Sensitive Upconversion Luminescence Research Articles

Upconversion nanoparticle platform for efficient dendritic cell antigen delivery and simultaneous tracking

Upconversion nanoparticles (UCNPs) represent a group of NPs that can convert near-infrared (NIR) light into ultraviolet and visible light, thus possess deep tissue penetration power with less background fluorescence noise interference, and do not induce damage to biological tissues. Due to their unique optical properties and possibility for surface modification, UCNPs can be exploited for concomitant antigen delivery into dendritic cells (DCs) and monitoring by molecular imaging. In this study, we focus on the development of a nano-delivery platform targeting DCs for immunotherapy and simultaneous imaging. OVA 254–267 (OVA24) peptide antigen, harboring a CD8 T cell epitope, and Pam3CysSerLys4 (Pam3CSK4) adjuvant were chemically linked to the surface of UCNPs by amide condensation to stimulate DC maturation and antigen presentation. The OVA24-Pam3CSK4-UCNPs were thoroughly characterized and showed a homogeneous morphology and surface electronegativity, which promoted a good dispersion of the NPs. In vitro experiments demonstrated that OVA24-Pam3CSK4-UCNPs induced a strong immune response, including DC maturation, T cell activation, and proliferation, as well as interferon gamma (IFN-γ) production. In vivo, highly sensitive upconversion luminescence (UCL) imaging of OVA24-Pam3CSK4-UCNPs allowed tracking of UCNPs from the periphery to lymph nodes. In summary, OVA24-Pam3CSK4-UCNPs represent an effective tool for DC-based immunotherapy.Graphical abstract

Engineering of an Upconversion Luminescence Sensing Platform Based on the Competition Effect for Mercury-Ion Monitoring in Green Tea.

Accurately monitoring mercury ions (Hg2+) in food and agriculture-related matrixes (e.g., green tea) is of great significance to safeguard food safety. Here, we employed upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs) to engineer a cysteine (Cys)-assisted anti-Stokes luminescence sensing platform (UCNPs-AuNPs) for precisely detecting residual Hg2+ in green tea through the competition effect. Initially, AuNPs could effectively quench the luminescence of UCNPs through the luminescence resonance energy transfer process, which was then interrupted by Cys-triggered AuNP aggregation via Au-S, thereby restoring UCNP luminescence. Interestingly, owing to the competition effect with AuNPs toward Cys, Hg2+ could weaken the luminescence restoring efficiency, achieving a Hg2+ concentration-dependent luminescence change. On this basis, a facile, reliable, and sensitive upconversion luminescence sensing platform for monitoring residual Hg2+ in green tea was successfully established. This study offers a novel insight into integrating the competition effect and anti-Stokes luminescence for food- and agriculture-related contaminant monitoring.

Broadband Cr3+-sensitized upconversion luminescence of LiScSi2O6:Cr3+/Er3+

Broadband sensitization is an effective strategy to enhance the upconversion luminescence (UCL) of lanthanide ions. Herein, novel UC materials LiScSi2O6:Cr3+/Er3+ (LSS:Cr3+/Er3+) were synthesized by high-temperature solid state reaction and their luminescent properties were investigated. LSS:Cr3+/Er3+ has the broadband absorption in the spectral range of 600–800 nm, and meanwhile shows green UC emissions of Er3+ upon pumping Cr3+ by the 690 nm laser. The UCL of LSS:Cr3+/Er3+ belongs to the two-photon process and is attributed to the energy transfer upconversion mechanism. The effects of the Cr3+ and Er3+ concentration as well as the Yb3+ introduction were also studied. LSS:Cr3+/Yb3+/Er3+ exhibits the interesting dual-mode UCL, capable of generating the UCL of Cr3+ upon pumping Yb3+ ions and the UCL of Er3+ upon pumping Cr3+ ions. This research might promote the development of novel broadband Cr3+-sensitized UC materials.

Structure design and modulation of dual-wavelength sensitive upconversion luminescence in RE2MoO6:Er3+/Yb3+ materials

A series of RE2MoO6: 2%Er3+, 15%Yb3+ (RE = Y, Pr, Nd, Sm, Eu, Gd, Dy, and Lu) nanoparticles were prepared by citric acid-assisted sol–gel method. The upconversion luminescence (UCL) properties of block-shaped Gd2MoO6: 2%Er3+, 15%Yb3+ were the best among the materials obtained. In addition, the UCL properties of the investigated systems by two strategies could be further improved. Modulation of the crystal structure could be achieved by the substitution of rare earth ions in matrix lattice. The UC emission intensity of Gd2MoO6 doped with Y3+ (40%) was enhanced about 2.27 (2.52) more times than that of Y3+-absent samples excited at 980 nm (1550 nm). Secondly, dual wavelength was used as the excitation wavelength simultaneously: The green UCL intensity of RE2MoO6: 2%Er3+, 15%Yb3+ was almost not changed, while the red UCL intensity was enhanced compared to the sum of the red UCL intensities excited by 980 nm and 1550 nm, respectively. The UCL mechanism excited by dual wavelength was investigated in detail, in which the two co-operative excitation processes were presented.

Multifunctional NaYF4:Yb,Er@PE3@Fe3O4 nanocomposites for magnetic-field-assisted upconversion imaging guided photothermal therapy of cancer cells.

Even though various theranostic agents have been exploited for effective cancer therapy over the years, appropriate design and fabrication of theranostic agents with simple composition, convenient preparation, high theranostic efficiency and minimal side effects on non-cancer cells are still urgently needed. Herein, multifunctional NaYF4:Yb,Er@polyelectrolyte (PE3)@Fe3O4 nanocomposites, with upconversion luminescence, superparamagnetism and photothermal performance, are prepared by a layer-by-layer self-assembly technique. Compared with Fe3O4 nanoparticles (NPs), the nanocomposites exhibited nearly 2-fold strong absorption at 808 nm, and thus resulted in an enhanced near-infrared photothermal effect. With the assistance of an external magnetic field, a high sensitivity of upconversion fluorescence imaging and a low cancer cell viability of 13.9% were achieved under 808 nm laser irradiation. It is expected that multifunctional NaYF4:Yb,Er@PE3@Fe3O4 nanocomposites would pave the way toward promoting the clinical applications of theranostic nanomaterials.

Preparation of PbF2:Ho3+, Er3+, Yb3+ phosphors and its multi-wavelength sensitive upconversion luminescence mechanism

In this paper, PbF2: Ho3+, Er3+, Yb3+ phosphors are prepared by a high-temperature solid-state method. The crystal structure acquired by X ray powder diffractometer shows that the resultant phosphor is a pure cubic PbF2 crystal. The upconversion (UC) emission spectra of samples are performed by a fluorescence spectrophotometer coupled with lasers of 980 nm, 1064 nm and 1550 nm, presenting the green emission in the range of 541∼548 nm and red emission in the range of 653–667 nm, corresponding to the excitation path: Ho3+: 4F9/2→4I15/2, Er3+: 4S3/2→4I15/2, Er3+: 4F9/2→4I15/2 and Ho3+: 5F5→5I8. Finally, the UC luminescence mechanism is analyzed under excitation of different wavelengths. The result shows that the phosphors have a promising prospect for application in anti-counterfeiting technologies and solar cell field.

Enhanced dual-wavelength sensitive upconversion luminescence of BiPO4:Yb3+/Er3+ phosphors by Sc3+ doping

A series of BiPO4:Yb3+/Er3+ samples with different concentrations of Sc3+ ions were prepared by two different methods: one is solvothermal synthesis process and subsequent calcination route, and the other is solid-state reaction method. On one hand, hexagonal and monoclinic phases of BiPO4:Yb3+/Er3+ were successfully obtained by the above two synthesis methods, respectively, and the UC luminescence intensity depended a lot on the crystalline phases. On the other hand, the dual-wavelength sensitive UC emission properties of BiPO4:Yb3+/Er3+/Sc3+ were firstly investigated. It was found the UC emission intensity was significantly enhanced by introducing appropriate Sc3+ ions to the system whether under excitation at 980 nm or 1550 nm. Moreover, the UC emission mechanisms under the excitation at 980 as well as 1550 nm were also proposed on the base of experimental results.

Preparation of Gd2O2S:Er3+,Yb3+ phosphor and its multi-wavelength sensitive upconversion luminescence mechanism

Er3+–Yb3+ codoped Gd2O2S infrared upconversion phosphor has been prepared via a coprecipitation–solid state reaction process.

Active-core/active-shell nanostructured design: an effective strategy to enhance Nd3+/Yb3+ cascade sensitized upconversion luminescence in lanthanide-doped nanoparticles

Giant enhancement of Nd3+–Yb3+ cascade sensitized upconversion luminescence has been achieved in lanthanide-doped active-core/active-shell nanoparticles.

Broadband Cr^3+-sensitized upconversion luminescence in La_3Ga_5GeO_14: Cr^3+,Yb^3+,Er^3+

Broadband-light-sensitized upconversion (UC) photon management phenomenon in La3Ga5GeO14:Cr3+,Yb3+,Er3+ is reported, featuring the concentrated broadband noncoherent light excitable at room temperature. Energy transfer among Cr3+/Yb3+/Er3+ in the Stokes and UC luminescence processes reveals that Yb3+ as a “bridge” is requisite for Cr3+-sensitized UC luminescence of Er3+. Low Cr3+ contents are preferred for UC luminescence of Yb3+-Er3+, since it would be quenched by high Cr3+ contents. The designed UC emissions 2H11/2→4I15/2 and 4S3/2→4I15/2 of Er3+ at around 510 ~560 nm are proposed to through Energy transfer upconversion (ETU) mechanism based on the Cr3+-Yb3+ dimer model with superexchange interaction according to crystallographic data and the decay curves of Er3+ UC emission. This research may open up a new perspective to design novel photonic materials excitable by broadband noncoherent light for improving the photoresponse of solar cells.

Influence of the Nd 3+ ions content on the FTIR and the visible up-conversion luminescence properties of nano-structure BaTiO 3, prepared by sol–gel technique

The nano-structure BaTiO 3 (BT) powder doped with different concentrations of Nd 3+ ions were annealed at 750 °C for 1 h to form nano-structure tetragonal phase of BT powder. The structure properties studied using XRD and FTIR methods. Sensitized up-conversion luminescence observed under excitation of 808 nm diode laser, suggesting that the Nd 3+ ions-doped BT might be an ideal up-conversion material for infrared excitation. The influence of increasing the concentration of the Nd 3+ ions on the luminescence intensity investigated using laser diode. The up-conversion mechanisms in the doped system will be discussed by analyzing the energy level structures of the Nd 3+ ions.

Anomalous power dependence of sensitized upconversion luminescence

The expected excitation power dependencies for any upconversion emission band of an acceptor ion is investigated theoretically when the excitation takes place on a sensitizer ion and subsequent energy transfer upconversion from the sensitizer to the acceptor ion is exclusively responsible for the excitation of the acceptor ion. Under these limitations it is shown that emission from a state that requires $k$ energy transfer upconversion steps will have a slope of $k$ in the low-power regime when the luminescence intensity is plotted in a double-logarithmic representation versus absorbed pump intensity. In the high-power regime, any emission band will show a slope of 1, irrespective of the number of energy transfer steps from the sensitizer to the acceptor ions that are involved. The theoretical results are verified experimentally by data on three different inorganic systems with different types of sensitizer and acceptor ions: rare earth (RE) ions as well as transition metal (TM) ions. The active ions in the systems that are studied experimentally are RE/RE, RE/TM, and TM/TM, where the first dopant indicates the sensitizer ion and the second dopant indicates the upconverting ion. These different classes of sensitizer and upconverter ions all agree with the theoretical predictions put forward by the model. Thus providing confidence in the applicability (within the boundary conditions put forward here) of the model described.

Sensitized up-conversion luminescence of Ho3+ in Nd3+-Yb3+-Ho3+ co-doped ZrF4-based glass

Up-conversion processes for the blue, green and red emissions were found two-photon phenomenon, known as the cooperative phenomenon. This phenomenon was assisted by Nd3+ → Yb3+ → Ho3+ energy transfer. The strong green emission due to the Ho3+ : (5F4, 5S2)→ 5I8 transitions was observed in Nd3+-Ho3+ co-doped ZrF4-based fluoride glasses under 800 nm excitation. As an attempt to enhance Ho3+ up-conversion luminescences in the Nd3+ – Ho3+ co-doped ZrF4-based glasses, Yb3+ ions were added to the glasses. As a result it was found that, in 800 nm excitation of 60 ZrF4. 30BaF2. (8-x)LaF3. lNdF3. xYbF3. 1HoF3 glasses (x=0 to 7), sensitized up-conversion luminescences are observed at around 490 nm (blue), 545 nm (green), and 650 nm (red), which correspond to the Ho3+ : 5F3 → 5I8, ( 5F4, 5S2)→5I8 and 5F5→ 5I8 transitions respectively. The intensities of the green and red emissions in a 3 mol % YbF3-containing glass were about 50 times stronger than those glasses without YbF3. This is based on sensitization due to Yb3+ ions. In particular, the green emission was extremely strong and the Nd3+-Yb3+-Ho3+ co-doped ZrF4-based glasses have a high possibility of realizing a green up-conversion laser glass. In this paper the up-conversion mechanism in the glasses is discussed in detail.