Multi-color persistent luminescence (PersL) inorganic phosphors hold great potential in applications such as sensing, information storage and display, and anticounterfeiting fields. In this work, we synthesized dual-color-emitting PersL submicron particles using a sonochemical approach. A quaternary oxide, (Mg,Zn)xGeOy (MZGO) was synthesized as the host lattice, with multi-color emission achieved by a single dopant Mn2+. Additionally, we demonstrated the potential of MZGO particles for dynamic, multimodal anticounterfeiting applications by utilizing their excitation-dependent emission colors and PersL durations.

Near-infrared persistent luminescence (PersL) nanoparticles (NPs) have great potential in biomedical applications due to their ability to continuously emit tissue-penetrating light. Despite numerous reports on the distribution, biological safety and other consequences of PersL NPs in vitro and in vivo, there has been a lack of studies on the optical properties of these NPs in the physiological environment. In light of this, we investigated the effects of short-term immersion of the prominent Cr3+-doped ZnGa2O4 (CZGO) NPs in a simulated physiological environment for up to 48 h. This paper reports the changes in the structural and optical properties of CZGO NPs after their immersion in a phosphate-buffered saline (PBS) solution for pre-determined time intervals. Interestingly, the luminescence intensity and lifetime noticeably improved upon exposure to the PBS media, which is unusual among existing nanomaterials explored as bioimaging probes. After 48 h of immersion in the PBS solution, the CZGO NPs were approximately twice as bright as the non-immersed sample. X-ray spectroscopic techniques revealed the formation of ZnO, which results in an improvement in observed luminescence.

Persistent luminescence (PersL) materials are excellent candidates in the dynamic and multimodal anticounterfeiting field. Compared to commercially available micrometer-sized PersL phosphors, nanosized PersL materials could blend more easily with solvents and allow printing patterns with fine details. MgGeO3 is one of the frequently employed lattice hosts for PersL phosphors. It can accommodate divalent ions such as Mn2+ to produce deep-red PersL. In this work, MGO:Mn nanorods are synthesized, for the first time, with a uniformly distributed morphology. These nanorods exhibit more intense and longer-lasting PersL. 

Chromium(III)-doped zinc gallate (CZGO) is one of the representative persistent luminescent (PersL) phosphors emitting in the near-infrared region. The PersL mechanism dictates that such a phenomenon is only profound in large crystals, so the preparation of CZGO with sizes small enough for biological applications while maintaining its luminescence remains a challenging task. In this work, CZGO was incorporated in mesoporous silica nanoparticles (MSNs). It was observed that forming a CZGO@MSN nanocomposite could enhance the luminescence intensity and extend the PersL lifetime of CZGO. X-ray absorption fine structure (XAFS) analysis was conducted to investigate the local structure of Zn2+, and an interaction between Zn2+ in CZGO and the MSN matrix was identified.

In this work, Cr3+-doped ZnGa2O4 (CZGO) nanoparticles are incorporated into an amorphous calcium phosphate (ACP) matrix to form a nanocomposite. Utilizing adenosine triphosphate (ATP) as an organic phosphorus source, the luminescence of the CZGO@ACP composite was significantly brighter and longer-lasting compared to bare CZGO. We found that these improved optical properties were present only when an organic phosphorus source (instead of the conventional inorganic phosphate salt, (NH4)2HPO4) was used as the ACP precursor. We used synchrotron-based X-ray absorption fine structure to unravel the unique interaction between CZGO and ATP. Lastly, through collaborative aid from Dr. Arghya Paul’s group, in vitro cytocompatibility and antibacterial tests revealed an improvement in biocompatibility when using ATP as the phosphorus source to form the nanocomposite.

Shine bright: Persistent luminescent Cr-doped ZnGa2O4 (CZGO) is incorporated into an amorphous calcium phosphate (ACP) matrix. Annealing CZGO prior to ACP integration greatly improves its luminescence intensity and duration. Zn2+ redistribution from CZGO to ACP is identified, leading to the formation of Zn3(PO4)2 when immersed in water. The nanocomposite exhibits high stability under prolonged X-ray exposure.

PersL nanoparticles with dual emission bands based on MgGeO3 was investigated. Introducing Yb3+ as a second dopant enables a deep-red-to-NIR energy transfer, producing dual-emission at both deep-red and NIR. The NIR emission can be further enhanced by the addition of Li+. A detailed spectroscopy study is performed to investigate the local structure around the light activators. We found that adding the Yb3+ and Li+ changes the preferred site of occupancy for Mn2+, and when Mn2+ is shifted to a site that emits deep-red less efficiently, it acts as an electron trap to extend the PersL of the NIR-II emission.