Crystallization of RE_(2)(OH)_(2)CO_(3)SO_(4)·nH_(2)O as a new family of layered hydroxides(RE=Gd-Lu lanthanides and Y),derivation of RE_(2)O_(2)SO_(4),photoluminescence and optical thermometry

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 RE_(2)(OH)_(5)A·nH_(2)O(A:typical of Cl^(-)or NO_(3)^(-)) and RE_(2)(OH)_(4)SO_(4)·nH_(2)O.On the other hand,rare-earth oxysulfates(RE_(2)O_(2)SO_(4)) have attracted attention due to their properties of large-capacity oxygen storage,low-temperature magnetism and luminescence,but their preparation procedure mostly involves toxic SO_(x) gases and/or complicated procedures.In this work,RE_(2)(OH)_(2)CO_(3)SO_(4)·nH_(2)O as a new family of LREHs(RE=Gd-Lu lanthanides and Y) were produced via hydrothermal reaction,from which phase-pure RE_(2)O_(2)SO_(4) was derived via subsequent annealing at 800℃ in air without the involvement of SO_(x),The compounds were thoroughly characterized to reveal the intrinsic influence of lanthanide contraction(RE^(3+) radius) on crystal structure,thermal behavior(dehydroxylation/decarbonation/desulfurization),vibrational property and crystallite morphology.Through analyzing the photoluminescence of Eu^(3+) and Sm^(3+)in the Gd_(2)O_(2)SO_(4) typical host it is found that the 617 nm(Eu^(3+),λ_(ex)=275 nm) and 608 nm(Sm^(3+),λ_(ex)=407 nm) main emissions can retain as high as ^(7)9.6% 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 Eu^(3+)and 1.73%/K for Sm^(3+) at 298 K.