Hybrid coordination-network-engineering for bridging cascaded channels to activate long persistent phosphorescence in the second biological window

The optical research progress of nanophosphors composed of transition elements in the fourth period of near-infrared windows I and II for deep-tissue theranostics

Research in the field of nano-optics is advancing by leaps and bounds, among which near-infrared (NIR) light optics have attracted much attention. NIR light has a longer wavelength than visible light, such that it can avoid shielding caused by biological tissues. This advantage has driven its importance and practicality in human treatment applications and has attracted significant attention from researchers in academia and industry. In the broad spectrum of infrared light wavelengths, the most noticeable ones are the NIR biological window I of 700-900 nm and window II of 1000-1700 nm. Luminescent materials can effectively cover the NIR biological window with different doping strategies. These doped elements are mostly transition elements with multielectron orbitals. Several nanomaterials based on narrow-spectrum lanthanides have been developed to correspond to biological applications of different wavelengths. However, this review explicitly introduces the absorption and reflection/luminescence interactions between NIR light and biological tissues independently. Unlike the adjustment of the wavelength of the lanthanide series, this review analyzes the NIR optical properties of the fourth-period element ions in transition elements (such as Cr³⁺ and Ni²⁺). These elements have a broadband wavelength of NIR light emission and higher quantum efficiency, corresponding to the absorption and emission spectrum and photobiological absorption of different NIR windows for therapeutic diagnosis. Finally, this review lists and explores other broadband NIR phosphors and has tried to discover the possibility of non-invasive precision medicine in the future.

Multiple emission bands NIR-persistent luminescence mSiO2@Zn0.6Ca0.4Ga2O4:Cr3+,Yb3+ nanoparticles for biological applications

Persistent luminescence nanoparticles (PLNPs) emitting in the NIR window (700-1700 nm) have shown great promise in the field of fluorescence imaging due to their unique properties, including the absence of in situ excitation and low optical scattering in tissues. However, they are still facing some challenges, such as irregular shape, wide size distribution and poor persistent luminescence performance. Here, we report a facile mesoporous template method for synthesizing mSiO₂@Zn_0.6Ca_0.4Ga₂O₄:Cr³⁺,Yb³⁺ (mSiO₂@ZCGO) persistent luminescent nanoparticles, which show a regular morphology and a size of about 69 nm. In addition, these nanocrystals exhibit persistent luminescence in multi-NIR windows, the first infrared window (∼696 nm of Cr³⁺ emission) and second infrared window (∼1000 nm of Yb³⁺ emission). Under illumination of a 254 nm UV lamp for 10 min, the persistent time of Cr³⁺ ions and Yb³⁺ ions lasted more than 120 min and 10 min, respectively. In particular, the NIR persistent emission of mSiO₂@ZCGO could be stimulated by soft X-ray, which is beneficial to long-term imaging in deep tissues. The optical penetration length of Yb³⁺ ions persistent luminescence was evaluated to be 2.8 mm. These results demonstrate the great promise of mSiO₂@ZCGO for deep-tissue bio-imaging.

Afterglow, TL and OSL properties of Mn2+-doped ZnGa2O4 phosphor

Zinc gallate (ZnGa₂O₄) spinel ceramics doped with Mn²⁺ ions was prepared by a solid-state reaction at 1200 °C in air. Manganese concentration was equal to 0.05 mol.% of MnO with respect to ZnO. Ceramics produced in this way show an efficient green emission at about 505 nm under UV or X-ray excitations, which is caused by Mn²⁺ ions. This green emission is observed also as a relatively long afterglow (visible to the naked eye in the dark for about one hour) after switching-off the X-ray excitation. Time profiles of the beginning of glow and afterglow have been studied together with thermally stimulated (TSL) and optically stimulated (OSL) luminescence. Experimental results demonstrate a presence of few types of shallow and deep traps responsible for the observed afterglow and TSL/OSL emission of the material. The possibility of pulsed optical stimulation and time-resolved OSL characteristics of ZnGa₂O₄: Mn²⁺ has been reported for the first time. The presented results suggest the ZnGa₂O₄: Mn²⁺ spinel as a promising material for further fundamental research and possibility of application as a green long-lasting phosphor or storage phosphor for TSL/OSL radiation dosimetry.

Recent progress in biomedical applications of persistent luminescence nanoparticles

Persistent luminescence nanoparticles (PLNPs) are an emerging group of promising luminescent materials that can remain luminescent after the excitation ceases. In the past decade, PLNPs with intriguing optical properties have been developed and their applications in biomedicine have been widely studied. Due to the ultra-long decay time of persistent luminescence, autofluorescence interference in biosensing and bioimaging can be efficiently eliminated. Moreover, PLNPs can remain luminescent for hours, making them valuable in bio-tracing. Also, persistent luminescence imaging can guide cancer therapy with a high signal-to-noise ratio (SNR) and superior sensitivity. Briefly, PLNPs are demonstrated to be a newly-emerging class of functional materials with unprecedented advantages in biomedicine. In this review, we summarized recent advances in the preparation of PLNPs and the applications of PLNPs in biosensing, bioimaging and cancer therapy.