Controlled processing of (Gd,Ln)₂O₃:Eu (Ln = Y, Lu) red phosphor particles and compositional effects on photoluminescence

Abstract

Synthesis of (Gd0.95−xLnxEu0.05)2O3 (Ln = Y and Lu, x = 0–0.95) powders via ammonium hydrogen carbonate (AHC) precipitation has been systematically studied. The best synthesis parameters are found to be an AHC/total cation molar ratio of 4.5 and an ageing time of 3 h. The effects of Y3+ and Lu3+ substitution for Gd3+, on the nucleation kinetics of the precursors and structural features and optical properties of the oxides, have been investigated. The results show that (i) different nucleation kinetics exist in the Gd–Y–Eu and Gd–Lu–Eu ternary systems, which lead to various morphologies and particle sizes of the precipitated precursors. The (Gd,Y)2O3:Eu precursors display spherical particle morphologies and the particle sizes increase along with more Y3+ addition. The (Gd,Lu)2O3:Eu precursors, on the other hand, are hollow spheres and the particle sizes increase with increasing Lu3+ incorporation, (ii) the resultant oxide powders are ultrafine, narrow in size distribution, well dispersed and rounded in particle shape, (iii) lattice parameters of the two kinds of oxide solid solutions linearly decrease at a higher Y3+ or Lu3+ content. Their theoretical densities linearly decrease with increasing Y3+ incorporation, but increase along with more Lu3+ addition and (iv) the two kinds of phosphors exhibit typical red emissions at ∼613 nm and their charge-transfer bands blue shift at a higher Y3+ or Lu3+ content. Photoluminescence/photoluminescence excitation intensities and external quantum efficiency are found to decrease with increasing value of x, and the fluorescence lifetime mainly depends on the specific surface areas of the powders.

Recent progress in advanced optical materials based on gadolinium aluminate garnet (Gd3Al5O12)

“…The [(Gd 0.7 Lu 0.3 ) 0.95 Eu 0.05 ]AG phosphor synthesized at 1500 °C has internal/external quantum efficiencies (%) of 83.2/56.1, an asymmetry factor of ∼2.85, and a fluorescence lifetime of ∼4.1 ms for the 591 nm emission [31]. The lifetime is close to that (4.66 ms) reported for YAG:Eu [35] but is significantly longer than those (generally 0.5–2.5 ms) of the well-known red phosphors of Y 2 O 3 :Eu [36, 37], (Gd 1− x Ln x ) 2 O 3 :Eu (Ln = Y, Lu) [22, 38], and La 2 O 2 S:Eu [39], since the Eu 3+ activator takes the highly symmetric D 2 lattice site in garnet. Increasing Lu incorporation up to x = 0.5 would lower excitation/emission and also blue-shift the CTB due to gradually decreased covalency of the host lattice ( χ = 1.27 for Lu 3+ ), for which a minimized Lu content was recommended as long as the garnet lattice can be effectively stabilized [31].…”

“…Increasing Lu incorporation up to x = 0.5 would lower excitation/emission and also blue-shift the CTB due to gradually decreased covalency of the host lattice ( χ = 1.27 for Lu 3+ ), for which a minimized Lu content was recommended as long as the garnet lattice can be effectively stabilized [31]. Similar phenomena were observed in the development of (Gd 1− x Ln x ) 2 O 3 :Eu red phosphors (Ln = Y, Lu) [38]. Compared with YAG:Eu, the GAG-based phosphor (figure 7) has an additional excitation band arising from the 8 S 7/2 → 6 I J Gd 3+ transition at ∼275 nm (significantly stronger than the strongest 7 F 0,1 → 5 L 6 intra-4f 6 transition of Eu 3+ at ∼395 nm), suggesting substantial energy migration from Gd 3+ to Eu 3+ .…”

Glycine–Nitrate Process for the Elaboration of Eu3+‐Doped Gd2O3 Bimodal Nanoparticles for Biomedical Applications

“…Recent research has demonstrated that gadolinium oxide (Gd 2 O 3 ) nanoparticles can act as T 1 CAs to remarkably enhance MRI signal intensity owing to the increased availability of Gd 3+ ions at their surface to interact with water. [30][31][32][33][34] The synthesis of such nanosized particles can be performed by various methods such as the polyol, [35] sol lyophilization, [36] sol-gel, [37] precipitation, [38][39][40] hydro/ solvothermal, [41][42][43] sonochemistry, [44] spray pyrolysis, [45,46] and aqueous self-combustion methods. [46][47][48] Aqueous selfcombustion can be the most appropriate synthesis route as it can yield high-phase-purity powder with excellent chemical homogeneity.…”

Production and optical properties of Ce3+‐activated and Lu3+‐stabilized transparent gadolinium aluminate garnet ceramics

“…The AHC solution contains various ionic species, such as , , OH − , H + , and . According to lanthanide contraction law, the Lu 3+ cation has the highest degree of hydrolysis in the lanthanide family because it has the smallest ionic radius . Therefore, the high degree of hydrolysis for Lu 3+ together with Al 3+ causes high activities of the [Lu(OH) x (H 2 O) 6− x ] 3− x and [Al(OH)(H 2 O) 5 ] 2+ species.…”

“…Figure exhibits the responses of the (Gd,Lu) 3 Al 5 O 12 :Ce phosphor powder and transparent ceramic to 457 nm excitation using a solid BaSO 4 white standard as a reference material. The external quantum efficiencies (ɛ ex ) and the internal quantum efficiencies (ɛ in ) of the two samples were automatically deduced from Equations and , respectively, via the software in the spectrophotometer:where P(λ)/hν , R(λ)/hν , and E(λ)/hν are the numbers of photons in the emission, reflectance, and excitation spectra of the samples, respectively.…”