NaGd(MoO4)2 nanocrystals with diverse morphologies: controlled synthesis, growth mechanism, photoluminescence and thermometric properties

Abstract

Pure tetragonal phase, uniform and well-crystallized sodium gadolinium molybdate (NaGd(MoO4)2) nanocrystals with diverse morphologies, e.g. nanocylinders, nanocubes and square nanoplates have been selectively synthesized via oleic acid-mediated hydrothermal method. The phase, structure, morphology and composition of the as-synthesized products are studied. Contents of both sodium molybdate and oleic acid of the precursor solutions are found to affect the morphologies of the products significantly, and oleic acid plays a key role in the morphology-controlled synthesis of NaGd(MoO4)2 nanocrystals with diverse morphologies. Growth mechanism of NaGd(MoO4)2 nanocrystals is proposed based on time-dependent morphology evolution and X-ray diffraction analysis. Morphology-dependent down-shifting photoluminescence properties of NaGd(MoO4)2: Eu3+ nanocrystals, and upconversion photoluminescence properties of NaGd(MoO4)2: Yb3+/Er3+ and Yb3+/Tm3+ nanoplates are investigated in detail. Charge transfer band in the down-shifting excitation spectra shows a slight blue-shift, and the luminescence intensities and lifetimes of Eu3+ are decreased gradually with the morphology of the nanocrystals varying from nanocubes to thin square nanoplates. Upconversion energy transfer mechanisms of NaGd(MoO4)2: Yb3+/Er3+, Yb3+/Tm3+ nanoplates are proposed based on the energy level scheme and power dependence of upconversion emissions. Thermometric properties of NaGd(MoO4)2: Yb3+/Er3+ nanoplates are investigated, and the maximum sensitivity is determined to be 0.01333 K−1 at 285 K.

Synthesis, functionalization and properties of uniform europium-doped sodium lanthanum tungstate and molybdate (NaLa(XO4)2, X = Mo,W) probes for luminescent and X-ray computed tomography bioimaging

“…where tf represents the time required for the luminescence signal to reach the background, are also included in Table 4. It is important to mention that these values (from 1106 to 959 s, for the Eu:NaLa(WO4)2 samples; and from 861 to 655 s, for the Eu:NaLa(MoO4)2 samples) are much higher than those previously reported for these systems (from 401 to 640 s, for Eu:NaLa(WO4)2 [19, 21, 26, 41,] and from 400 to 620 s, for Eu:NaLa(MoO4)2 [42,43]). This finding seems to indicate the higher efficiency of our nanophosphors.…”

Optical fibre thermometry using ratiometric green emission of an upconverting nanoparticle-polydimethylsiloxane composite

“…Furthermore, such RE 3+ ions based on UC typically exhibit large anti-Stokes shifts [14], sharp emission lines [15] and temperature-dependent emissions, provided the two radiative energy levels have an energy difference of between 200 cm -1 and 2000 cm -1 [16][17][18]. The populations of these thermally coupled levels (TCL), related through the Boltzmann distribution, provide a natural ratiometric temperature detection approach, in that way reducing the influence of external conditions on the sensor performance and creating an inbuilt 'reference' channel [19][20][21][22].…”

Efficient up-conversion in Yb:Er:NaT(XO4)2 thermal nanoprobes. Imaging of their distribution in a perfused mouse

“…The present work is motivated by recent reports of large UC ratiometric thermal sensitivity ( S ) in four members of the MT(XO 4 ) 2 (M = Li + , Na + or Ag + , T = Y 3+ , Bi 3+ or any trivalent lanthanide Ln 3+ , and X = Mo 6+ or W 6+ ) tetragonal double molybdate (DMo) and double tungstate (DW) compound family: 10at%Yb:1at%Er:NaY(WO 4 ) 2 , S (317 K) = 112×10 −4 K -1 ;[27] 40at%Yb:2at%Er:AgLa(MoO 4 ) 2 , S (317 K) = 120×10 −4 K -1 ;[28] 5at%Yb:2at%Er:NaY(MoO 4 ) 2 , S (317 K) = 77×10 −4 K -1 ;[29] and 10at%Yb:1at%Er:NaGd(MoO 4 ) 2 , S (317 K) = 160×10 −4 K -1 ,[30] in comparison with the value reported for 20at%Yb:2at%Er:β-NaYF 4 , S (317 K) = 35×10 −4 K -1 . [31]…”

“…Only in NaGd(MoO 4 ) 2 ,[30] 50x50 nm 2 square sheets have been studied. These works show a significant spread of the reported S values which could be associated to the difference in material composition or to different experimental characterization techniques used in the involved laboratories.…”

“…On the other hand, two of the previously cited works, NaY(WO 4 ) 2 [ 27 ] and NaY(MoO 4 ) 2 [ 29 ] deal with micrometric sized materials, while in a third, AgLa(MoO 4 ) 2 ,[ 28 ] the morphology is unknown. Only in NaGd(MoO 4 ) 2 ,[ 30 ] 50x50 nm 2 square sheets have been studied. These works show a significant spread of the reported S values which could be associated to the difference in material composition or to different experimental characterization techniques used in the involved laboratories.…”