​Synthesis of silicate clay minerals-based novel Mt/YF3:Eu3+ nanocomposites for regulated luminescent intensity-quantum yield-fluorescence lifetime

Author links open overlay panelHongxia Peng【彭红霞】 a,Weicai Peng a,Jingyou jiang a,Huibin Shi a,Juan Zhu a,Junna Xu a,Fabiao Yu 【于法标】b c

• a

• Hunan Provincial Key Laboratory of Fine Ceramics and Powder Materials, Hunan University of Humanities, Science and Technology, Lou’di, Hunan, 417000, PR China

• b

• Key Laboratory of Hainan Trauma and Disaster Rescue, The First Affiliated Hospital of Hainan Medical University, Hainan Medical University, Haikou, 571199, China

• c

• Engineering Research Center for Hainan Bio-Smart Materials and Bio-Medical Devices, Key Laboratory of Emergency and Trauma, Ministry of Education, Key Laboratory of Hainan Functional Materials and Molecular Imaging, College of Emergency and Trauma, Hainan Medical University, Haikou, 571199, China

Received 28 June 2023, Revised 6 August 2023, Accepted 10 August 2023, Available online 11 August 2023, Version of Record 25 September 2023.

Handling Editor: Dr P. Vincenzini

https://doi.org/10.1016/j.ceramint.2023.08.115

Abstract

Rare earth luminescent materials have broad application prospects in the fields of white light LED lighting, flat panel display, biological imaging and so on. Here, we developed a novel silicate clay minerals-based montmorillonite nanosheet(Mt)/YF3:Eu3+ nanocomposites with strong luminescence performance. Mt carrier plays a three role: (1) reducing the size and improving dispersion of YF3: Eu3+ nanoparticles by surface effect; (2) narrowing down the band gap and increasing Urbach tail energy by interface effect; (3) reducing the shielding of the hole-electron Coulomb interactions while improving the exciton binding energy of YF3:Eu3+, thus improving the radiative recombination by dielectric effect. Therefore, orthogonal phase YF3: Eu3+ nanoparticles (diameter 20∼140 nm) binding to the surface of Mt via chemical bond interactions. The combination of Mt and YF3:Eu3+ not only enhanced luminescent intensity (about 2 times) but also improved the quantum yield (0.14% to 0.4%) and fluorescence lifetime (0.338 ns to 0.405 ns) of YF3:Eu3+ nanoparticles at 595 nm. In addition, the combination of Mt and YF3:Eu3+ give luminescent properties to Mt thereby improving the utilization rate of Mt and YF3: Eu3+ nanoparticles. It was found that the research supplies an insight on the development of new type luminescent materials, and hopefully it could promote them application in many fields.

1. Introduction

Rare earth phosphors for white light LED have several remarkable advantages such as narrow band emission, which can be concentrated in a specific wavelength range, good stability at short ultraviolet (185 nm) radiation, and high emission intensity at high temperature. Among, YF3: Eu3+ is a superior red phosphor due to its low refractive index, good chemical stability, non-hygroscopicity and insoluble [1,2]. However, it has many disadvantages, for instance, shorter fluorescence lifetime, lower fluorescence quantum yield and utilization rate [3].

For the moment, the usual methods to improve the luminescence property of rare earth luminescent materials mainly include coating method, ion doping method and introducing surface plasma resonance effect method, but these methods still have many different defects. Coating method is effective method to improve the luminescence properties of rare-earth luminescent materials. By coating a homogeneous or heterogeneous shell on the surface of the material to reduce the surface defects of the material, increase the distance of the luminescence center, and reduce the surface fluorescence quenching to improve its luminescence intensity [[4], [5], [6], [7], [8]]. However, almost all the coating methods face a common problem, which is difficult to effectively control the thickness. Ion doped method is another effective method to improve the luminescence properties of rare-earth luminescent materials. The local symmetry of matrix lattice is adjusted by ion doping (e. g., Fe3+) to improve the emission intensity of the rare-earth luminescent materials. However, it's hard to control accurately the content of doping elements and the replacement position of target atoms. And the coexistence of multiple doped ions with high concentration will cause cross-relaxation, which can lead to fluorescence quenching. In addition, the emission intensity of rare-earth luminescent materials can be enhanced by coupling resonance energy transfer with surface plasmon materials, such as gold and silver, WO3-x and Cu2-xSe [[9], [10], [11], [12]]. However, the price of gold and silver is higher, and the morphology and defect concentration of WO3-x and Cu2-xSe are difficult to control [13]. Al2O3 and SiO2 nanoparticles, as commonly used dielectric materials, can improved the luminescence intensity of the rare earth fluoride luminescent materials [14,15]. However, they have lower dielectric constant ratio with the nano-materials due to their charge transfer and rotation, it is difficult to efficient enhancement of the surface and internal local fields of the rare earth fluoride luminescent materials. And the dielectric constant of Al2O3 and SiO2 nanoparticles can only be controlled by changing them porous structure. At the same time, the porous structure and its void size not easy to control, which limits their practical application in the field of optical materials. Montmorillonite (Mt, Al2O9Si3, dielectric constant 16.1–38.2) nano-sheet is a class of negatively charged silicate sheets of nanothickness [16,17]. Mt nano-sheet is a kind of sheet-like silicate clay mineral with mortal specific surface area, up to 700–800 m2/g [18]. The interface interaction of the Mt nano-sheet and loaded materials can not only change the electronic structures, exciton binding energy and band gaps of the loaded materials, but also effectively adjusts the size, morphology and dispersion of the loaded materials [[19], [20], [21], [22], [23]]. Its high dielectric constant ratio are adjusted by the concentration of the loaded materials. Mt is natural formation, extensive resources, complete shape, low price and low toxicity. Mt is a good silicate clay minerals assembly of nano-functional materials. For exemple, a new type of CeO2 @MMT nanoenzyme-targeted therapeutic drug was successfully synthesized. Cerium oxide nanoparticles (CeO2 NPs) were grown in situ on montmorillonite (MMT) for inflammatory sites. By binding to MMT, CeO2 NPs significantly inhibited the absorption phenomenon in the whole body, reduced its potential nanotoxicity, and also give photodynamic activity to MMT [24]. A new nanocomposite composed of nanostructured minerals (Montmorillonite), starch particles and liquid metals was reported. The new nanocomposites have chemical, optical and mechanical response property. They has write-wipe capabilities in electrical filed, and also enhance microbial culture/biofilm growth in vitro and biofuel production [25]. Guan et al. designed and synthesized a unique fluorescent surfactant, which combines the properties of the aggregation-induced emission (AIE) and amphiphilicity, to image macrodispersion of montmorillonite (Mt) and layered double hydroxide fillers in polymer matrix. The proposed fluorescence imaging provides a number of important advantages over electron microscope imaging, and opens a new avenue in the development of direct three-dimensional observation of inorganic filler macrodispersion in organic–inorganic composites [26].

We combined the beneficial properties of Mt nanosheet and YF3: Eu3+ to synthesize a new type of silicate clay minerals-based Mt/YF3: Eu3+ nanocomposites (Fig. 1). A combination of Mt nanosheet and YF3: Eu3+ not only endows Mt with luminescent properties but also effectively improves the luminescent performance of YF3: Eu3+ nanoparticles by regulate their size, exciton binding energy and band gaps. This research render a new policy for improving the utilization rate and optimizing performance of Mt nanosheet and YF3: Eu3+ nanoparticles.

1. Fig. 1 Synthesis procedure and schematic illustration of luminescence enhancement mechanism of Mt/YF3: Eu3+ nanocomposites.
   

Fig. 2. XRD patterns of Mt, YF3:Eu3+ and Mt/YF3:Eu3+ nanocomposites.

Fig. 3. SEM of Mt (a, b), Mt/YF3:Eu3+ and (inset) corresponding particle size distribution histogram (c, d), YF3:Eu3+ (e, f).

Fig. 4. (a) TEM image of Mt/YF3:Eu3+ nanocomposite; (b) HRTEM image and the SAED pattern of Mt/YF3:Eu3+ nanocomposite; (c–i) Energy Dispersive X-ray (EDX) mapping of Mt/YF3:Eu3+ nanocomposite.

Fig. 5. Infrared spectrum of Mt, YF3:Eu3+ and Mt/YF3:Eu3+ nanocomposite.

Fig. 6. XPS spectra (A) XPS survey spectra of Mt, YF3:Eu3+ and Mt/YF3:Eu3+ nanocomposite and High-resolution Si 2p (B), Al 2p (C), Mg 1s (D), Eu 3d (E), Y 3d (F), O 1s (G), F 1s (H).

Fig. 7. Fluorescence spectra of Mt/YF3:Eu3+ nanocomposites: Excitation (A) and emission (B) spectra of Mt/YF3:Eu3+ and YF3: Eu3+.

Fig. 8. Fluorescent decay curves of 5D0-7F2 (595 nm) for Eu3+.

Fig. 9. (A) UV–vis spectra of Mt, Mt/YF3:Eu3+ and YF3:Eu3+ nanocomposite; (B–D) DRS spectra of YF3:Eu3+, Mt/YF3:Eu3+and Mt nanocomposite with the corresponding plots of [F(R∞)hv]2 versus hv.

Fig. 10. Urbach tail energy fitting of YF3:Eu3+ and Mt/YF3:Eu3+ nanocomposite.

Fig. 11Dielectric performance of YF3:Eu3+ and Mt/YF3:Eu3+; (A) dielectric constant and (B) tan δ