Luminescence of Mn4+ activated Li4Ti5O12

Abstract

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 2Eg → 4A2g 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.