Near-infrared Persistent Luminescence Research Articles

Enabling Visible-Light-Charged Near-Infrared Persistent Luminescence in Organics by Intermolecular Charge Transfer.

Visible light is a universal and user-friendly excitation source; however, its use to generate persistent luminescence (PersL) in materials remains a huge challenge. Herein, we apply the concept of intermolecular charge transfer (xCT) in typical host-guest molecular systems, which allows for a much lower energy requirement for charge separation, thus enabling efficient charging of near-infrared (NIR) PersL in organics by visible light (425-700nm). Importantly, NIR PersL in organics occurs via the trapping of electrons from charge-transfer aggregates (CTAs) into constructed trap states with trap depths of 0.63-1.17eV, followed by the detrapping of these electrons by thermal stimulation, resulting in a unique light-storage effect and long-lasting emission up to 4.6h at room temperature. The xCT absorption range was modulated by changing the electron-donating ability of a series of acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile-based CTAs, and the organic PersL was tuned from 681 to 722nm. This study on xCT interaction-induced NIR PersL in organic materials provides a major step forward in understanding the underlying luminescence mechanism of organic semiconductors and these findings are expected to promote their applications in optoelectronics, energy storage, and medical diagnosis. This article is protected by copyright. All rights reserved.

Persistent Luminescence Lifetime-Based Near-Infrared Nanoplatform via Deep Learning for High-Fidelity Biosensing of Hypochlorite.

In light of deep tissue penetration and ultralow background, near-infrared (NIR) persistent luminescence (PersL) bioprobes have become powerful tools for bioapplications. However, the inhomogeneous signal attenuation may significantly limit its application for precise biosensing owing to tissue absorption and scattering. In this work, a PersL lifetime-based nanoplatform via deep learning was proposed for high-fidelity bioimaging and biosensing in vivo. The persistent luminescence imaging network (PLI-Net), which consisted of a 3D-deep convolutional neural network (3D-CNN) and the PersL imaging system, was logically constructed to accurately extract the lifetime feature from the profile of PersL intensity-based decay images. Significantly, the NIR PersL nanomaterials represented by Zn1+xGa2-2xSnxO4: 0.4 % Cr (ZGSO) were precisely adjusted over their lifetime, enabling the PersL lifetime-based imaging with high-contrast signals. Inspired by the adjustable and reliable PersL lifetime imaging of ZGSO NPs, a proof-of-concept PersL nanoplatform was further developed and showed exceptional analytical performance for hypochlorite detection via a luminescence resonance energy transfer process. Remarkably, on the merits of the dependable and anti-interference PersL lifetimes, this PersL lifetime-based nanoprobe provided highly sensitive and accurate imaging of both endogenous and exogenous hypochlorite. This breakthrough opened up a new way for the development of high-fidelity biosensing in complex matrix systems.

Near-Infrared Persistent Luminescence Nanoprobe for Early Detection of Atherosclerotic Plaque.

Atherosclerosis (AS) is a crucial contributor to various cardiovascular diseases (CVDs), which seriously threaten human life and health. Early and accurate recognition of AS plaques is essential for the prevention and treatment of CVD. Herein, we introduce an AS-targeting nanoprobe based on near-infrared (NIR) persistent luminescence nanoparticles (PLNPs), developing a highly sensitive NIR persistent luminescence (PersL) AS plaque imaging technique and successfully realizing early AS plaque detection. The nanoprobe exhibits good monodispersity and regular spherical morphology and also owns exceptional NIR PersL performance upon repetitive irradiation by biological window light. The surface-conjugated antibody (anti-osteopontin) endowed nanoprobe excellent targeting ability to foam cells within plaques. After intravenously injected nanoprobe into AS model mice, the highly sensitive PersL imaging technique can accurately detect AS plaques prior to ultrasonography (US) and magnetic resonance imaging (MRI). Specifically, the NIR PersL imaging reveals AS plaques at the earliest within 2 weeks, with higher signal-to-background ratio (SBR) up to 5.72. Based on this technique, the nanoprobe has great potential for applications in the prevention and treatment of CVD, the study of AS pathogenesis, and the screening of anti-AS drugs.

Size-independent boosting of near-infrared persistent luminescence in nano-phosphors via a magnesium doping strategy

Near-infrared (NIR)-emitting persistent luminescence nanoparticles (PLNPs) are ideal optical imaging contrast reagents characterized by autofluorescence-free optical imaging for their frontier applications in long-term bioimaging. Preparation of uniform small-sized PLNPs with excellent luminescence performance is crucial for biomedical applications, but challenging. Here, we report a facile magnesium doping strategy to achieve size-independent boost of NIR persistent luminescence in typical and most concerned ZnGa2O4:Cr3+ PLNPs. This strategy relies on the doping of Mg2+ ions that with similar size of Zn2+ ions in the host lattice matrix, and concomitant to the electron traps tailoring tuned by varying the feed ratio of Mg2+. The optimum Mg2+-doped PLNPs give a long afterglow time (signal-to-noise ratio (SNR) = 31.6 at 30 d) without changing the desirable uniform sub-10 nm size of the original nanocrystals. The appropriate increase of the depth and concentration of electron trap contribute jointly to the enhancement of lifetime (488 % longer, 20.57 s) and afterglow time for 700 nm persistent luminescence. Meanwhile, these PLNPs keep the original excellent rechargeability and promote over 60 times increase of SNR in renewable in vivo imaging. This simple strategy provides a basis for new opportunities to address the critical challenge of effective optical performance boost in small-sized PLNPs.

Oxygen-Tolerant Near-Infrared Organic Long-Persistent Luminescent Copolymers.

Organic materials exhibiting long-lasting emission in the near infrared are expected to have applications in bio-imaging and other areas. Although room temperature phosphorescence and thermally activated delayed fluorescence display long-lived emission of approximately one minute, organic long-persistent luminescence (OLPL) systems with a similar emission mechanism to inorganic persistent emitters can emit for several hours at room temperature. In particular OLPL with a hole-diffusion mechanism can function even in the presence of oxygen. However, ionic materials lack long-term stability in neutral organic host owing to aggregation and phase separation. In this study, we synthesized polymers with stable near-infrared persistent luminescence at room temperature via the copolymerization of electron donors and acceptors. The copolymers exhibit long-persistent luminescence (LPL) at temperatures below the glass transition temperature and can be excited by approximately the entire range of visible light. LPL properties and spectra can be controlled by the dopant.

A multi-functional nano-platform based on LiGa4.99O8:Cr0.01/IrO2 with near infrared-persistent luminescence, "afterglow" photodynamic and photo-thermal functions.

Multi-functionalised nano-platforms based on persistent-luminescence nanoparticles (PLNPs) have attracted considerable attention for biomedical applications owing to their lack of background noise and suitability for in vivo imaging without the need for in situ excitation. However, nano-platforms based on PLNPs for continuous photodynamic therapy (PDT) are currently lacking. Herein, we report a nano-platform (LiGa4.99O8:Cr0.01/IrO2, LGO:Cr/IrO2) prepared using PLNPs (LiGa4.99O8:Cr0.01, LGO:Cr) covalently bonded with iridium oxide nanoparticles (IrO2 NPs), producing near-infrared (NIR) persistent luminescence, "afterglow" PDT and photo-thermal therapy (PTT) effects. The LGO:Cr/IrO2 not only exhibits NIR-persistent luminescence at 719 nm and a PTT effect under 808 nm irradiation but also a continuous "afterglow" PDT effect without the need for in situ excitation owing to persistent energy transfer from LGO:Cr to the IrO2 NPs, in turn generating reactive oxygen species (ROS). This multi-functional nano-platform is expected to further promote the application of PLNPs in tumour treatment.

Multifunctional near-infrared long persistent luminescence phosphor BaLu2Al2Ga2SiO12:Cr3+, Tb3+ with good thermal stability, promising quantum efficiency, and excellent environmental resistance

Near-infrared (NIR) persistent luminescence (PersL) phosphors have gained significant study attention in bioimaging and biomedical fields due to the advantages of persistent emission and elimination of biological tissue autofluorescence. However, PersL phosphors generally have difficulty in guaranteeing both good thermal stability and external quantum efficiency (EQE), which limits the multi-functional applications of NIR PersL phosphors. Herein, we developed a novel multifunctional NIR PersL phosphor BaLu2Al2Ga2SiO12:Cr3+ (BLAGSO:Cr3+). Interestingly, this NIR phosphor has good thermal stability (99.7 %@150 °C for BLAGSO:0.03Cr3+) and promising EQE (31.08 % for BLAGSO:0.03Cr3+). To further improve its PersL performance, Tb3+ ion which is believed to act as a modulator of matrix defects and enhances the storage capacity of traps for electrons is introduced into BLAGSO:0.03Cr3+ and an optimal PersL duration of more than 48 h is achieved. Meanwhile, BLAGSO:0.03Cr3+, 0.03 Tb3+ also exhibits good photo-stimulated PersL (PSPL) ability, and the quenched PersL can be rejuvenated by external photo-stimulation. The potential uses of BLAGSO:0.03Cr3+, 0.03 Tb3+ in NIR pc-LEDs and bioimaging are explored and demonstrated. This work is anticipated to drive the research of multifunctional NIR PersL phosphors.

Facilitating Near-Infrared Persistent Luminescence in Cr3+ -Doped Gadolinium Gallium Garnets.

Near-infrared persistent luminescence (NIR PersL) materials provide great potential in the fields of night vision, biological imaging, and information encryption. However, among various crystal structures, Cr3+ -dopedgalliumgarnets show inferior PersL property, which turns out to be the bottleneck of their versatile applications. The rational design and facile preparation of high-performance NIR PersL materials are crucial for the emerging applications. In this work, a series of Gd3 Mgx Gex Ga5-2x O12 :Cr3+ (x = 0, 0.25, 0.5, 0.75, 1) is investigated by microwave-assisted solid-state (MASS) approach. Furthermore, by employing chemical composition co-substitution, PersL performance is further improved and the optimum working temperature is adjusted to the lower temperature at 10°C. Trap level distribution of Gd3 Mg0.5 Ge0.5 Ga4 O12 :Cr3+ phosphor is revealed based on the temperature and fading-time dependent PersL and thermoluminescence property. Further study demonstrates the reduction of the bandgap and the trap distribution forwards at shallow-lying trap energy levels. The synergistic effect, from both energy-band manipulation and trap-level optimization, facilitates NIR PersL in Cr3+ -doped gadolinium gallium garnets. These findings confirm the applicability of MASS-based bandgap and defect level engineering for improving the PersL properties in non/inferior-PersL materials. This burgeoning MASS method may facilitate a wide range of PersL materials for various emerging applications.

Trap engineering in LiInSi2O6:Cr,Pr by excess cristobalite silica for X-ray activated near-infrared persistent luminescence imaging in vivo

Chromium-doped persistent luminescence nanoparticles (PLNPs) have promising biomedical applications in X-ray charged near-infrared (NIR) luminous imaging. The persistent luminescence (PersL) property was usually adjusted by co-doping with other ions. Impurity phases were thought to be adverse to the PersL. In this study, a composite material, LiInSi2O6:Cr,Pr·2SiO2 (LICP-S), was synthesized with a PersL peak at 800 nm after being charged by 1 Gy X-ray while LiInSi2O6:Cr (LIC) and LiInSi2O6:Cr,Pr (LICP) possessed no or very weak PersL. Distinctively, excess metastable cristobalite silica was found essential for the much more intense PersL of LICP-S than LICP and LIC. Thermostimulated luminescence spectra studies indicated that cristobalite adjusted the Pr-related traps from deep traps to shallow ones, which facilitated the room temperature PersL. The low dose X-ray charged PersL of LICP-S was applied to demonstrate the luminous labeling of a medical silicone prosthesis that was supposed to be imbedded in body for years via X-ray activated PersL imaging in vitro and in vivo. This work not only provides a kind of PLNPs with 800 nm emission suitable for low dose X-ray activation, but also an unusual strategy for trap engineering in PersL materials by designing multi-phase composites.

Incorporation of Eu3+ in ZnGa2O4:Ni2+ for improved NIR persistent luminescence located in second transparency window

AbstractIt is well known that near‐infrared (NIR) persistent phosphors have rather low absorption coefficients of biological tissues for NIR light. However, recent research shows that the phosphors emitting NIR lights in second NIR (NIR‐II, 1000–1350 nm) and third (NIR‐III, 1500–1800 nm) biological window have advantages over that in NIR‐I (650–900 nm). Although ZnGa2O4:Ni2+ outputs NIR emission and afterglow locatedin NIR‐II, the weak signal significant limits its application. In this work, persistent luminescent phosphors of ZnGa2O4:xNi2+, yEu3+ (x = 0–0.013, y = 0.01–0.06) (termed as ZEGN) were synthesized via a traditional high‐temperature solid‐state reaction, which feature a broad emission band in the NIR‐II window. The phosphors exhibit a broad NIR emission at about 1300 nm after ultraviolet (UV) or orange–red lights excitation, arising from the 3T2(3F) → 3A2(3F) transition of Ni2+. However, incorporation of Eu3+ ions, the NIR emission intensity significantly increases with the increase of Ni2+ ion concentration, reaching the maximum by 18 times at x = 0.005. Removing the light source, the sample still outputs intense NIR afterglow and red afterglow that can last over 500 s. It is noteworthy that the red afterglow of Eu3+ shows a dramatically decrease but the NIR afterglow increases with increasing the Ni2+ ion concentration, because of energy transfer. Under the excitation of 282‐nm UV light, the ZGEN sample exhibits a good thermal stability. The phosphor offers a promising application in biological imaging due to broadband NIR‐II light and afterglow.

Effect of the Elaboration Method on Structural and Optical Properties of Zn1.33Ga1.335Sn0.33O4:0.5%Cr3+ Persistent Luminescent Nanomaterials.

Near-infrared (NIR) persistent luminescence (PersL) materials have demonstrated promising developments for applications in many advanced fields due to their unique optical properties. Both high-temperature solid-state (SS) or hydrothermal (HT) methods can successfully be used to prepare PersL materials. In this work, Zn1.33Ga1.34Sn0.33O4:0.5%Cr3+ (ZGSO:0.5%Cr3+), a newly proposed nanomaterial for bioimaging, was prepared using SS and HT methods. The results show the crystal structure, morphology and optical properties of the samples that were prepared using both methods. Briefly, the crystallite size of the ZGSO:0.5%Cr3+ prepared using the SS method is ~3 µm, and as expected, is larger than materials prepared using the HT method. However, the growth process used in the hydrothermal environment promotes the formation of ZGSO:0.5%Cr3+ with more uniform shapes and smaller sizes (less than 500 nm). Different diameter ranges of nanoparticles were obtained using HT and ball milling (BM) methods (ranging from 25-50 nm) and by using SS and BM methods (25-200 nm) as well. In addition, the SS-prepared microstructure material has stronger PersL than HT-prepared particles before they go through ball milling to create nanomaterials. On the contrary, after BM treatment, ZGSO:0.5%Cr3+ HT and BM NPs present higher PersL and photoluminescence (PL) properties than ZGSO:0.5%Cr3+ SS and BM NPs, even though both kinds of NPs present worse PersL and PL compared to the original particles before BM. To summarize: preparation methods, whether by SS or HT, with additional grinding as a second step, can have a significant impact on the morphological and luminescent features of ZGSO:0.5%Cr3+ PersL materials.

Bright, small sizes and hydro-dispersive NIR persistent luminescence nanoparticles modified with Si and amino groups for enhanced bioimaging

Near-infrared (NIR) persistent luminescence nanoparticles (PLNPs) with high brightness, small sizes, good hydro-dispersivity, and intrinsic surface-functional groups are desirable in biological applications. In this work, Cr3+-doped zinc gallogermanates Zn1+x Ga2−2x Ge x O4:Cr (ZGGC) PLNPs were hydrothermally synthesized via 3-aminopropyltriethoxysilane (APTES) as an additive, or APTES and cetyltrimethylammonium bromide (CTAB) as two co-additives. Addition of APTES not only dramatically enhances the 696 nm NIR luminescence intensity, but also obviously decreases the particle size and introduces amino groups. In particular, the x = 0.1 series ZGGC (ZGGC0.1) with the addition of n moles equivalent APTES (ZGGC0.1-nA) had smaller particle sizes than the x = 0.2 counterpart (ZGGC0.2-nA). The NIR afterglow intensities increased with the APTES introduction. The ZGGC0.2-2.5A sample (also named as ZGGC, Si, -NH2) exhibited maximum luminescence intensities both in solid and aqueous states. With APTES, Si atom is doped and –NH2 groups are modified, the trap depth and density become larger, and the afterglow intensities and decay time are significantly enhanced. More notably, co-addition of CTAB (ZGGC0.2-2.5A-C) (also named as ZGGC, Si, −NH2’) further enhances hydro-dispersivity and luminescence intensity, decreases particle sizes, and results in more prominent amino groups. The trap density is drastically higher than that without CTAB (i.e. ZGGC0.2-2.5A). Change of Cr3+ microenvironment in the crystal and more defects introduction contribute to the enhanced brightness. As expected, the ZGGC,Si,-NH2’ PLNPs possess excellent biocompatibility, deep tissue penetration and distinguished bioimaging properties, and rechargeability with orange LED light. The ZGGC,Si,-NH2’ PLNPs should provide to be an excellent nanomaterial for various functionalization and bioimaging applications.

Broadband and Multimode Near‐Infrared Emitter Based on Cr3+‐Activated Stannate for Multifunctional Applications

AbstractBroadband near‐infrared (NIR) phosphors have recently received considerable attention in spectroscopy technology fields, but designing inexpensive, emission peaks centered above 800 nm, and multimodal broadband NIR luminescence material still remains a great challenge. Here, by selecting stannate compound Mg2SnO4 (MSO) as the host, a kind of broadband NIR phosphor MSO:Cr3+ with multimode luminescence properties is reported. The designed material exhibits an emission peaking at 800 nm and a full‐width at half maximum of 180 nm (≈2730 cm−1). The site occupation of Cr3+ in MSO is unraveled by density functional theory calculation. The constructed NIR light‐emitting device based on MSO:Cr3+ displays a high NIR output power of 187.19 mW@100 mA and remarkable photoelectric efficiency of 13.67%, and its multifunctional applications in information encryption, non‐destructive detection, and so on are also demonstrated. Additionally, through defect site reconstruction, MSO:Cr3+ presents superior broadband NIR persistent luminescence (PersL) properties with PersL duration time longer than 50 h. This work provides a feasible strategy to develop intelligent optical material integrated with multimodal luminescence through low‐cost stannate compounds as the host toward versatile applications such as non‐destructive detection and bioimaging.

Persistent luminescent metal-organic framework nanocomposite enables autofluorescence-free dual modal imaging-guided drug delivery.

Molecular imaging-guided therapy was essential for realizing precise cancer intervention, while designing an imaging platform to achieve autofluorescence-free imaging for dual modal imaging-guided drug delivery remains a challenge. Near-infrared persistent luminescence nanoparticles (NIR PLNPs) were promising for tumor imaging due to no background interference from the tissue. Herein, a persistent luminescent metal-organic framework (PLNPs@MIL-100(Fe)) is prepared via a layer-by-layer method for dual-modal imaging-guided drug delivery. The PLNPs@MIL-100(Fe) exhibit NIR persistent luminescence emitting and T2-weighted signal, achieving precise in vivo dual-modal imaging of tumor-bearing mice by providing high spatial resolution MR imaging and autofluorescence-free NIR imaging. The porous MIL-100(Fe) shell provides PLNPs@MIL-100(Fe) with up to 87.1% drug loading capacity and acid-triggered drug release for drug delivery. We envision that the proposed PLNPs@MIL-100(Fe) platform would provide an effective approach for precise tumor imaging and versatile drug delivery.

Dual-Triggered Near-Infrared Persistent Luminescence Nanoprobe for Autofluorescence-Free Imaging-Guided Precise Therapy of Rheumatoid Arthritis.

Rheumatoid arthritis (RA) is a common, chronic, and highly disabling autoimmune disease characterized by difficult treatment, long disease duration, and easy recurrence. The development and application of high-sensitivity theranostic probes for RA that will facilitate precise monitoring of disease progression and enable effective treatment are currently hotspots in the field of RA theranostics. In this study, mZMI@HA, a dual-triggered theranostics nanoprobe, is constructed based on near-infrared persistent luminescence nanoparticles (NIR-PLNPs) for precise RA treatment and therapeutic evaluation. This is the first reported use of high-sensitivity autofluorescence-free imaging based on NIR-PLNPs for precise RA treatment and therapeutic evaluation. Compared with the NIR fluorescence imaging probe-indocyanine green, the signal-to-background ratio of persistent luminescence (PersL) imaging is improved nearly 14-fold. Using PersL imaging to guide photothermal therapy and controllable drug release through NIR/pH-responsiveness, the progress of collagen-induced RA is relieved. Additionally, the therapeutic evaluation of RA by PersL imaging is consistent with clinical micro-computed tomography and histological analyses. This study demonstrates the potential of NIR-PLNPs for high-sensitivity imaging-guided RA treatment, providing a new strategy for RA precise theranostics.

LiGa5O8:Cr3+@PEG nanomaterials with near-infrared-persistent luminescence for bioimaging applications

Bioimaging is considered a convincing imaging method. The near-infrared Persistent Luminescence Nanoparticles(NIR PLNPS) have demonstrated great perspectives for application in the bioimaging field due to their unique optical properties. The high-temperature solid-phase(HT) methods cannot be used for bioimaging applications due to the existence of large particle size. On the other hand, the sol-gel (S-G) and the hydrothermal(Hy) methods can successfully prepare the LGO: Cr nanomaterials. In this work, a LiGa5O8:Cr3+(LGO: Cr) NIR PLNPS was prepared by S-G and Hy methods, and the employed nanomaterials were treated by PEG(Polyethylene glycol) modification to reduce the toxicity. The acquired results clearly show that the average particle size of the samples that were prepared by enforcing the S-G method is larger than that of the Hy method. However, their luminescence performance is better than that of the samples prepared by Hy method, and there are differences in trap characteristics. Synthetically, LGO: Cr@PEG(Hy) is suited for biological imaging due to its lower toxicity, and cell imaging by LGO: Cr@PEG(Hy)was successfully achieved.

Novel broadband near-infrared emitting long afterglow phosphor MgGeO3: Cr3+

In this study, we report broadband near-infrared persistent luminescence of a novel MgGeO3: Cr3+ material. The luminescence can be excited by the ultraviolet radiation and detected for more than 16 h. Optical and electron paramagnetic resonance spectroscopy experiments suggest that the observed bands appear as a result of interaction between Cr3+ luminescence centre and oxygen-impurity complexes and oxygen vacancy related trapping states. Thermally stimulated luminescence analysis revealed that the states are closely overlapping and lie relatively deep in the band gap with the activation energy exceeding 0.9 eV. The experimental data strongly suggest that the main detrapping route for the trapped charge carriers in the MgGeO3: Cr3+ material is athermal tunnelling directly to the luminescence centres.

A Chlorotoxin‐Directed Diselenide‐Bridged Tumor‐Homing Persistent Luminescence Nanoprobes Mediating Inhibition of Oxidative Phosphorylation for Long‐Term Near‐Infrared Imaging and Therapy of Glioblastoma

AbstractGlioblastoma (GBM) is the most prevailing malignant primary brain tumor, and the precise diagnosis of GBM has always been a challenge. Gboxin is a recently developed drug efficiently inhibiting the oxidative phosphorylation in GBM cells, and both the chlorotoxin (CLTX) and GBM cell membrane coating are capable of GBM targeting and tumor homing. Herein, the near‐infrared (NIR) persistent luminescence (PL) nanoparticle, CUDZG, with a dual function of imaging and therapy is developed based on ZnGa2O4:Cr3+,Sn4+. CUDZG exhibits superior rechargeable NIR PL for at least 48 h with excellent tissue penetration in vivo, which enables the longstanding autofluorescence‐free imaging of the orthotopic GBM. The tumor growth of both the orthotropic and subcutaneous GBM‐bearing mice are significantly suppressed by CUDZG. This is the first‐time report of 1) the integration of CLTX and cell membrane coating for drug delivery, 2) diselenide‐based trigger release for anti‐GBM therapy, and 3) the systemic delivery of Gboxin. This study also offers an example of the highly promising blood‐brain penetrable drug carriers for precise diagnosis and therapy of central nervous system diseases.

Incorporation of Mg2+/Si4+ in ZnGa2O4:Cr3+ to Generate Remarkably Improved Near-Infrared Persistent Luminescence

Near-infrared emitting nano-sized particles of ZnGa2−x(Mg/Si)xO4:Cr3+ (x = 0–0.15, termed as ZGMSO:Cr3+) with persistent luminescence were prepared by sol-gel processing followed by calcination. The samples were tested by XRD, TEM, STEM, SAED, Raman, XPS, UV-Vis-NIR, TL, PLE/PL spectroscopy, and persistent luminescence decay analysis. Equimolar incorporation of Mg2+ and Si4+ ions did not change the spindle structure of ZnGa2O4 seriously. Most Mg2+ ions are more likely to occupy the sites in octahedron, but Si4+ ions are more likely to occupy the sites in tetrahedron in priority. A broader bandgap, up shift of conduction band minimum, and more anti-defects were found at a higher Mg2+/Si4+ doping concentration. ZGMSO:Cr3+ outputs near-infrared emission with a dominated band at 694 nm (2E → 4A2 transition of Cr3+), which can last longer than 48 h after the stoppage of UV irradiation. Mg2+/Si4+ doping contributes to a better near-infrared persistent luminescence, and the strongest and the longest NIR afterglow was observed at x = 0.05, owing to that the x = 0.05 sample has the deepest defects. The synthesized nanoparticles of ZGMSO:Cr3+ not only output intense NIR afterglow but also can be recharged by the red light of LED several times, indicating that they are the potential nano probes for bio imaging in living animals.

One-step construction of bifunctional nanoprobes for NIR afterglow and T2-weighted MR imaging

In this study, spinel-phase Zn2Ga3-xFe3+xGe0.75O8 (x = 0, 0.002, 0.004, 0.02, 0.04, 0.08, 0.2) and Zn2Ga2.98-xFe3+xCr0.02Ge0.75O8 (x = 0, 0.0004, 0.001, 0.002 0.003, 0.004) nanoparticles were prepared by one-step hydrothermal method in combination with vacuum annealing. For ZGGO: Fe3+ nanoparticles, the near infrared (NIR) emissions (∼725 nm) originate from the 4T1(4G)→6A1(6S) transition of Fe3+ occupying octahedral and tetrahedral sites of Ga3+. Furthermore, their afterglow time is more than 15 min and Fe3+ doping will influence the generation of antisite defects pair (GaZn0−ZnGa′). For Cr3+ and Fe3+ co-doped ZGGO nanoparticles with average size of ∼46 nm, the NIR persistent luminescence around ∼700 nm, originating from the 2E→4A2 and 4T2→4A2 transitions of Cr3+, can be observed and the afterglow time exceeds 850 min. With the increase of Fe3+ concentration, the afterglow intensity decreases due to the decreased number of (GaZn0−ZnGa′) defects and deeper traps. In particular, autofluorescence-free imaging and MR imaging were successfully realized by using ZGGO: Cr3+, Fe3+0.002 nanoparticles dispersed in the simulated biological fluid environments (H2O, SLS and HSA). Their clear afterglow images can be acquired within 3 min after the stoppage of the UV irradiation and their transversal relaxivity (r2) is in the range of 227–140 mM−1s−1, which is close to the conventional Feridex T2 agent (108 mM−1s−1). Our results suggest that ZGGO: Cr3+, Fe3+ nanoprobes have potential applications in the diagnosis and therapy of disease.