KLn(MoO₄)₂ micro/nanocrystals (Ln = La–Lu, Y): systematic hydrothermal crystallization, structure, and the performance of doped Eu³⁺ for optical thermometry

Abstract

KLn(MoO4)2 has structure/morphology preference toward the size of Ln3+. The 5D0 and 5D1 energy levels of Eu3+ in layered KY(MoO4)2 showed an excellent performance in optical thermometry.

Systematic Crystallization of NH4Ln(MoO4)2 as a Family of Layered Compounds (Ln = La–Lu and Y), Derivation of Ln2Mo4O15, Crystal Structure, and Photoluminescence

“…The ( 5 D 0 → 7 F 2 )/( 5 D 0 → 7 F 1 ) intensity ratio (R/O value) was assayed to be ∼15.2, indicating that the compound has a high-purity red emission. Besides, the R/O value is higher than those of some molybdate/tungstate phosphors reported in the literature, such as 5 atom % Eu 3+ -doped LiLa(MoO 4 ) 2 (R/O ∼ 7.7), 38 1 atom % Eu 3+ -doped NaY(MoO 4 ) 2 (R/O ∼ 7.4), 39 KEu(MoO 4 ) 2 (R/O ∼ 10.5), 20 and NaEu(WO 4 ) 2 (R/O ∼ 10.4). 40 This implies that Eu 3+ has a lower symmetry in NH 4 Eu(MoO 4 ) 2 .…”

“…Though our thorough literature survey failed to find a general strategy for Ln 2 Mo 4 O 15 synthesis, ALn­(MoO 4 ) 2 double molybdates (A = alkali; Ln = La–Lu lanthanide and Y), such as NaLn­(MoO 4 ) 2 and KLn­(MoO 4 ) 2 , − can nevertheless be systematically obtained by applying the hydrothermal reaction. It was analyzed that the Na group was crystallized in the tetragonal system for the larger Ln 3+ of Ln = La–Dy and in the orthorhombic system for the smaller Ln 3+ of Ln = Ho–Lu and Y, while the K-group is monoclinic for Ln = La, tetragonal for Ln = Ce, and orthorhombic for Ln = Pr–Lu and Y.…”

Extensive tailoring of REPO4 and REVO4 crystallites via solution processing and luminescence

“…Therefore, REPO 4 can be preferentially precipitated out in a wide range of solution pH and even in the presence of many other types of anions. 49 The solution chemistry of vanadate ion is remarkably more complicated than that of its phosphate counterpart due to protonation and polymerization to form polyoxoanion, as in the cases of tungstate/molybdate ions, [50][51][52] 46,53,54 In addition, reduction of V 5+ to V 4+ may occur during a hydrothermal/solvothermal reaction in some cases, which deteriorates the luminescence of the doped Ln 3+ activator. [55][56][57] If VO 4 3− is considered as the direct anion for precipitation reaction, it can then be inferred from the above that a sufficiently alkaline condition would favor REVO 4 formation, although the compound may be formed via neutralization of [RE(OH) x (A m ) n (H 2 O) y ] 3−x−mn cations (a base) with protonated vanadate species (an acid).…”

“…Therefore, REPO 4 can be preferentially precipitated out in a wide range of solution pH and even in the presence of many other types of anions. 49 The solution chemistry of vanadate ion is remarkably more complicated than that of its phosphate counterpart due to protonation and polymerization to form polyoxoanion, as in the cases of tungstate/molybdate ions, 50–52 and the dominant type of vanadate species is also substantially affected by the concentration of vanadate ions itself, temperature and alien anions. The following types of vanadate species have been reported in the literature: [VO 2 (H 2 O)] + and V 2 O 5 for pH ≤2, H 3 VO 4 and [H 2 V 10 O 28 ] 4− for pH 2–4, H 2 VO 4 − , [V 4 O 12 ] 4− and [HV 10 O 28 ] 5− for pH 4–9, and VO 4 3− , HVO 4 2− and [V 2 O 7 ] 4− for pH 9–12.…”

Multisignal optical temperature‐sensing properties of Eu3+‐doped NaYF4 nanoparticles

“…Although Eu 3+ is a kind of frequently‐used RE 3+ ions for its strong red emissions of 5 D 0 → 7 F J , there are only a few reports of optical temperature sensing using the FIR of Eu 3+ , [ 16–21 ] because the other emissions except 5 D 0 → 7 F J (typically 5 D 1 → 7 F J’ ) are usually too weak to be detected in many kinds of hosts. [ 22–24 ] Furthermore, these few reports focused on temperature sensing in high temperature range are based on thermal excitation between thermal coupled levels (TCLs) of 5 D 0 and 5 D 1 .…”