Solid solution Na(Gd/La)(MoO4)2:Yb3+/Er3+ upconversion nanocrystals with simultaneously enhanced photothermal conversion efficiency and luminescence intensity

Abstract

Lanthanide doped upconversion nanocrystals with remarkable optical properties have been utilized for many emerging applications. Here, solid solution Na(GdxLa1-x)(MoO4)2 nanocrystals are synthesized hydrothermally, and their upconversion photoluminescent and photothermal properties as luminescent host matrix for Yb3+/Er3+ activators are systematically studied. The effect of La3+ doping content on the phase, crystal structure, upconversion luminescence and photothermal conversion are investigated. Rietveld refinements based on XRD data indicate that La3+ occupy Gd3+ sites substitutionally, and pure phase solid solution Na(GdxLa1-x)(MoO4)2 is formed. Due to lattice distortion, lower lanthanide site symmetry and augmented odd-parity crystal field interactions after La3+ doping, the 4f-4f transition probabilities of the lanthanide ions are effectively increased. Na(Gd/La)(MoO4)2 solid solution hosts exhibit enhanced upconversion luminescence from Er3+/Yb3+, compared with single-component NaGd(MoO4)2 counterparts. What's more, based on the calculated temperatures of the samples derived from the luminescence intensity ratio of states 2H11/2 and 4S3/2 for Er3+, enhanced photothermal conversion efficiency is speculated in solid solution Na(GdxLa1-x)(MoO4)2:Yb3+/Er3+ nanocrystals, which is further confirmed by infrared thermographic images. The underling mechanisms of simultaneously enhanced photothermal effects and luminescence intensity in Na(GdxLa1-x)(MoO4)2 solid solution nanocrystals are elucidated. Modulation of composition in solid solution hosts may be an effective method for combating luminescent thermal quenching and/or regulating photothermal conversion and photoluminescence properties simultaneously. Multifunctional solid solution upconversion nanocrystals could be potential for photoluminescent and photothermal applications.