Exploring the Impact of Structure-Sensitivity Factors on Thermographic Properties of Dy 3+ -Doped Oxide Crystals.

Optical absorption spectra and luminescence spectra were recorded as a function of temperature between 295 K and 800 K for single crystal samples of Gd ₂ SiO ₅ :Dy ³⁺ , Lu ₂ SiO ₅ :Dy ³⁺ , LiNbO ₃ :Dy ³⁺ , and Gd ₃ Ga ₃ Al ₂ O ₁₂ :Dy ³⁺ fabricated by the Czochralski method and of YAl ₃ (BO ₃ ) ₄ :Dy ³⁺ fabricated by the top-seeded high temperature solution method. A thermally induced change of fluorescence intensity ratio (FIR) between the ⁴ I _15/2 → ⁶ H _15/2 and ⁴ F _9/2 → ⁶ H _15/2 emission bands of Dy ³⁺ was inferred from experimental data. It was found that relative thermal sensitivities S _R at 350 K are higher for YAl ₃ (BO ₃ ) ₄ :Dy ³⁺ and Lu ₂ SiO ₅ :Dy ³⁺ than those for the remaining systems studied. Based on detailed examination of the structural peculiarities of the crystals it was ascertained that the observed difference between thermosensitive features cannot be attributed directly to the dissimilarity of structural factors consisting of the geometry and symmetry of Dy ³⁺ sites, the number of non-equivalent Dy ³⁺ sites, and the host anisotropy. Instead, it was found that a meaningful correlation between relative thermal sensitivity S _R and rates of radiative transitions of Dy ³⁺ inferred from the Judd-Ofelt treatment exists. It was concluded that generalization based on the Judd-Ofelt parameters and luminescence branching ratio analysis may be useful during a preliminary assessment of thermosensitive properties of new phosphor materials.