The Ag ions were introduced into the Bi doped silicogermanate glasses by Ag + for Na + ion exchange method. After ion exchange, the X-ray photoelectron spectroscopy (XPS) spectrum implied the Ag ions were mainly in ionic form (Ag + ) within the glasses. With the increase of the Ag + concentration, more relaxation of local structure would be induced at the non-bridging oxygen (NBO), meaning that the network gave more negative sites. Bi 3+ ions could be reduced to lower valence states of Bi containing Bi near infrared (NIR) active centers with the depolymerization of glass network, resulting in the enhancement of the Bi NIR luminescence. After heat treatment, the XPS, absorption spectra and transmission electron microscope (TEM) images revealed Ag nanoparticles (Ag NPs) formed in glasses. With the increase of the Ag NPs concentration, more NBOs released from Ag + , which led to reduce more Bi 3+ ions to lower valence states of Bi containing Bi NIR active centers, resulting in further enhancement of the NIR luminescence. Our research may extend the understanding of structural modulation in Bi valence states and offer a valuable way to enhance the NIR luminescence of Bi in glasses.
Near-infrared (NIR) long persistent luminescent materials, with broad potential applications, have attracted significant research interest, though most studies focus on room-temperature performance. However, designing and synthesizing long-persistent luminescent materials that can form a large number of stable shallow traps at lower temperatures is extremely challenging. In this paper, a series of Cr-doped broadband near-infrared silicon germanate long persistent luminescent phosphors were synthesized by the high-temperature solid-phase method. The optical properties and crystal structural parameters of the phosphors at room temperature were studied systematically. The specific luminescence sources and reasons for the broadening of emission peaks have been discussed. The significant differences in persistent luminescence at different temperatures are caused by the substitution of Ge-Si chemical units in the Na₂CaGe x Si 6-x O₁₄ matrix doped with Cr³⁺ ions. Among the samples, Na 2 CaGe 4 Si 2 O 14 :0.4 mol% Cr 3+ shows excellent persistent luminescence properties and abundant shallow traps at low temperature. This phosphor was tested at low temperature to investigate its potential as an indicator for the temperature changes of biologics.
Silicogermanate (JU110) with an interrupted open-framework has been synthesized by using a hydrothermal method using 1,1′-(1,4-phenylenebis(methylene))bis(1-methylpyrrolidin-1-ium) hydroxide as an organic structure-directing agent (OSDA). Silicon and fluoride anions were introduced to the concentrated-gel synthesis system, and different synthetic parameters influencing the synthesis were discussed. The structure of JU110 was characterised by using rotation electron diffraction (RED) and high-resolution powder X-ray diffraction. JU110 crystallizes in the space group Fm2m (No. 42) with a = 13.9117(2) Å, b = 18.2980(3) Å and c = 32.7800(6) Å. The structure is constructed by the sti layers found in the STI framework that are pillared by D4R/Ge7 units to form a large cavity, showing 10-ring openings along [100] and 9-ring openings along [110]. Thermal stability studies showed that the framework was maintained with the loss of water molecules, but collapsed with the removal of charge-compensating cations.
Near-infrared persistent luminescence materials have recently attracted considerable attention in the field of bio-imaging, food analysis, anti-counterfeiting, etc. However, the limited number of efficient emitters restricts their further development. Herein, a novel broadband near-infrared long persistent phosphor Na 2 CaGe 5 SiO 14 :xCr 3+ was synthesized using a high-temperature solid-phase method. Its emission range is mainly within 600–900 nm, and the persistent luminescence duration of the phosphor with the optimal doping concentration is more than 12 h. The optical properties of the samples and the relationship between the crystal field and chromium ion concentration were systematically investigated by UV diffuse reflectance spectra as well as fluorescence spectra, and the occupancy of Cr 3+ ions in the Na 2 CaGe 5 SiO 14 matrix was probed. The energy transfer process between Cr 3+ ions at different temperatures and the decay behavior at different emission wavelengths were further analyzed in conjunction with low-temperature spectra and photoluminescence decay curves. Finally, Cr ion-doped silicogermanate near-infrared long persistent luminescent materials were tested for biological tissue penetration, demonstrating their potential applications in bio-imaging.
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