The pH-dependent reactions in the sonochemical synthesis of luminescent fluorides: The quest for the formation of KY₃F₁₀ crystal phases

Highlights

• We reveal the significance of sonochemistry in the design of luminescent fluorides.

• The study offers the key to synthesizing both the α- and δ-phases of KY₃F₁₀.

• A landmark methodology for the preparation of yttrium hydroxyfluorides is reported.

• The reaction mechanisms underlying the formation of the compounds are unraveled.

• The Eu³⁺-doping endows the materials with highly tunable optical properties.

Abstract

In this study Eu³⁺-doped yttrium fluorides were designed by ultrasound-assisted processes at different pH values (4.0–9.0). This novel strategy has enabled to obtain materials with intriguing morphologies and modulated crystal structures: α-KY₃F₁₀, δ–KY₃F₁₀·xH₂O, and Y(OH)_3–xF_x. To date, the literature has primarily focused only on the α-phase of KY₃F₁₀. Yet, explaining the formation of the mostly uncharted δ-phase of KY₃F₁₀ remains a challenge. Thus, this paper offers the key to synthesizing both the α and the δ-phases of KY₃F₁₀ and also reports the first ultrasound-assisted process for the preparation of yttrium hydroxyfluorides. It is also unraveled the connection between the different pH-dependent reactions and the formation mechanisms of the compounds. In addition to this, the unique features of the Eu³⁺ ion have allowed to conduct a thorough study of the different materials and have endowed the compounds with photoluminescent properties. The results underscore a highly tunable optical response, with a wide gamut of color emissions (from orangish to red hues), lifetimes (from 7.9 ms to 1.1 ms) and quantum efficiencies (98–28%). The study unveils the importance of sonochemistry in obtaining luminescent fluorides with controlled crystal structures that can open up new avenues in the synthesis and design of inorganic materials.