Size of the rare-earth ions: a key factor in phase tuning and morphology control of binary and ternary rare-earth fluoride materials

Abstract

In an ionic liquid assisted solvothermal synthesis developed by us for the synthesis of rare-earth (RE) fluorides, it is possible to control the product formation by the choice of the rare earth ion. For rareearth cations with smaller ionic radii (below 1.075Å), cubic NaREF 4 with a spherical morphology is obtained, whilst for rare-earth cations with radii between 1.08Å and 1.13Å, the formation of hexagonal NaREF 4 with a nanorod-like morphology is observed. For rare earth ions with a larger radius than that of La 3+ (1.216Å), instead of ternary fluorides, binary fluorides REF 3 in the trigonal modification is obtained.The growth mechanism behind this morphology change is explained from atomistic origin using electron microscope studies. The lattice strain changes with the rare-earth fluoride phase. For cubic NaREF 4 a tensile strain is observed, whilst for the hexagonal and trigonal binary fluoride a compressive strain is observed. The optical properties of the obtained materials promises use for various optoelectronic applications. Scheme 1 Tuning of crystal phase and nature of product (binary/ ternary) depending on the size of the RE 3+ ions for RE-doped NaREF 4 . 33468 | RSC Adv., 2017, 7, 33467-33476 This journal is NaYbF 4 :Er 3+ nanoparticles prepared solvothermally in the presence of [C 2 mim]Br at 200 C. This journal isFig. 7 (a) Excitation spectrum of NaGdF 4 :Eu 3+ nanocrystals (l em ¼ 615 nm); (b) emission spectra of NaGdF 4 :Eu 3+ ; and (c) NaYF 4 :Eu 3+ nanocrystals measured upon excitation at 393 nm (d) CeF 3 ; as well as CeF 3 :Tb 3+ nanocrystals measured upon excitation at 270 nm. 33474 | RSC Adv., 2017, 7, 33467-33476 This journal is

Influence of ionic liquids and concentration of red phosphorous on luminescent Cu3P nanocrystals

“…On exciting the Ce 3?doped Cu 3 P NCs at 278 nm, broad emission peak around 340-380 nm appears which corresponds to 5d-4f transition of Ce 3? ion (Figure S3 a, b, Supplementary Information). 30,31 Figure 8a shows the excitation spectra of Ce 3? and Tb 3?…”

“…Appearance of peak at 278 nm is due to 4f-5d transition. 30,31 On exciting at 278 nm, normally energy transfer is taking place from Ce 3? to Tb 3? ions.…”

“…ions. 30,31 Thereafter, non-radiative decay occurs to the excited level 5 D 4 of Tb 3? ions followed by radiative decay to numerous underlying levels 7 F 0-6 of Tb 3? ions.…”

“…ion at 482, 542, 585 and 621 nm correspond to 5 D 4 -7 F 6 , 5 D 4 -7 F 5 , 5 D 4 -7 F 4 and 5 D 4 -7 F 3 transitions, respectively are found in Cu 3 P:Ce/Tb NCs (shown in Figure 8b). 30,31 The highly intense green emission is observed at 542 nm ( 5 D 4 -7 F 5 transition) which is regarded as magnetic dipole transition of J = ±1 (Figure 8b). 30,31 Scheme 1.…”

“…[26][27][28][29] Interestingly, excitation and emission spectra of RE 3? doped luminescent nanomaterials are independent of size of host matrix due to confined 4f-4f intraconfigurational transitions which are highly shielded by 5s and 5p orbitals. [30][31][32] Till now, the literature related to RE 3? doped Cu 3 P NCs is not reported to the best of our knowledge.…”