Magical polyhedral twist via chemical unit co-substitution in LaAlO3:Mn4+ to greatly enhance the zero phonon line for high-efficiency plant-growth LEDs

Phytochrome and phytochrome-controlled physiological responses play an important role in plant growth. The emission of LaAlO3:Mn4+ partly matches with the absorption spectrum of the P-FR region. However, the luminescence efficiency is not high due to the discontinuous emission spectrum, thus resulting in its limited application prospects in plant-growth LEDs. Here, new phosphors of LaAl0.999-x(Mg/Ge)(x)O-3:0.001Mn(4+) (LAMG:Mn4+, x = 0-0.4) were successfully synthesized via a solid-state reaction. Through a promising strategy of chemical unit co-substitution, that is substituting Mg2+-Ge4+ for Al3+-Al3+, a significant octahedral tilting distortion and a decreased symmetry of MnO6 took place. Interestingly, the zero phonon line (ZPL) of Mn4+, located in the middle between the Stokes and the anti-Stokes vibronic bands, appeared and became stronger with an increase of the x value from 0 to 0.4. This makes the emission peak become a continual broad band with a FWHM of similar to 50 nm, instead of two original separate ones, thus inducing a high absorption efficiency of the phytochrome. The electroluminescence spectrum of the LED prepared using commercial red phosphors CaAlSiN3:Eu2+ and LaAl0.599(Mg/Ge)(0.4)O-3:0.001Mn(4+) matched well with P-R and P-FR, indicating that LaAl0.599(Mg/Ge)(0.4)O-3:0.001Mn(4+) can be used as a near-infrared component in phosphor-converted LEDs for controlling plant growth.

Automated summary

New phosphors were successfully synthesized through a strategy of chemical unit co-substitution, which improved the spectral properties of Mn4+ and increased the absorption efficiency, showing potential application in plant growth LEDs.