Selective emission and luminescence of Er2O3 under intense laser excitation

The microstructure of Er₂O₃ polycrystals synthesised by laser heating is studied. The synthesis of erbium silicate (Er₂SiO₅) layers was observed upon interaction of Er₂O₃ and SiO₂ melts. The dependences of the selective emission (SE) and luminescence spectra of Er₂O₃ polycrystals in the range 200 – 1700 nm on the intensity of laser-thermal (at the wavelength λ = 10.6 μm) and resonant laser (λ ≈ 975 nm) excitation are investigated. The emission of heated Er₂O₃ polycrystals arises as a result of multiphonon relaxation of absorbed energy and is a superposition of the SE at the electronic-vibrational transitions of Er³⁺ ions and the thermal radiation of the crystal lattice. The shape of the SE spectra of Er₂O₃ polycrystals in the range 400 – 1700 nm almost does not change upon laser-thermal heating from 300 to 1500 K and subsequent cooling and corresponds to the absorption spectra of Er³⁺ ions. With increasing temperature, the thermal radiation intensity increases faster than the SE intensity, and the shape of the Er₂O₃ spectrum becomes closer to the calculated spectrum of a blackbody. The anti-Stokes luminescence spectra of Er³⁺ ions formed under intense laser excitation of the ⁴I_11/2 level are explained by additional SE caused by heating of the crystal matrix due to the Stokes losses. A difference between the SE and luminescence spectra is observed at low intensities of resonant laser excitation and low temperatures, when only the Stokes luminescence occurs. The temperature dependences of the SE and luminescence spectra of Er₂O₃ upon laser excitation testify to the fundamental role played by the interaction of the electronic f-shell of Er³⁺ ions with crystal lattice vibrations in the processes of multiphonon radiative and nonradiative relaxation. The laser-thermal synthesis is promising for inprocess variation of the chemical composition of rare-earth samples.