Bi3+-Doped BaYF5:Yb,Er Upconversion Nanoparticles with Enhanced Luminescence and Application Case for X-ray Computed Tomography Imaging

ZnAl2O4:Er3+ Upconversion Nanophosphor for SPECT Imaging and Luminescence Modulation via Defect Engineering

This work reports an "all-in-one" theranostic upconversion luminescence (UCL) system having potential for both diagnostic and therapeutic applications. Despite considerable efforts in designing upconversion nanoparticles (UCNPs) for multimodal imaging and tumor therapy, there are few reports investigating dual modality SPECT/optical imaging for theranostics. Especially, research focusing on in vivo biodistribution studies of intrinsically radiolabeled UCNPs after intravenous injection is of utmost importance for the potential clinical translation of such formulations. Here, we utilized the gamma emission from 169Er and 171Er radionuclides for the demonstration of radiolabeled ZnAl2O4:171/169Er3+ as a potent agent for dual-modality SPECT/optical imaging. No uptake of radio nanoformulation was detected in the skeleton after 4 h of administration, which evidenced the robust integrity of ZnAl2O4:169/171Er3+. Combining the therapeutics using the emission of β- particulates from 169Er and 171Er will be promising for the radio-theranostic application of the synthesized ZnAl2O4:169/171Er3+ nanoformulation. Cell toxicity studies of ZnAl2O4:1%Er3+ nanoparticles were examined by an MTT assay in B16F10 mouse melanoma cell lines, which demonstrated good biocompatibility. In addition, we explored the mechanism of UCL modulation via defect engineering by Bi3+ codoping in the ZnAl2O4:Er3+ upconversion nanophosphor. The UCL color tuning was successfully achieved from the red to the green region as a function of Bi3+ codoping concentrations. Further, we tried to establish a correlation of UCL tuning with the intrinsic oxygen and cation vacancy defects as a function of Bi3+ codoping concentrations with the help of electron paramagnetic resonance (EPR) and positron annihilation lifetime spectroscopy (PALS) studies. This study contributes to building a bridge between nature of defects and UC luminescence that is crucial for the design of advanced UCNPs for theranostics.

Achieving excitation wavelength-power-dependent colorful luminescence via multiplexing of dual lanthanides in fluorine oxide particles for multilevel anticounterfeiting

The optical characteristics of multimode luminescent materials like multimode luminescence (photoluminescence, afterglow, thermoluminescence) and a multi-excitation source (light, thermal, mechanical force) play crucial roles in optical data storage and readout, document security and anticounterfeiting. A higher level of advanced anticounterfeiting may rely on multimode anticounterfeiting materials that can realize multicolor luminescence. Here, a highly integrated multimode and multicolor Y7O6F9:Er3+,Eu3+ material is developed through multiplexing of dual lanthanides in fluorine oxide particles. In photoluminescence and photoluminescence/up-conversion luminescence modes, the material Y7O6F9:Er3+,Eu3+ has the characteristic of excitation wavelength and power dependence. In the photoluminescence mode, under excitation at 254 nm and 365 nm, Y7O6F9:Er3+ and Y7O6F9:Eu3+ showed bright red and green emissions, respectively. In the photoluminescence/up-conversion mode, under the increased excitation power from 0.2 to 2.0 W cm-2, the color of luminescence emission can be finely tuned from red to orange, yellow and green. Taking this unique excitation wavelength-power-dependent luminescence property into account, a multilevel anticounterfeiting device with the Lily pattern was designed. The device readily integrates the advantages of the excitation wavelength-dependent photoluminescence emissions and excitation power-dependent photoluminescence emissions in one overall device. These findings offer unique insight for designing highly integrated multimode, multicolor luminescence materials and advanced anticounterfeiting technology toward a wide variety of applications, particularly multilevel anticounterfeiting devices.

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.

Multi-mode anti-counterfeiting guarantees from a single material CaCd2Ga2Ge3O12:Tb3+,Yb3+ - two stimuli-responsive and four-state emission

Luminescent anti-counterfeiting materials have drawn much attention in anti-counterfeiting applications due to their photochemical stability and emission patterns. However, conventional materials majorly use single-mode luminescence, leaving a growing demand for new materials to prevent counterfeiting. In this work, multi-mode anti-counterfeiting is guaranteed from a single luminescent material CaCd₂Ga₂Ge₃O₁₂:Tb³⁺,Yb³⁺via a high-temperature solid-state reaction. The experimental result showed that this single material features green luminescence with excellent photoluminescence, afterglow, thermoluminescence, and up-conversion luminescence, which are ascribed to Tb³⁺ transitions. Upon co-doping with Yb³⁺ as a sensitiser, the photo-stimuli responsiveness was achieved at 254 and 980 nm excitation sources, respectively, and the thermo-stimuli responsiveness was realised after exposure to UV of 254 nm for 10 s and heating at 45 °C, respectively. The band structure calculation, trap distribution, and effective trap depths were used to explain the luminescence mechanism. Based on the two-stimuli responsiveness and four-state emission performance, we prepared images of optical devices using silk screen printing technology. It was found that the images displayed green emission under different luminescence modes. The results prove that we successfully constructed an advanced luminescence anti-counterfeiting material.

Recent advances in lanthanide-doped up-conversion probes for theranostics

Up-conversion (or anti-Stokes) luminescence refers to the phenomenon whereby materials emit high energy, short-wavelength light upon excitation at longer wavelengths. Lanthanide-doped up-conversion nanoparticles (Ln-UCNPs) are widely used in biomedicine due to their excellent physical and chemical properties such as high penetration depth, low damage threshold and light conversion ability. Here, the latest developments in the synthesis and application of Ln-UCNPs are reviewed. First, methods used to synthesize Ln-UCNPs are introduced, and four strategies for enhancing up-conversion luminescence are analyzed, followed by an overview of the applications in phototherapy, bioimaging and biosensing. Finally, the challenges and future prospects of Ln-UCNPs are summarized.

Synthesis and upconversion emission studies of CaYF5:Ho3+/Yb3+ phosphor and its applications in optical thermometry, fingerprint detection, and security ink†

In this work, a CaYF₅:Ho³⁺/Yb³⁺ upconversion phosphor was synthesized and its structural, morphological, and optical properties were studied. The upconversion emission study was performed at an excitation pump power density of 5 W cm⁻² and emissions at 544 nm, 650 nm and 747 nm due to the ⁵F₄(⁵S₂) → ⁵I₈, ⁵F₅ → ⁵I₈ and ⁵F₄(⁵S₂) → ⁵I₇ transitions of the Ho³⁺ ion, respectively were observed. From temperature-dependent upconversion spectra temperature sensitivity was calculated and sensitivity is found to be 14 × 10⁻³ K⁻¹ for the synthesized upconversion phosphor. The photothermal conversion efficiency of the prepared sample in ethanol medium was tested. Moreover, the sample was used to develop latent fingerprints on various surfaces and good contrast in recorded images is observed. The invisible ink was prepared using the upconversion phosphor and then written words were recorded in upconversion emission mode.

In this work, a CaYF₅:Ho³⁺/Yb³⁺ upconversion phosphor was synthesized and its structural, morphological, and optical properties were studied. Apart from these studies, latent fingerprint detection and security ink applications were also demonstrated using this phosphor.

A giant enhancement in the up-conversion luminescence and high temperature sensitivity of Bi3+ doped ZnMoO4:Er3+ up-conversion phosphor

Luminescence intensity is a critical factor for upconversion (UC) oxides with high phonon energy. Herein, an effective enhancement in UC luminescence is achieved in the ZnMoO₄:Er³⁺ phosphor via Bi³⁺ doping. UV-vis-NIR diffuse reflectance spectroscopy verifies the fact that the absorption at 980 nm is enhanced by the introduction of Bi³⁺. The physical mechanism is that Bi³⁺ doping affects the transition probability between the f-levels of Er³⁺. Therefore, the green and red emission intensities are increased 82.4 and 37 times, respectively. The dependence of luminescence intensity on the power of Bi³⁺-doped ZnMoO₄:Er³⁺ combined with density functional theory (DFT) calculations also confirms the proposed energy transfer mechanism. Based on the excellent green emission, the 980 nm excited optical temperature sensing property of the synthesized sample is realized in a wide temperature range by monitoring the intensity of UC luminescence. The theoretically calculated absolute sensitivity of the optical temperature sensor was S_A = 3.04% K^-1 at 1253 K. This work paves a new way for enhancing UC luminescence and will arouse extensive interest in noncontact temperature-sensing applications.

Surface plasmon resonance of Au/Ag metals for the photoluminescence enhancement of lanthanide ion Ln3+ doped upconversion nanoparticles in bioimaging

Deep tissue penetration, chemical inertness and biocompatibility give UCNPs a competitive edge over traditional fluorescent materials like organic dyes or quantum dots. However, the low quantum efficiency of UNCPs becomes an obstacle. Among extensive methods and strategies currently used to prominently solve this concerned issue, surface plasmon resonance (SPR) of noble metals is of great use due to the agreement between the SPR peak of metals and absorption band of UCNPs. A key challenge of this match is that the structures and sizes of noble metals have significant influences on the peak of SPR formants, where achieving an explicit elucidation of relationships between the physical properties of noble metals and their SPR formants is of great importance. This review aims to clarify the mechanism of the SPR effect of noble metals on the optical performance of UCNPs. Furthermore, novel research studies in which Au, Ag or Au/Ag composites in various structures and sizes are combined with UCNPs through different synthetic methods are summarized. We provide an overview of improved photoluminescence for bioimaging exhibited by different composite nanoparticles with respect to UCNPs acting as both cores and shells, taking Au@UCNPs, Ag@UCNPs and Au/Ag@UCNPs into account. Finally, there are remaining shortcomings and latent opportunities which deserve further research. This review will provide directions for the bioimaging applications of UCNPs through the introduction of the SPR effect of noble metals.

Bioimaging with Upconversion Nanoparticles

Bioimaging enables the spatiotemporal visualization of biological processes at various scales empowered by a range of different imaging modalities and contrast agents. Upconversion nanoparticles (UCNPs) represent a distinct type of such contrast agents with the potential to transform bioimaging due to their unique optical properties and functional design flexibilities. This review explores and discusses the opportunities, challenges, and limitations that UCNPs exhibit as bioimaging probes and highlights applications with spatial dimensions ranging from the single nanoparticle level to cellular, tissue, and whole animal imaging. We further summarized recent advancements in bioimaging applications enabled by UCNPs, including super-resolution techniques and multimodal imaging methods, and provide a perspective on the future potential of UCNP-based technologies in bioimaging research and clinical translation. This review may provide a valuable resource for researchers interested in exploring and applying UCNP-based bioimaging technologies.

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.

Application of lanthanide-doped upconversion nanoparticles for cancer treatment: a review

With the excellent ability to transform near-infrared light to localized visible or UV light, thereby achieving deep tissue penetration, lanthanide ion-doped upconversion nanoparticles (UCNP) have emerged as one of the most striking nanoscale materials for more effective and safer cancer treatment. Up to now, UCNPs combined with photosensitive components have been widely used in the delivery of chemotherapy drugs, photodynamic therapy and photothermal therapy. Applications in these directions are reviewed in this article. We also highlight microenvironmental tumor monitoring and precise targeted therapies. Then we briefly summarize some new trends and the existing challenges for UCNPs. We hope this review can provide new ideas for future cancer treatment based on UCNPs.

Carambola-like Bi2Te3 superstructures with enhanced photoabsorption for highly efficient photothermal therapy in the second near-infrared biowindow

Photothermal therapy (PTT) stimulated by light in the second near-infrared (NIR-II) biowindow shows great superiorities in the penetration ability of tissue and maximum permissible exposure (MPE). Exploring new photothermal agents with good optical absorbance in the NIR-II region is highly desirable for efficient cancer therapy. Herein, we successfully prepare carambola-like bismuth telluride (Bi₂Te₃) superstructures modified with PEGylated phospholipid (Bi₂Te₃@PEG) for CT imaging-guided PTT in the NIR-II biowindow. Attributing to their superstructures, Bi₂Te₃@PEG exhibited enhanced photoabsorption with higher photothermal conversion efficiency (55.3% for 1064 nm) compared with that of Bi₂Te₃ nanoparticles. Furthermore, the good X-ray attenuation capacity of Bi endows Bi₂Te₃@PEG with an outstanding performance as computed tomography (CT) contrast agents. Bi₂Te₃@PEG superstructures have been confirmed to effectively eliminate tumor in vitro and in vivo with negligible long-term toxicities, offering them great potential to act as theranostic platforms for cancer diagnosis and treatment.

Up-conversion of lanthanide ions and down-conversion defect luminescence in BaGdF5:Yb,Er/Tm for application in anti-counterfeiting

BaGdF5:Yb,Er/Tm was prepared using a one-pot hydrothermal method, and the anti-counterfeiting patterns obtained by screen printing have dual-mode luminescence.