Sm Nanocrystals Research Articles

Photoinduced electron transfer in Eu2+ and Sm3+ co-doped CaF2 nanocrystals prepared by co-precipitation

We report on the photoinduced electron transfer in Eu2+ and Sm3+ co-doped CaF2 nanocrystals prepared by a facile co-precipitation method using CaCl2, EuCl2, SmCl3 and NH4F. The doping of divalent Eu2+ was realized by employing granular zinc in the CaCl2/EuCl2 solution under nitrogen to reduce Eu3+→ Eu2+. The CaF2:xEu,0.2%Sm nanocrystals were prepared with different Eu concentrations of x = 0, 0.2, 0.5, 1.5, and 2.5%, resulting in an average crystallite size between 54 and 36 ± 1 nm. The maximum luminescence intensities of Eu2+ and Sm2+ were obtained for the x = 0.5% sample. Photoinduced electron transfer and back transfer in the CaF2:0.5%Eu,0.2%Sm nanocrystals were measured by detecting the Eu2+ and Sm2+ luminescence, upon exposure to 340 and 310 nm UV LED light. Interestingly, the photoionization of Eu2+ occurred 6 times faster for the sample co-doped with 0.2% Sm. Upon exposure to 340 nm light, a reduction and increase of the Eu2+ and the Sm2+ luminescence were observed, respectively. Subsequent exposure to 310 nm light decreased the Sm2+ luminescence, but the luminescence of Eu2+ kept on being bleached, albeit at a lower rate. Whilst the Sm valence state could be reversibly changed between the trivalent and divalent state by 340 and 310 nm light, the observation that the Eu2+ luminescence did not recover may indicate that a third centre is involved in the photoinduced electron transfer mechanisms.

CdTe nanocrystals doped with Sm3+: blueshift and enhanced emission

This work used an aqueous-phase method to prepare Sm-doped CdTe nanocrystals (NCs). The successful doping of Sm into the CdTe lattice was confirmed by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), as well as UV–Visible (UV–Vis) absorption and emission spectroscopies. The CdTe and CdTe:Sm NCs are monodispersed as uniform spherical nanocrystals with cubic structures. The particle diameters are ∼4.2, ∼3.3, and ∼2.6 nm for CdTe, CdTe:Sm(5%) and CdTe:Sm(10%) NCs, respectively. Compared with pure CdTe, the CdTe:Sm(5%) NCs exhibit a blueshift of 9–23 nm in their absorption bands and a blueshift of 8–17 nm in their emission bands. With increasing concentration of Sm3+, the quantum yield (QY) of the CdTe:Sm NCs increases initially and then decreases. The CdTe:Sm NCs have longer fluorescence lifetimes than CdTe, probably due to the introduction of trap states. Due to charge compensation, the CdTe:Sm NCs have much stronger emission peaks.

Suppression of low temperature magnetic ordering in samarium nanoparticles

The role of finite size effects on magnetic order has been investigated in samarium nanoparticles prepared by physical vapor deposition. A dense layer composed of distinct nanoparticles with a mean particle diameter of 26 nm was deposited on a diamagnetic substrate. M(T) measurements identify the expected pair of antiferromagnetic ordering temperatures in the bulk Sm precursor, at 113 K and 14 K, where the magnetic unit cell for the lower ordering temperature is 10.36 nm along the c-axis. The high temperature ordering of the hexagonal sites in the Sm nanocrystals is slightly decreased with respect to that of bulk Sm, while the low temperature transition associated with the cubic sites is significantly suppressed. The observed changes are attributed to finite size effects, with ordering suppressed as the particle radius approaches the length of the magnetic unit cell, and surface moments become more prominent.

Synthesis, characterization and optical studies on Sm2+-doped CdSe nanocrystals: a blueshift and fixed emission with high quantum yields

CdSe:Sm nanocrystals (NCs) were synthesized by a water phase method, and their structures, shapes and optical properties were further characterized. X-ray diffraction (XRD) analysis suggested that both the CdSe and CdSe:Sm NCs contained (111), (220) and (311) lattice planes in the zinc blende structure overlapped with the (002), (110) and (112) lattice planes in the wurtzite structure, and the diameters were about 4.2, 3.3 and 2.3 nm for CdSe, CdSe:Sm(8%) and CdSe:Sm(10%) NCs, respectively. All of the CdSe:Sm NCs were monodispersed and uniform spherical nanocrystals. The CdSe:Sm(10%) NCs prepared with different reaction times exhibited constant absorption spectra at 430 nm and a fixed emission peak at 581 nm. Compared with those of pure CdSe NCs, the fluorescence emission of CdSe:Sm(10%) NCs blueshifted 20–36 nm, and the absorption peak initially redshifted and then blueshifted with the prolongation of reaction time. In addition, the Sm2+ doping decreased the fluorescence lifetime and increased the quantum yields (QYs) of CdSe NCs. The QYs of CdSe:Sm NCs increased initially and then decreased with the increase in the amount of doped Sm2+. The initial pH and charge compensator concentration also exhibited significantly enhanced fluorescence emission of CdSe:Sm NCs. CdSe and CdSe:Sm NCs were prepared via a water phase method. The structure and optical properties were investigated; the Sm2+ was doped into CdSe NCs successfully. CdSe and CdSe:Sm NCs all exhibit nearly spherical particles, doping Sm2+ increases the particle size, and the QYs are also enhanced. As the reaction time varies to 1, 2, 5, 8 and 10 h, the emission spectra of CdSe NCs present redshift, while the CdSe:Sm NCs have a fixed emission peak, which is the characteristic peak of Sm2+. As compared with pure CdSe NCs, the emission spectra of CdSe:Sm NCs appear blueshift by 20–36 nm. Doping Sm2+ into CdSe NCs can improve the optical properties.

Highly efficient valence state switching of samarium in BaFCl:Sm nanocrystals in the deep UV for multilevel optical data storage

We report on the highly efficient generation of stable Sm2+ in nanocrystalline BaFCl:Sm3+ by exposure in the deep UV (UV-C) below 250 nm. The generated Sm2+ can be read out via its distinct fluorescence signature which is efficiently excited around 425 nm by the relatively strong f-d transitions with e ≈400 (l mol−1 cm−1). The generation of Sm2+ can also be reversed, erasing the fluorescence signal via two-photon ionization by increasing the power at 425 nm from ≤ 1 mW/cm2 to ~100 mW/cm2. It follows that the switching mechanism is based on oxygen impurities that are in close proximity to the Sm3+ ions. The photoionization kinetics indicate that the average Sm3+- oxide impurity separation is a few interionic spacings. The level of Sm3+- Sm2+ conversion in BaFCl is shown to be tunable over a large dynamic range, and therefore could serve as a platform for rewritable ultra-high density multi-level optical data storage. The present study also sheds light on BaFCl:Sm3+ as a photoluminescent X-ray storage phosphor.

Optical properties and Judd–Ofelt analysis of Sm ions in Lanthanum trifluoride nanocrystals

LaF3:samarium (Sm) nanocrystals have been prepared by hydrothermal method. The nanocrystals were characterized by X-ray diffraction, transmission electron microscopy. The absorption, luminescence spectra of LaF3:Sm samples were measured at room temperature. By using Judd–Ofelt theory, intensity parameters (Ω2, Ω4 and Ω6) have been obtained from optical absorption measurements. Based on these Judd–Ofelt parameters, various radiative parameters such as radiative transition probabilities, radiative lifetime, branching ratios and stimulated emission cross-section for 4G5/2 excited level of LaF3:Sm nanocrystals were predicted.

Water‐Soluble, Monodisperse, Lanthanide‐Doped Y(Gd)VO4 Nanocrystals as Promising Multimodal Bioprobe

AbstractMonodisperse and water‐soluble lanthanide (Ln3+)‐doped Y(Gd)VO4 nanocrystals (NCs) have been successfully synthesized by a fast, facile, and environmentally friendly microwave‐assisted route with poly(acrylic acid) as the surfactant. The Y(Gd)VO4:5 %Ln3+ (Ln = Eu, Dy, Sm) NCs have unique fluorescence properties and polydimethylsiloxane (PDMS)‐based white solid nanocomposites containing YVO4:5 %Eu3+ NCs show red emission upon UV irradiation. GdVO4 NCs can act as CT and MRI contrast agents as a result of their magnetic and X‐ray absorption properties. A layer of SiO2 was coated onto the surfaces of the nanoparticles and MTT assays were carried out to test the cytotoxicity of the YVO4@SiO2 and GdVO4 NCs. The results indicate that the Y(Gd)VO4 NCs have potential in multimodal optical/MRI/CT bio‐imaging.

Luminescence of Long-Term Ordered Pure and Doped Gallium Phosphide

Evolution of luminescence is reported from GaP crystals that were grown over 40 years ago. This is the longest running cycle of experiments to study the temporal effects of crystal lattice and impurity ordering. The results clearly indicate impurity ordering and the formation of a new type of crystal lattice in which periodically disposed impurities modify and improve properties of the crystal. A high-density exciton system bound to a nitrogen impurity superlattice and GaP:N, GaP:N:Sm nanocrystals distributed in transparent fluorine-containing polymers will be used as the base elements for a new generation of optoelectronic devices.

Optical properties of Sm-doped ZnS nanocrystals

In order to understand the spectral characteristics of ZnS : Sm nanocrystals, in which a novel optical memory effect has been observed, optical properties have been studied between 2 and 300 K for the samples prepared by a solution method. The broad fluorescence and excitation bands observed in the visible region are tentatively assigned to the transitions between the 4f 6 and 4f 55d states of Sm 2+ and also to the transitions of excitons bound to Sm 2+. Temperature dependence of the intensity of the lowest-energy emission band and the dependence of its peak position on the excitation wavelength have been explained well by these assignments.