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 E_g = 3.526 eV. With a 367 nm excitation, the Mn⁴⁺-doped Ca₂InTaO₆ exhibits a far-red emission at 689 nm, corresponding to the ²E_1g to ⁴A_2g transition. The photoluminescence (PL) characteristics of the sample align well with the absorption properties of phytochrome far-red light (P_FR). Based on analysis using the Tanabe-Sugano diagram, it can be inferred that Mn⁴⁺ is situated in a highly intense crystalline field for the ²E_1g 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 P_FR (85.68 %) than P_R (22.27 %) absorption spectra for promoting plant growth. This study not only provides detailed guidelines for evaluating the practical usability enhancing the P_R to P_FR conversion of Ca₂InTaO₆:0.006Mn⁴⁺, but also presents a thorough examination of the luminescent characteristics demonstrated by the Mn⁴⁺ activators.