A novel far-red-emitting phosphor Ca2InTaO6:Mn4+ with excellent responsiveness to phytochrome PFR for plant growth

A series of novel Ca2InTaO6 perovskite compounds doped with Mn4+ ions were successfully synthesized via the conventional solid-state method at elevated temperatures. The X-ray powder diffraction (XRD) technique was utilized to capture the phase structure. Based on the analysis of diffuse reflection (DR) spectra and density functional theory (DFT) calculations, it can be concluded that Ca2InTaO6 exhibits characteristics of an indirect semiconductor with a band gap Eg = 3.526 eV. With a 367 nm excitation, the Mn4+-doped Ca2InTaO6 exhibits a far-red emission at 689 nm, corresponding to the 2E1g to 4A2g transition. The photoluminescence (PL) characteristics of the sample align well with the absorption properties of phytochrome far-red light (PFR). Based on analysis using the Tanabe-Sugano diagram, it can be inferred that Mn4+ is situated in a highly intense crystalline field for the 2E1g state. At concentration x = 0.006, the most optimal Mn4+ doping was achieved, ascribing to the nearest neighbour ion interaction. The internal quantum efficiency (IQE) is 35.48 %. The Commission International del'Eclairage (CIE) coordinates of a red LED fabricated with Ca2InTaO6:0.006Mn4+ phosphor is located in the red region. Moreover, the electroluminescent spectrum (EL) exhibited by the enclosed lamp has a larger overlapping with the chlorophyll PFR (85.68 %) than PR (22.27 %) absorption spectra for promoting plant growth. This study not only provides detailed guidelines for evaluating the practical usability enhancing the PR to PFR conversion of Ca2InTaO6:0.006Mn4+, but also presents a thorough examination of the luminescent characteristics demonstrated by the Mn4+ activators.