Crystallization of RE2(OH)2CO3SO4·nH2O as a new family of layered hydroxides (RE = Gd−Lu lanthanides and Y), derivation of RE2O2SO4, photoluminescence and optical thermometry

Abstract

Layered rare-earth hydroxides (LREHs) draw wide research interest because of their peculiar crystal structure, rich interlayer chemistry and abundant functionality of the RE element, but are limited to the two categories of RE2(OH)5A·nH2O (A: typical of Cl− or NO3−) and RE2(OH)4SO4·nH2O. On the other hand, rare-earth oxysulfates (RE2O2SO4) have attracted attention due to their properties of large-capacity oxygen storage, low-temperature magnetism and luminescence, but their preparation procedure mostly involves toxic SOx gases and/or complicated procedures. In this work, RE2(OH)2CO3SO4·nH2O as a new family of LREHs (RE = Gd‒Lu lanthanides and Y) were produced via hydrothermal reaction, from which phase-pure RE2O2SO4 was derived via subsequent annealing at 800 °C in air without the involvement of SOx. The compounds were thoroughly characterized to reveal the intrinsic influence of lanthanide contraction (RE3+ radius) on crystal structure, thermal behavior (dehydroxylation/decarbonation/desulfurization), vibrational property and crystallite morphology. Through analyzing the photoluminescence of Eu3+ and Sm3+ in the Gd2O2SO4 typical host it is found that the 617 nm (Eu3+, λex = 275 nm) and 608 nm (Sm3+, λex = 407 nm) main emissions can retain as high as ∼79.6% and 85.5% of their room-temperature intensities at 423 K, with activation energies of ∼0.19 and 0.21 eV for thermal quenching, respectively. Application also indicates that both the phosphors have the potential for optical temperature sensing via the fluorescence intensity ratio (FIR) technology, whose maximum relative sensitivity reaches ∼2.70%/K for Eu3+ and 1.73%/K for Sm3+ at 298 K.