Synthesis, Crystal Structure and Photoluminescent Properties of Red-Emitting CaAl4O7:Cr3+ Nanocrystalline Phosphor

Abstract

Calcium dialuminate, CaAl4O7, nanopowders with a grossite-type structure, doped with chromium ions, were synthesized via the combined sol–gel solution combustion method. The evolution of phase composition, crystal structure, and microstructural parameters of the nanocrystalline materials depending on the temperature of the thermal treatment was investigated via X-ray powder diffraction and applying the Rietveld refinement technique. The photoluminescent properties of CaAl4O7 nanophosphors activated with Cr3+ ions were studied over the temperature range of 4.5–325 K. The samples show deep red and near-infrared luminescence due to the 2E → 4A2 and 4T2 → 4A2 energy level transitions of Cr3+ ions under excitation in the two broad emission bands in the visible spectral region. The R lines emission reveals a strong temperature dependence. The feasibility of the material for non-contact luminescence sensing is investigated, and good sensitivity is obtained based on the (R2/R1) luminescence intensity ratio and the lifetime of the emission.

Evaluation of Li2SnO3:Cr3+, Mn4+ as a dual-emitter luminescence sensor for cryogenic temperatures

“…It is pertinent to remark that incorporation of TM ions at different crystallographic sites is a common feature observed in complex oxides. 26–28…”

“…It is pertinent to remark that incorporation of TM ions at different crystallographic sites is a common feature observed in complex oxides. [26][27][28] The observed temperature dependencies offer insight into the dynamics governing the population of excited states within the emission centres under consideration. To attain a more comprehensive understanding of this behaviour, we examined the normalized intensity of various emissions, presented as a function of temperature (see Fig.…”

“…The change of decay time constant of the R-lines is yet another feature of emission of TM ions that is regularly applied for temperature monitoring. 26,[37][38][39] To verify the merit of these characteristics we measured the variation of luminescence decay time constants of the R-lines in Li 2 SnO 3 . Fig.…”