Promising lanthanide-doped BiVO4 phosphors for highly efficient upconversion luminescence and temperature sensing

Rapid detection of microalgae cells based on upconversion nanoprobes

The quantification of microalgae cells is crucial for the treatment of ships' ballast water. However, achieving rapid detection of microalgae cells remains a substantial challenge. Here, we develop a new method for rapid and effective detection of microalgae concentration by utilizing upconversion nanoprobes (UCNPs) of NaYF4:Er3+,Tm3+. Three ligands, carboxylated methoxypolyethylene glycols with 5000 and 2000 molecular weights (mPEG-COOH-5, mPEG-COOH-2) and D-gluconic acid sodium salt (DGAS), were used to convert hydrophobic UCNPs into a hydrophilic state through modification. The results show that the mPEG-COOH-5 modified UCNPs present the highest stability in an aqueous solution. Fourier Transform Infrared Spectroscopy (FTIR) measurements reveal the presence of a significant number of -COOH functional groups on UCNPs after the mPEG-COOH-5 modification. These -COOH groups enhance the hydrophilicity and biocompatibility of UCNPs. The soluble UCNPs were directly mixed with microalgae, and the upconversion luminescence (UCL) spectra of the UCNPs were recorded immediately after thorough shaking. This greatly reduces the measurement time and could realize rapid onboard detection. In this sensing procedure, the UCNPs with red UCL functioned as energy donors, while microalgae with red absorption served as an energy acceptor. The UCL gradually diminishes with an increase in microalgae concentration based on the inner filter effect, thus establishing a relationship between UCL and microalgae concentration. The accuracy of the detection is further validated through the traditional microscope counting method. These findings pave the way for a novel rapid strategy to assess microalgae concentration using UCNPs.

Large enhancement of red upconversion luminescence in beta Ba2Sc0.67Yb0.3Er0.03AlO5 phosphor via Mn2+ ions doping for thermometry

Here, this study reports single-band red upconversion emission in β-Ba2ScAlO5: Yb3+/Er3+ phosphor by doping Mn2+. The optimum concentration of Mn2+ ions in β-Ba2ScAlO5: Yb3+/Er3+ phosphor was 0.20. The intensity of red and green emissions is increased by 27.4 and 19.3 times, respectively. Compared with the samples without Mn2+ ions, the red-green integral strength ratio of β-Ba2ScAlO5: Yb3+/Er3+/Mn2+ sample was significantly increased by 28.4 times, reaching 110.9. The UCL mechanism was explored by analyzing the down-conversion luminescence spectra, absorption spectra, UCL spectra, and upconversion fluorescence lifetime decay curves of Yb3+/Er3+/Mn2+ co-doped β-Ba2ScAlO5. The enhancement of upconversion red light is achieved through energy transfer between defect bands and Er3+ ions, as well as energy transfer between Mn2+ ions and Er3+ ions. In addition, the Mn2+ doped β-Ba2ScAlO5: Yb3+/Er3+ red UCL phosphors have great potential for ambient temperature sensing in the 298-523 K temperature range. The maximum sensitivity of β-Ba2ScAlO5: Yb3+/Er3+/Mn2+ phosphor as a temperature sensor at 523 K is 0.0247 K-1.

Promising lanthanide-doped double molybdates KYb(MoO4)2 phosphors for highly efficient upconversion luminescence and temperature sensing

Here we report the highly efficient upconversion luminescence (UCL) and optical temperature sensing based on the novel host of KYb(MoO4)2 doped with trivalent lanthanide (Ln3+) ions at 980 nm excitation. The high Yb3+ concentration and unique ordered layer structure in KYb(MoO4)2 host are beneficial for the enhancement of UCL efficiency by improving the absorption and the negative migration of excitation energy. Ho3+, Er3+, and Tm3+ ions were selected to singly dope the KYb(MoO4)2 host, achieving three primary colors of red, green, blue UCL, respectively. At the optimal doping concentration, the blue upconversion quantum yield (UCQY) of the KYb(MoO4)2: 1.0%Tm3+ phosphor reaches 0.13%, which is rare for the Tm3+-doped oxides. By leveraging the efficient blue light, we achieved high-brightness white UCL by co-doping Ho3+ in KYb(MoO4)2: Tm3+. Furthermore, the temperature sensing performance of the KYb(MoO4)2: Tm3+, Ho3+ phosphors operating within the first biological window (BW-I) was evaluated based on a thermo-responsive fluorescence intensity ratio (FIR) of far-red to near-infrared (NIR) emission from completely separated 3F2,3/3H4 → 3H6 transitions of Tm3+. At the excitation of 980 nm, the maximum absolute and relative sensitivities were determined as 0.25 × 10-3 K-1 at 673 K and 2.84% K-1 at 303 K, respectively. These results indicate that the double alkali-rare-earth molybdate KYb(MoO4)2 can be used as a promising host to achieve highly efficient UCL and temperature sensing, suggesting potential applications in the fields of anti-counterfeiting, displays, and non-contact temperature sensors.

Winning color-tunable upconversion luminescence and high-sensitive optical thermometry in K3Gd(PO4)2:Yb3+,Er3+,Tm3

A series of Yb³⁺, Er³⁺, Tm³⁺ co-doped K₃Gd(PO₄)₂ are prepared via the solid-state reaction method. Upon 980 nm excitation, the synthesized samples present color-tunable upconversion luminescence ranging from yellow to blue with the increment of Tm³⁺ doping contents. The upconversion mechanisms of Yb³⁺, Er³⁺, Tm³⁺ co-doped system are systematically investigated in detail. Varying contents of Tm³⁺ can appropriately alter the upconversion emissions of blue, green and red via possible energy transfer processes. Furthermore, the thermometric performances of phosphors associated with upconversion luminescence are analyzed in the temperature region of 300-675 K. By employing non-thermally coupled energy levels (²H_11/2/⁴F_9/2 of Er³⁺), the maximum relative and absolute sensitivity reaches 0.78 % K^-1 and 0.168 K^-1. Combining the sensitivity characteristic and repeatability of thermometer, the luminescence intensity ratio technology based on non-thermally coupled energy levels may be a more effective choice for optical thermometry. These excellent results will pave an avenue to K₃Gd(PO₄)₂:Yb³⁺,Er³⁺,Tm³⁺ phosphors for the fields of color-tunable luminescence and non-contact temperature sensing.

High-sensitive temperature sensing based on thermal-enhanced emission and non-thermally coupled energy levels of white upconversion luminescence system

Na₃Y(VO₄)₂:Nd³⁺,Yb³⁺,Ho³⁺,Tm³⁺ phosphors present significantly improved sensitivity of optical temperature sensing based on thermal-enhanced upconversion luminescence and non-thermally coupled energy levels. Under 808 nm excitation, white upconversion luminescence is successfully achieved in Nd³⁺-sensitized system. In addition, the emissions intensities originated from ⁴G_5/2→⁴I_9/2 transition of Nd³⁺ and ³F_2,3→³H₆ transition of Tm³⁺ gradually increase with elevating temperature owning to the thermal population effects, as opposed to the blue (¹G₄→³H₆ transition of Tm³⁺), green (⁵S₂,⁵F₄→⁵I₈ transition of Ho³⁺) and red (⁵F₅→⁵I₈ transition of Ho³⁺) emissions intensities show continuous decreasing trend. The temperature sensing behaviors are investigated by employing multiple non-thermally coupled energy levels. Based on non-thermally coupled energy levels of ⁴G_5/2 (Nd³⁺)/¹G₄ (Tm³⁺), the absolute and relative sensitivities are obtained to be 0.433 K^-1 and 2.81 % K^-1. These results demonstrate that the Na₃Y(VO₄)₂:Nd³⁺,Yb³⁺,Ho³⁺,Tm³⁺ phosphors with superior optical thermometry performance and white luminescence within a relatively wide temperature range can achieve optical applications in many fields.

Thermal enhancing effect of upconversion luminescence in Er3+/Yb3+ co-doped Cs3BiSr(P2O7)2 phosphors

A series of Er³⁺/Yb³⁺ co-doped Cs₃BiSr(P₂O₇)₂ (CBSPO) phosphors with significant thermal enhancement were successfully prepared using the solid-state method and the thermal-enhancing effect was studied in detail. When the temperature increased from 303 to 723 K, the upconversion luminescence (UCL) emission intensities of ²H_11/2 → ⁴I_15/2 and ²H_11/2 + ⁴S_3/2 → ⁴I_15/2 of Er³⁺ in CBSPO:0.1Er³⁺/0.2Yb³⁺ were enhanced 22.81 and 10.06 times under 980 nm laser excitation, respectively. Meanwhile, the UCL color of the sample obviously changed from orange to green with the increase in temperature. Furthermore, the UCL thermal enhancement mechanism was demonstrated, which originates from phonon-assisted transitions. In addition, the maximum absolute temperature sensitivity for CBSPO:0.1Er³⁺/0.2Yb³⁺ was calculated to be 0.01026 K^-1 at 563 K via luminescence intensity ratio (LIR) technology. All the results show that the CBSPO:Er³⁺/Yb³⁺ phosphors can be used for safety warning and temperature measurement at high temperatures.

Near-infrared-emitting upconverting BiVO4 nanoprobes for in vivo fluorescent imaging

Near-infrared (NIR) emitting BiVO₄:Yb³⁺,Tm³⁺ nanoparticles are synthesized by a new solvothermal strategy using solvents of oleic acid and methanol. The obtained BiVO₄:Yb³⁺,Tm³⁺ samples show an average particle size of ≈164 nm and exhibit an asymmetry monoclinic crystal structure of BiVO₄. At NIR excitation of 980 nm, the BiVO₄:Yb³⁺,Tm³⁺ sample exhibits a nearly single NIR emission at ≈796 nm with extremely weak blue emissions from Tm³⁺ ions. These high-energy visible emissions are absorbed by the semiconducting host of BiVO₄ that possesses a bandgap of ≈2.2 eV. Therefore, the NIR excitation to a single intense NIR emission fluorescent BiVO₄ materials could be a potential ideal probe for deep-tissue high-resolution bioimaging. To validate the ability of BiVO₄ materials for bio-applications, we conduct the cytotoxicity experiments. The results show that the cytotoxicity of HeLa cells is negligible at a concentration of 0.2 mg/ml of BiVO₄:Yb³⁺,Tm³⁺ , and the cell viability approaches 90% at a high dosage of 0.5 mg/ml. The Daphnia magna and Zebrafish treated with nanoparticles (0.5 mg/ml) display bright NIR emission without any background, indicating the excellent in vivo fluorescent imaging capacity of BiVO₄:Yb³⁺,Tm³⁺ nanoparticles. Our findings offer an environment-friendly strategy to synthesize BiVO₄ UCL nanophosphors and provide a promising new class of fluorescent probes for biological applications.

Up-conversion luminescence properties and temperature sensitivity of AgBi(MoO4)2: Yb3+/Er3+/Ho3+/Tm3+ phosphors

This work begins with a study of the synthesis of multi-color luminescence phosphors, and it is followed by a discussion of the temperature sensitivity of AgBi(MoO4)2:Yb3+/Er3+. Uniform and approximately spherical...