaekelbergh

DAM

, et al. Resonance enhancement of optical second harmonic generation in a ZnO nanowire. Appl Phys Lett 2006; 88(18): 512.

38.

Huang

Liu

, et al. Preparation and optical investigation of europium-doped zinc oxide nanocrystals. Laser & Infrared. 2003; 33.

39.

Jing

Huawa

. Effect of deposition temperature on structure and optical properties of ZnO films. J Shaanxi Univ Sci Technol Nat Sci Ed 2007; 25(6): 4.

40.

Huang

Liu

Gao

, et al. Synthesis and optical properties of Eu3+ doped ZnO nanoparticles used for white light emitting diodes. J Nanosci Nanotechnol 2014; 14(4): 3052–3055.

41.

Alam

Khan

Ali

, et al. Comparative photocatalytic activity of sol–gel derived rare earth metal (La, Nd, Sm and Dy)-doped ZnO photocatalysts for degradation of dyes. RSC Adv 2018; 8(31): 17582–17594.

42.

Sin

Lam

Lee

, et al. Preparation of rare earth-doped ZnO hierarchical micro/nanospheres and their enhanced photocatalytic activity under visible light irradiation. Ceram Int 2014; 40(4): 5431–5440.