Tailoring of the trap distribution and crystal field in Cr3+-doped non-gallate phosphors with near-infrared long-persistence phosphorescence

We present a series of efficient near-infrared (NIR) Cr3+-doped non-gallate long-persistence phosphors (Zn2SnO4: Cr and Zn(2-x)Al2xSn(1-x)O4: Cr) and highlight their special optical characteristics of broad emission band (650–1200 nm, peaking at 800 nm) and long afterglow duration (>35 h). In the context of materials selection, these systems successfully avoid the existing ubiquitous reliance on gallates as hosts in Cr3+-doped phosphorescent phosphors. Zn2SnO4 is employed as a host to take advantage of its characteristic inverse spinel crystal structure, easy substitution into Zn2+ and Sn4+ sites by Cr3+ in distorted octahedral coordination and non-equivalent substitution. In this work, Al dopant was introduced both to precisely tailor the local crystal field around the activator center, Cr3+, and to redeploy trap distribution in the system. Indeed, such redeployment permits band gap adjustment and the dynamic variation of the annihilation and the formation of defects. The results demonstrate that the method employed here can be an effective way to fabricate multi-wavelength, low-cost, NIR phosphorescent phosphors with many potential multifunctional bio-imaging applications. An international team has found a way to lower the cost and tune the emission properties of phosphorescent probes used for bioimaging. Long phosphorescent phosphors are newly developed materials that can absorb energy and release it as biologically compatible, near-infrared light over extended time frames. Typically, long phosphorescent phosphors rely on gallium ions for super-long emission, but gallium is becoming increasingly expensive. Jianrong Qiu from Guangzhou, China, and co-workers sought a cheaper alternative based on a zinc-tin oxide doped with chromium and/or aluminum atoms. The compound structure allowed the crystal field surrounding the transition metals to be easily modified through using dopants and defects; in turn, this crystal field change significantly affected the phosphorescence. Careful fabrication strategies uncovered new gallium-free phosphors that operate at multiple wavelengths and radiate for longer than 35 hours. Novel Cr3+-doped non-gallate near-infrared phosphorescent phosphor, Zn2SnO4: Cr, with the special optical characteristics of broad emission band (650–1200 nm, peaking at 800 nm) and long afterglow duration (>35 h) was presented, which successfully avoid the existing ubiquitous reliance on gallates as hosts in Cr3+-doped phosphorescent phosphors. This research also deals with the method of finely tailoring the local crystal field around the activator center, Cr3+, along with essential redeployment of trap distributions by adding Al. Indeed, such redeployment permits band gap adjustment and the dynamic variation of the annihilation and formation of defects.