Luminescence of Mn⁴⁺ activated Li₄Ti₅O₁₂

This work demonstrates the luminescence of Mn⁴⁺ activated cubic spinel Li₄Ti₅O₁₂ (LTO) powders. One-step solid-state method was used to obtain eleven samples with different quantities of Mn⁴⁺. The deep red emission centered at around 696 nm originates from ²E_g → ⁴A_2g spin forbidden electronic transitions from 3 d³ electron configuration of Mn⁴⁺ ion. The concentration quenching of emission is also observed in values of excited-state lifetimes, ranging from 212 μs to 143 μs. Such emission in the red spectral region which can be excited by blue light is suitable for the plant growth LEDs. The exchange charge model (ECM) of crystal field was used to calculate the Mn⁴⁺ energy levels in the LTO host. The temperature dependence of the Mn⁴⁺ emission in LTO was measured in the 10–350 K temperature range. Excited-state lifetime strongly changes with temperature. A very large value of relative sensitivity of 2.6% K⁻¹ is found at 330 K, which facilitates temperature measurements with the temperature resolution of about 0.26 K. A low concentration of Nb⁵⁺ co-doping sensitizes the Mn⁴⁺ optical center effectively showing a relative increment of emission intensity.