Doped LaF3 Nanocrystals Research Articles

Enhanced and tuneable green and red emissions in RE3+ doped LaF3 nanocrystals

RE3+ (Ce3+, Gd3+, Tb3+, Eu3+)-doped LaF3 silica nano-glass-ceramics (nGCs) were obtained by thermal treatment of precursor sol-gel glasses. The precipitation and distribution of spherical LaF3 nanocrystals (NCs) with sizes around 8.5 nm in the silica matrix were confirmed by X-ray diffraction patterns, transmission electron microscope images and energy dispersive X-ray spectroscopy measurements. Very efficient energy transfer mechanisms from Ce3+ to Tb3+ or Eu3+ ions, mediated by Gd3+ ions through the Ce3+→(Gd3+)n→(Tb3+/Eu3+) scheme, were observed in Ce3+-Gd3+-Tb3+ and Ce3+-Gd3+-Eu3+ co-doped nGCs, yielding intense green and red emissions, respectively. Moreover, simultaneous and tuneable Ce3+ sensitized Tb3+ and Eu3+ emissions were obtained in Ce3+-Gd3+-Tb3+-Eu3+ co-doped nGCs by varying the content of Tb3+ and Eu3+ ions, and the corresponding energy transfer mechanisms were analysed. Results suggest these nGCs as potential UV to VIS converters in the field of lighting and display.

Visible transparent white light emitting ink from a Ce3+ sensitized monodispersed Tb,Sm co-doped LaF3@C-dot nanocomposite.

Bright white light emission (CIE values 0.32 and 0.33) has been achieved by a single excitation source (254 nm) from a monodispersed nanocomposite composed of Ce3+, Tb3+ and Sm3+ doped LaF3 nanocrystals (NCs) and N-doped C-dots where Ce3+ acts as an excellent sensitizer. Controlled deposition of the C-dots onto the surface of the LaF3 NCs impedes conventional aggregation induced quenching (AIQ) of the C-dots in solid state. The transparent colloidal ink was coated onto an UV chip to fabricate a white light emitting diode (WLED) with a luminous efficacy of 8.72 lm W-1.

Radiative transition dynamics of holmium ions-doped LaF3 nanocrystals

Ho3+-doped LaF3 nanocrystals with 1.0, 3.0, and 5.0 mol% Ho3+ have been prepared by hydrothermal method. The nanocrystals possess hexagonal structure with $$P\stackrel{-}{3}c1$$ space group with lattice parameters a = 7.172 ± 0.002 A and c = 7.342 ± 0.002 A. The room temperature absorption, luminescence spectra of LaF3:Ho3+ was investigated in detail. Judd–Ofelt theory has been applied to estimate $${{\Omega }}_{{\uplambda }}$$ (λ = 2, 4, 6) intensity parameters. For LaF3:5%Ho3+ sample, $${\varOmega }_{2}=1.872\times {10}^{-20}{\text{cm}}^{2},$$ $${\varOmega }_{4}=4.006\times {10}^{-20}{\text{cm}}^{2}$$ and $${\varOmega }_{6}=4.720\times {10}^{-20}{\text{cm}}^{2}.$$ Based on these Judd–Ofelt parameters, various radiative parameters such as radiative transition probabilities $${ A}_{R},$$ radiative lifetime $${ \tau }_{R},$$ branching ratios $${\beta }_{R}$$ and stimulated emission cross-section $${\sigma }_{em}\left({\lambda }_{p}\right)$$ for various emission levels of LaF3:5%Ho3+ sample have been determined. It is found that the luminescence quantum efficiency of 5F5 excited state is decreased from 55.8 to 37.9% with increasing Ho3+ concentration from 1 to 5 mol%.

Retraction: Self-limited growth of Pr3+-doped LaF3 nanocrystals in oxyfluoride glass and glass-ceramics

Retraction of ‘Self-limited growth of Pr3+-doped LaF3 nanocrystals in oxyfluoride glass and glass-ceramics’ Biswajit Pal et al., RSC Adv., 2017, 7, 14824–14831.

Physical Background for Luminescence Thermometry Sensors Based on Pr3+:LaF3 Crystalline Particles

The main goal of this study was creating multifunctional nanoparticles based on rare-earth doped LaF3 nanocrystals, which can be used as fluorescence thermal sensors operating over the 80–320 K temperature range including physiological temperature range (10–50°C). The Pr3+:LaF3 (CPr = 1%) microcrystalline powder and the Pr3+:LaF3 (CPr = 12%, 20%) nanoparticles were studied. It was proved that all the samples were capable of thermal sensing into the temperature range from 80 to 320 K. It was revealed that the mechanisms of temperature sensitivity for the microcrystalline powder and the nanoparticles are different. In the powder, the 3P1 and 3P0 states of Pr3+ ion share their electronic populations according to the Boltzmann and thermalization of the 3P1 state takes place. In the nanoparticles, two temperature dependent mechanisms were suggested: energy migration within 3P0 state in the temperature range from 80 K to 200 K followed by quenching of 3P0 state by OH groups at higher temperatures. The values of the relative sensitivities for the Pr3+:LaF3 (CPr = 1%) microcrystalline powder and the Pr3+:LaF3 (CPr = 12%, 20%) nanoparticles into the physiological temperature range (at 45°C) were 1, 0.5, and 0.3% °C−1, respectively.

The upconversion luminescence and magnetism in Yb3+/Ho3+ co-doped LaF3 nanocrystals for potential bimodal imaging

Biocompatible upconversion nanoparticles with multifunctional properties can serve as potential nanoprobes for multimodal imaging. Herein, we report an upconversion nanocrystal based on lanthanum fluoride which is developed to address the imaging modalities, upconversion luminescence imaging and magnetic resonance imaging (MRI). Lanthanide ions (Yb3+ and Ho3+) doped LaF3 nanocrystals (LaF3 Yb3+/Ho3+) are fabricated through a rapid microwave-assisted synthesis. The hexagonal phase LaF3 nanocrystals exhibit nearly spherical morphology with average diameter of 9.8 nm. The inductively coupled plasma mass spectrometry (ICP-MS) analysis estimated the doping concentration of Yb3+ and Ho3+ as 3.99 and 0.41%, respectively. The nanocrystals show upconversion luminescence when irradiated with near-infrared (NIR) photons of wavelength 980 nm. The emission spectrum consists of bands centred at 542, 645 and 658 nm. The stronger green emission at 542 nm and the weak red emissions at 645 and 658 nm are assigned to 5S2 → 5I8 and 5F5 → 5I8 transitions of Ho3+, respectively. The pump power dependence of luminescence intensity confirmed the two-photon upconversion process. The nanocrystals exhibit paramagnetism due to the presence of lanthanide ion dopant Ho3+ and the magnetization is 19.81 emu/g at room temperature. The nanocrystals exhibit a longitudinal relaxivity (r 1) of 0.12 s−1 mM−1 and transverse relaxivity (r 2) of 28.18 s−1 mM−1, which makes the system suitable for developing T2 MRI contrast agents based on holmium. The LaF3 Yb3+/Ho3+ nanocrystals are surface modified by PEGylation to improve biocompatibility and enhance further functionalisation. The PEGylated nanocrystals are found to be non-toxic up to 50 μg/mL for 48 h of incubation, which is confirmed by the MTT assay as well as morphological studies in HeLa cells. The upconversion luminescence and magnetism together with biocompatibility enables the adaptability of the present system as a nanoprobe for potential bimodal imaging.

PH-dependent morphology and its effect on the optical properties of LaF3:Nd nanocrystals

Nd3+-doped LaF3 nanocrystals with different morphologies have been produced via solvothermal method at various pH values (1–6). Their morphologies and optical properties were characterized by TEM, fluorescence spectra and decay curves. A possible formation mechanism including burst-nucleation and growth process was proposed. The results reveal that when the pH increases from 1 to 2 to 4–6, the nanocrystals' mean size reduces slightly and the morphologies transform from the hollow sphere to the packed hexagon. The fluorescence lifetime and quantum efficiency achieved maximum for the samples synthesized at pH = 2. These nanocrystals with small size (<30 nm) and bright photoluminescence are promising phosphors in the applications of biological, optical amplifiers and liquid laser fields.

Photoluminescence and Energy Transfer Between Sm &amp;lt;sup&amp;gt;3+&amp;lt;/sup&amp;gt; Ions in LaF&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; Nanocrystals Prepared by Hydrothermal Method

The aim of this research is to study photoluminescent properties and particularly energy transfer between Sm3+ ions in LaF3 nanocrystals because the energy transfer process has a significant effect on the luminescence efficiency and lifetime. Sm3+-doped LaF3 nanocrystals with 0.1, 0.2, 0.3, 1.0, 2.0, 3.0, 4.0 and 5.0 mol% Sm3+ have been prepared by hydrothermal method. The obtained nanocrystals were characterized by X-ray diffraction, transmission electron microscopy, photoluminescence and luminescence decay measurement. The results showed that the LaF3:Sm3+ nanocrystals possess hexagonal structure with <img width="29" height="16" src="http://article.sciencepublishinggroup.com/journal/123/1231229/image001.png" /> space group. The room temperature photoluminescence and photoluminescence excitation spectra of LaF3:Sm3+ were investigated in detail and interpreted by optical intra-configurational f–f transitions within Sm3+ ions. When Sm3+ ion concentration in the nanocrystals is increased, the excitation energy is transferred from the “bulk” Sm3+ ions to the surface Sm3+ ions followed by non-radiative recombination at centers at the surface of the nanocrystals. The photoluminescence decay curves of 593 nm peak in the LaF3 nanocrystals doped with 1.0-5.0 mol% Sm3+ were best fitted to the Inokuti-Hirayama model with the dominant dipole-quadrupole interaction (S = 8). The values of fitting parameters for the energy transfer process were determined.

用于液体激光介质的Nd3+离子掺杂氟化镧纳米颗粒的制备与性能表征

用于液体激光介质的Nd³⁺离子掺杂氟化镧纳米颗粒的制备与性能表征

Mild molten-salt synthesis and photoluminescence property of LaF3 and its white-light emission with Eu doping

Mild molten salt synthesis (MSS) method was utilized to synthesize rare earth fluorides nanocrystals with favorable fluorescence efficiency. LaF3 nanocrystals were achieved through this modified MSS method by only using La(NO3)3·6H2O and NH4HF2 as starting materials. NH4HF2 is difunctionality as both fluorine source and the flux. The effects of reaction time and temperature to the synthesis of LaF3 nanocrystals were discussed in detail. The fluorescence of LaF3 nanocrystals was detected with excitation wavelength of 360nm, the results showed a broad band emission centered at 475nm. The photoluminescence properties of pure LaF3 nanocrystals and Eu3+ doped samples were also investigated. In our work, white light emission was achieved in single element (Eu3+) doped LaF3 nanocrystals by adjusting the concentration of Eu3+ ions. This would be the combination of broad emission of LaF3 nanocrystals and sharp line emission of Eu3+ in the LaF3:Eu3+ nanocrystals.

Rapid Microwave Synthesis and Fluorescence of LaF&lt;sub&gt;3&lt;/sub&gt; and LaF&lt;sub&gt;3&lt;/sub&gt;:Re (Re=Ce&lt;sup&gt;3+&lt;/sup&gt;, Eu&lt;sup&gt;3+&lt;/sup&gt;, Tb&lt;sup&gt;3+&lt;/sup&gt;) Nanocrystals

LaF3 and LaF3: Re (Re= Ce3+, Eu3+ and Tb3+) nanocrystals have been successfully synthesized by a facile and rapid microwave heating method. The structure, morphology and fluorescent properties of the as-prepared products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence spectroscopy (PL). XRD patterns showed that the undoped and doped LaF3 nanocrystals had hexagonal structure with good crystallinity and high purity. TEM and HRTEM images showed that the LaF3 nanocrystals have uniform sizes with mean diameter about 20 nm and are characteristic of inner cavities. The luminescence spectra of the LaF3: Re (Re= Ce3+, Eu3+ and Tb3+) nanocrystals indicated that different rare-earth ions have been successfully doped in LaF3 matrix via the microwave heating method.

Luminescence properties of Nd3+-doped LaF3 nanocrystals with a long lifetime in organic solvents

A kind of monodisperse LaF3:Nd nanocrystal with a small size and long lifetime in solvent was synthesized via a hydrothermal process. The crystalline phase, morphology, and luminescence properties were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), emission spectroscopy as well as dynamic decays. The results indicated that LaF3:Nd nanocrystals with a size below 30 nm have great dispersity in various solvents. An excellent lifetime of 359 μs was detected in a transparent DMSO–tetrabromoethane dispersion. It suggested that these nanocrystals could have great applications in biological and optical amplification fields.

Size-dependence of LaF3:Eu3+ nanocrystals on Eu3+ photo-luminescence intensity

Size-dependence of Eu3+-doped LaF3 nanocrystals on the 5D0-7FJ photoluminescence intensity was investigated, where LaF3:Eu3+ nanocrystals were prepared through a hydrothermal route with a cationic surfactant cetyltrimethylammonium bromide (CTAB) as size-controlled agent and by post-annealing at an appropriate temperature at N2 atmosphere. It was found that LaF3:Eu3+ obtained was in hexagonal structure with space group P3c1 and had good crystalinity. When LaF3:Eu3+ nanocrystals were synthesized with 0.006 mol/L CTAB the average particle size was maximized to be 25.4 nm and the luminescence intensity was 1.5 times higher than that prepared without CTAB or with more CTAB concentration. The mechanism of the particle growth was also discussed in this paper.

Infrared-to-visible and infrared-to-violet upconversion fluorescence of rare earth doped LaF3 nanocrystals

This paper reports that hexagonal-phase LaF3:Yb0.203+, Er0.023+ and LaF3:Yb0.203+, Tm0.023+ nanocrystals (NCs) were synthesized via a hydrothermal method. The transmission electron microscopy, selected area electron diffraction, powder x-ray diffraction, and thermogravimetric analysis are used to characterize the NCs. Under 980 nm excitation, the Yb3+/Er3+ and Yb3+/Tm3+ codoped NCs colloidal solutions present bright green and blue upconversion fluorescence, respectively. These NCs show efficient infrared-to-violet and infrared-to-visible upconversion. The upconversion fluorescence mechanisms of La F3:Yb0.023+ Er0.023+ and LaF3:Yb0.023+, Tm0.023+ NCs are investigated with a 980-nm diode laser as excitation source.

Synthesis of LaF3 nanocrystals by laser-induced Nd3+ atom heat processing in oxyfluoride glasses

Oxyfluoride glasses with the compositions of 33SiO2–21Al2O3–33NaF–9LaF3–4Nd2O3–xErF3 (mol%), x=0 and 0.5, are prepared using a conventional melt-quenching technique, and the laser-induced crystallization method using continuous-wave (cw) diode lasers with a wavelength of λ=795nm is applied to form LaF3 crystals on the glass surface. It is found from X-ray diffraction analyses and micro-photoluminescence spectra that Nd3+-, Er3+-doped LaF3 crystals with a diameter of ∼23nm are patterned by laser irradiations with a laser power of 1.8W and a laser scanning speed of 10μm/s. It is proposed that the lines patterned by laser irradiations are consisted of the composite of Nd3+-doped LaF3 nanocrystals and the SiO2-based oxide glassy phase. It is suggested that the combination of cw diode laser (λ=795nm) irradiations and the non-radiated relaxation process in the f–f transition level of 4F5/2→4I9/2 of Nd3+ ions is effective in the spatially selected local patterning of fluoride crystals in oxyfluoride glasses with Nd3+ ions.

Ionic Liquid-Based “All-in-One” Synthesis and Photoluminescence Properties of Lanthanide Fluorides

A facile route to the synthesis of LnF3 nanocrystals has been accomplished in three ionic liquids (ILs) (OmimPF6, OmimBF4, and BmimPF6). The partial hydrolysis of PF6− and BF4− was utilized to introduce a new fluoride source. Uniform LnF3 (Ln = La, Ce, Pr, Nd, Sm, Eu, Er), Tb3+-doped CeF3, and Eu3+-doped LaF3 nanocrystals could be obtained in a large scale, and the products were up to 0.15 g per 10 mL solvents. In the “all-in-one” systems, the ILs acted as solvents, reaction agents, and templates. The effects of cosolvents, cationic and anionic parts of the ILs on the nanocrystals morphologies, and sizes were studied. The optical properties of the nanocrystals synthesized in different ILs were discussed. The simple and large-scale synthesis of these unique luminescent inorganic nanocrystals will find great potential applications in biolabels, light-emitting diodes (LEDs), and redox luminescent switches.