Photoluminescence and optical properties of Eu3+/Eu2+-doped transparent Al2O3 ceramics

Transparent Eu3+-doped (0.05-0.15 at. %) alumina ceramics with fine-grained microstructure were prepared and studied in terms of optical properties and photoluminescence (PL). The light transmission through ceramics up to dopant concentrations 0.125 at. % is dominated by birefringence scattering at grain boundaries. As confirmed by HRTEM/EDS element mapping, high photoluminescence intensity was achieved as the result of the dopant segregation at grain boundaries. The PL emission spectra of Al2O3:Eu3+ ceramics exhibited red light emissions with the highest intensity (394 nm excitation) for material containing 0.125 at. % of Eu3+. The luminescence decay was single-exponential with a lifetime similar to 1.5 ms. The post-sintering reduction of Eu3+-Eu2+ under an H-2 atmosphere (at 1300 degrees C) was difficult. Two simultaneously coexisting Eu2+ emitting PL centers were identified, one emitting blue light with average decay constant of 150 ns, and the other green light (more intense) with average decay constant of 1.3 mu s.

Automated summary

Transparent Eu3+-doped alumina ceramics with fine-grained microstructure were studied for their optical properties and photoluminescence. It was found that light transmission through ceramics at high dopant concentrations is dominated by birefringence scattering at grain boundaries, while high photoluminescence intensity is achieved as a result of dopant segregation at grain boundaries. Luminescence decay in these ceramics was single-exponential with a lifetime around 1.5 ms, and the reduction of Eu3+ to Eu2+ under H2 atmosphere was challenging post-sintering. Additionally, two coexisting Eu2+ emitting PL centers were identified, emitting blue and green light with different decay constants.