Samarium(iii) and terbium(iii) ion-doped NaLa(MoO4)2 phosphors for versatile applications

Abstract

Trivalent samarium (Sm³⁺) and terbium (Tb³⁺) ion single- and co-doped sodium lanthanum molybdate [NaLa(MoO₄)₂] phosphors were successfully synthesized by a citric acid-assisted sol–gel method. The single- and co-doped compounds exhibited a tetragonal phase with the space group of I4₁/a based on the X-ray diffraction pattern. The room-temperature photoluminescence (PL) study revealed the characteristic emission properties of the Sm³⁺ and Tb³⁺ ions in the reddish-orange and green regions, respectively. In the thermal study, the PL emission intensity of the optimized NaLa(MoO₄)₂:0.03Sm³⁺ phosphor at 423 K reached 83.73% when compared with its initial value at 303 K; this implies that this phosphor has excellent thermal stability. In addition, the packaged light-emitting devices with Sm³⁺ and Tb³⁺ single-doped phosphors emitted red and green lights, respectively. For the Sm³⁺/Tb³⁺ co-doped NaLa(MoO₄)₂ phosphors, tunable emissions from green-yellow to red with a good energy transfer mechanism were observed. Similarly, the temperature sensing properties of Sm³⁺/Tb³⁺ co-doped NaLa(MoO₄)₂ phosphors were investigated by the fluorescence intensity ratio technique, and their absolute sensor sensitivity reached 0.02 K⁻¹ at 443 K, whereas the relative sensor sensitivity was calculated to be 0.68% K⁻¹. Furthermore, the packaged light-emitting devices based on the optimized NaLa(MoO₄)₂:0.13Tb³⁺/0.015Sm³⁺ phosphor emitted a warm white light, and the corresponding color-rendering index and correlated color temperature values were 89.76 and 2656 K, respectively.