Micro- and nanosized architectures in hydrothermal Tm3+-doped GdVO4: chemical insights towards preservation of the emission efficiency

Abstract

Chemical processes involving low temperature hydrothermal treatment of pH 4, 7 and 10 solutions of Gd(Tm)-nitrates or chlorides and NH₄VO₃ result in the formation of crystalline nanorods, nanotubes, nanoribbons, nanospindles and 3D micro- or nanoparticles of Tm-doped zircon-type GdVO₄. The relationship between these morphologies and both the structure of the V⁵⁺-precursor in the solution, which depends on the pH, and the hydrothermal treatment has been established. The prepared Tm-GdVO₄ shows excitation (³H₆ → ³H₄) and photoluminescence (³F₄ → ³H₆) spectra of Tm³⁺ involved in the ∼1.85 to 2.05 μm laser emission similar to those in single crystals. Room temperature luminescence decays of these excited states exhibit single exponential dynamics for ³F₄ in the lowest Tm³⁺-doped materials, and mostly nonexponential behavior for ³H₄ and ³F₄ in Tm³⁺ concentrated samples, which has been analytically reproduced by the sum of two exponential regimes ascribed to the different rates of nonradiative relaxations in defects at the surface and in the core of the nanocrystals. ³H₄ and ³F₄ fluorescence lifetimes evolve in the sequence τ_pH10 < τ_pH4 < τ_pH7, and highest values τ (³H₄) = 155 μs and τ (³F₄) = 990 μs for 0.2 at% Tm³⁺ materials are very close to the radiative lifetimes for Tm³⁺ in the GdVO₄ crystal, τ_RAD = 174 μs and τ_RAD = 1036 μs, respectively.