The crystal structure and upconversion properties of Yb³⁺, Er³⁺/Ho³⁺ codoped BaLiF₃ microcrystals with different morphologies

Abstract

A series of x mol% Yb(3+), 1 mol% Ho(3+)/1 mol% Er(3+) (0 ≤ x ≤ 25) codoped BaLiF3 microcrystals with different cubic morphologies and sizes (1.52 μm-3.83 μm) were synthesized by a facile surfactant-assisted hydrothermal-microemulsion approach for the first time. The crystalline structure of BaLiF3 was established via the Rietveld refinement result of the powder X-ray diffraction (XRD) data. In addition, the growth process of cubic BaLiF3 crystals and the influence of different synthesis conditions on the morphology were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, in this paper we first investigated the upconversion luminescence (UCL) properties of new Er(3+)/Ho(3+), Yb(3+)-codoped BaLiF3 microcrystals under 980 nm excitation. The characteristic emission of Er(3+) and Ho(3+) was obtained, respectively. The blue emission in BaLiF3:Yb(3+), Ho(3+) which was comparatively more difficult to discover was also observed and explained by the energy level diagram. It is worthwhile to point out that BaLiF3:Yb(3+), Er(3+) practically showed pure red upconversion (UC) emission under excitation at 980 nm and the reasons behind this behavior are presented and discussed.

Yb3+ and Er3+ Codoped BaLiF3 Nanocrystals for X-ray Dosimetry and Imaging by Upconversion Luminescence

“…To achieve a near 100% purity of BaLiF 3 :Yb 3+ , Er 3+ phase, samples of BaLiF 3 :1% Er 3+ with different Yb 3+ concentrations were prepared by ball milling for an extended time of 4 h. In Figure a, the upconversion emission spectra of as-prepared BaLiF 3 : x % Yb 3+ , 1% Er 3+ ( x = 1, 5, and 10) nanocrystals are shown. As-prepared samples with different Yb 3+ concentrations show the same upconversion bands located at 521, 540, and 650 nm, and the sample doped with the highest Yb 3+ concentration (BaLiF 3 :10% Yb 3+ , 1% Er 3+ ) exhibits the maximum emission intensity (Figure a) in agreement with the literature . The enhancement of the upconversion intensity is due to the reduced average distance between Er 3+ and Yb 3+ ions with increasing Yb concentration.…”

“…From data presented in Figure b, n values of 1.56 ± 0.02, 1.68 ± 0.02, and 1.68 ± 0.02 were determined for the three upconversion luminescence bands 2 H 11/2 → 4 I 15/2 (521 nm), 4 S 3/2 → 4 I 15/2 (540 nm), and 4 F 9/2 → 4 I 15/2 (650 nm), respectively. These values indicate that the upconversion mechanism in nanocrystalline BaLiF 3 :Yb 3+ , Er 3+ is based on a two-photon process, a result that is in accord with the literature . The energy-transfer (ET) based mechanism is illustrated in Figure c.…”

“…BaLiF 3 can be readily prepared from equimolar amounts of BaF 2 and LiF by mechanochemical methods including high-energy ball milling. , Recently, BaLiF 3 has been investigated as a potential upconversion host material. For example, microcrystalline BaLiF 3 doped with Yb 3+ , Er 3+ /Ho 3+ (crystal size ∼2–4 μm) was prepared by a surfactant-assisted hydrothermal-microemulsion method . In this article, we report the successful preparation of nanocrystalline BaLiF 3 :Yb 3+ , Er 3+ that shows infrared-to-visible upconversion luminescence.…”

Eu-Doped BaF2 Nanoparticles for Bioimaging Applications

“…Furthermore, judicious selection of host materials is also a prerequisite for doping of RE 3+ ions. Nowadays, various inorganic compounds such as oxides, phosphates, vanadates, and fluorides have been explored as host materials. − Among them, binary and ternary alkali/alkaline or RE based fluoride nanoparticles have drawn significant attention due to the fulfillment of desired prerequisites such as low phonon energy, high refractive index, tunable crystal phase, low cost of production, and large band gap. − …”

Preparation and Structure of New Oxyfluoride Glass‐Ceramics Containing BaLiF3 Nanocrystal

“…As shown in Fig. 1, it cannot only offer the Ba 2+ sites of O h symmetry for REIs, 14,15 but also provide the octahedral sites of Li + for the TMIs, for example, Ni 2+ and Co 2+ , to give rise to broadband emissions. 16,17 Thus, this work attempts to obtain the BaLiF 3 nanocrystallized oxyfluoride GCs with an elaborate glass design, and their microstructural features are also present and discussed in detail.…”