Phonon sideband induced broadband far-red emission Li2GeTeO6:Mn4+ phosphors under blue-excitation for plant-cultivation LEDs, w-LEDs, and security ink

•Li2GeTeO6:Mn4+ phosphors are firstly synthesized via solid-state reaction and have high phase purity.•The phosphor emits bright asymmetric broadband far-red light excited by 300 nm.•Li2GeTeO6: 0.4 mol%Mn4+ possesses high IQE.•Li2GeTeO6:Mn4+ phosphors have potential to be used for plant-cultivation LEDs w-LEDs, and security ink. The development of far-red-emitting phosphors for plant-cultivation LEDs encounters challenges such as achieving stable, efficient emission and mitigating issues related to toxicity and moisture sensitivity in fluoride-based phosphors. Additionally, optimizing phosphors for security ink and high-performance white LEDs (w-LEDs) remains a critical gap. This study addresses these issues by synthesizing Li2GeTeO6:Mn4+ (LGTO: Mn4+) phosphors via a high-temperature solid-phase method. Therein, LGTO fell within the category of indirect band gap material and the band gap is 2.99 eV that allowed for the incorporation of Mn4+ions. The broadband far-red emission (4T2g→4A2g​) of Mn4+ ions is attributed to strong electron-phonon coupling, where the PL spectrum is broadened due to significant contributions from phonon sidebands (PSBs). At x= 0.4 mol%, the LGTO: xMn4+ phosphors have the optimal doping concentration. LGTO: 0.4 mol%Mn4+ phosphor exhibits exceptional internal quantum efficiency and color purity. The decay lifetime of LGTO: 0.4 mol%Mn4+ phosphor is 0.332 ms. The fabricated plant-cultivation LED (λchip= 450 nm) achieves a high overlap with the Pfr absorption spectrum. Furthermore, the w-LEDs demonstrate a high color rendering index, a suitable correlated color temperature, and a moderate luminous efficacy. The bright pink emission under UV light also highlights its potential in security ink applications. These findings position LGTO: Mn4+ phosphors as promising candidates for advancing plant growth lighting, high-performance w-LEDs, and anti-counterfeiting technologies. [Display omitted]