One-phonon sideband and multiphonon relaxation in La1.6Mo2O9: Eu0.43+ and β-NaGdF4: Tb3+ nanocrystals

Abstract

The experimental studies of one-phonon sideband (PSB) and multiphonon relaxation (MR), involving a large energy gap (5800 cm⁻¹) crossover from bulk to a nanocrystal (NC) system are reported. Two one-phonon sidebands, PSB₁ = 449 nm and PSB₂ = 429 nm associated with the Eu^{3+ 7}F₀ → ⁵D₂ 464 nm zero phonon line (ZPL), were observed in the excitation spectra monitoring Eu^{3+ 5}D₀ → ⁷F₂ at 613 nm, which resulted from Mo–O and O–Mo–O local mode vibrations, respectively. The phonon densities of states of ρ(ω) were determined from the profile of PSB. The temperature dependence of MR rate for the Tb^{3+ 5}D₃ → ⁵D₄ in β-NaGdF₄:Tb³⁺ NCs was analyzed in a single-frequency approximation of the phonon spectrum in the framework of the nonlinear theory of MR. The experimental data were in good agreement with the theoretical curves within the range of 12 K to 312 K. It is concluded that the MR occurs predominantly via high-energy optical phonons.