Alkali metal impact on structural and phonon properties of Er³⁺ and Tm³⁺ co-doped MY(WO₄)₂ (M = Li, Na, K) nanocrystals

Abstract

TEM images of NaY(WO4)2:Er, Tm nanocrystalline powders synthesized by the Pechini method after calcination at (a) 550 °C, (b) 600 °C and (c) 700 °C.

Effect of the Size and Shape of Ho, Tm:KLu(WO4)2 Nanoparticles on Their Self-Assessed Photothermal Properties

“…Lately, another microwave-assisted hydrothermal synthesis method for the preparation of monoclinic KY(WO 4 ) 2 nanocrystals without using organic surfactants, has been proposed [ 50 ]. This reaction involves preheating at 388 K for 0.5 h, a reaction at 523 K for 3 h, a purification process with deionized water, and a drying process at 353 K for 20 h, after calcination at 1023 K for 1 h. The final product of the reaction shows a tendency towards agglomeration and irregular morphological habits.…”

Fabrication and characterization of rubidium ferrites by the solution‐based combustion method using diverse organic fuels

“…[7][8][9][10][11][12][13] In recent times, nanosized alkali metal ferrites have attracted increasing interest, as they exhibit distinct properties compared to their bulk counterparts with the same composition. [14][15][16][17] The synthesis of nanoparticles with controlled size, shape, and composition holds immense scientific and technological significance, promising groundbreaking advancements in various nanotechnology and medical fields. [18][19][20] Consequently, an emphasis on methodological aspects becomes crucial for the design and preparation of ferrite materials.…”

NaLaW2O7(OH)2(H2O): Crystal Structure and RE3+ Luminescence in the Pristine and Annealed Double Tungstates (RE = Eu, Tb, Sm, and Dy)

“…The rare-earth (RE) double tungstates of ARE­(WO 4 ) 2 (A = alkali metal ion) initially attracted attention for solid laser applications in the single-crystal form, because of their excellent mechanical, thermal, and chemical durability, the high value of the χ­( 3 ) nonlinear cubic susceptibility, their good Raman activity, the facile admittance of various RE 3+ activators, and the broad optical transparency from the visible to the near-infrared region. − Later studies revealed that ARE­(WO 4 ) 2 tungstates (RE = La, Y, Gd, and Lu) are attractive hosts for luminescent purposes, , because these RE 3+ ions do not have absorption or emission in the visible light region and the compounds present self-activation of the WO 4 2– ligands, high optical absorption in the ultraviolet (UV) region, and efficient energy transfer from WO 4 2– to the activator. − The potential application of ARE­(WO 4 ) 2 has been demonstrated in the multifaceted areas of bioimaging [PEG-NaGd­(WO 4 ) 2 :Eu], biosensors [Na­(Gd,Eu)­(WO 4 ) 2 ], photothermal therapy (PTT) [NaY­(WO 4 ) 2 :Sm 3+ /Nd 3+ ], photocatalysis, light-emitting diodes (LEDs) [NaGd­(WO 4 ) 2 :Pr 3+ ], and temperature sensing [NaY­(WO 4 ) 2 :Er 3+ /Yb 3+ ] …”

“…The synthesis of ARE­(WO 4 ) 2 compounds can be achieved by a number of methodologies, including solid-state reaction, sol–gel and Pechini-type sol–gel, molten salt growth, microwave-assisted processing , and hydrothermal/solvothermal reaction, , as also summarized in the review article by Kaczmarek and van Deun . Though the hydrothermal and solvothermal techniques are widely acknowledged to be capable of directly generating inorganic solids of controlled phase structure and crystallite morphology within a short amount of reaction time, they frequently yielded unknown products (precursors) for the RE 3+ –tungstate reaction system.…”

“…As a result, subsequent annealing is needed to convert the precursor into the targeted ARE­(WO 4 ) 2 :Ln compound (A = Na and K; RE = La, Y, Gd, and Lu; Ln = Eu 3+ , Tb 3+ , Sm 3+ , Dy 3+ , and Sm 3+ /Nd 3+ ; etc. ). ,,, This is primarily due to the rich solution chemistry of tungstate anions, which present themselves as monomeric [WO 4 ] 2– in a solution of sufficiently high alkalinity (pH >8), while the various protonated and polymerized forms of [H 18 (WO 4 ) 12 ] 6– , [H 10 (WO 4 ) 6 ] 2– , [H 7 (WO 4 ) 6 ] 5– , and [HWO 4 ] − appear in an acidic or neutral solution (pH 4–7). − Furthermore, the type and concentration of tungstate ions are affected by not only the solution pH but also the temperature, the initial concentration of the tungstate source (such as Na 2 WO 4 ·2H 2 O in this work), and the attendance and concentration of alien anions. On the other hand, RE 3+ undergoes hydration and hydrolysis in an aqueous solution to form [RE­(OH) x (H 2 O) y ] 3– x complex ions, whose x value increases with an increase in the solution pH. , Numerous reaction pathways are, therefore, possible under hydrothermal/solvothermal conditions, which, in turn, make the product rather sensitive to the synthesis parameter. ,, It was recently shown that the reactivity of tungstate species toward [RE­(OH) x (H 2 O) y ] 3– x decreases with an increase in solution pH, and the hydrothermal product of a higher pH tends to have a lower W/RE molar ratio and vice versa. , The complicated solution chemistry and reaction pathway may account for why most of the studies to date left the hydrothermal/solvothermal precursors unanalyzed for chemical composition, phase purity, phase constituent, and phase structure.…”