Tuning the Energy Transfer Efficiency between Ce³⁺ and Ln³⁺ Ions (Ln=Tm, Sm, Tb, Dy) by Controlling the Crystal Phase of NaYF₄ Nanocrystals

Abstract

NaYF is a superior host matrix to study the luminescence properties of lanthanide (Ln ) ions. Ln ions in hexagonal-phase NaYF (β-phase) nanocrystals (NCs) exhibit strong luminescence via an upconversion process compared to cubic NaYF (α-phase) NCs. However, in Ce /Ln -doped NaYF NCs (Ln=Tm, Tb, Sm, Dy) the α-phase NaYF NCs shows strong luminescence compared to their counterpart β-phase NCs despite the latter being much larger in size. This is attributed to comparatively large overlap between Ce ions emission band with excited energy levels of those Ln ions in α-phase compared to β-phase NCs. This difference is attributed to different crystal-field splitting of Ce ions 4f-5d band in different crystal environments of the α-phase (cubic crystal field environment) and β-phase (trigonal prismatic with equatorials crystal field environment) NaYF NCs with respect to their barycenter. The enhanced luminescence from α-phase NaYF NCs is advantageous as they are prepared at a relatively lower temperature and shorter reaction times compared to β-NaYF NCs.

Ce3+‐Sensitized Tm3+/Mn2+‐Doped NaYF4 Colloidal Nanocrystals: Intense Cool White Light from a Phosphor‐Coated UV LED

“…NaYF 4 exhibits in two polymorphic forms; cubic (α) and hexagonal (β). Our idea is to consider cubic phase NaYF 4 as a host matrix as recently we observed that Ce 3+ → Ln 3+ energy transfer is more efficient in cubic phase NaYF 4 compared to hexagonal NCs …”

“…Ln 3 + energy transfer is more efficient in cubic phase NaYF 4 compared to hexagonal NCs. [20] In this work, we report the synthesis of citric acid (CA)capped Ce 3 + /Tm 3 + /Mn 2 + doped NaYF 4 nanocrystals (NCs) using am icrowave method. The strong white light emission is the result of combining the blue (Tm 3 + )a nd green-yellow (Mn 2 + )e missions via energy transfer through Ce 3 + ion sensitization (280 nm excitation).…”

Ligand‐Sensitised LaF3:Eu3+ and SrF2:Eu3+ Nanoparticles and in Vitro Haemocompatiblity Studies

“…However, the Eu 3 + ions cannot be sensitised directly by Ce 3 + ions. [7][8][9] Recently, a good strategy for sensitising Ln 3 + ions in Ln 3 + -doped nanoparticles has been developed. [10][11][12][13][14] The Ln-doped NPs surface functionalised with aromatic organic ligands, these ligand molecules act as a surfactant to control the growth of the NPs and to make colloidal dispersion of the NPs in aqueous and organic media.…”

“…The common activator ions for the downshifting process are Eu 3+ , Tb 3+ , while Er 3+ , Tm 3+ ions are for up‐conversion. However, the Eu 3+ ions cannot be sensitised directly by Ce 3+ ions [7–9] …”

Simultaneous 980 and 800 nm Orthogonal Upconversion and Ligand-Sensitized Downshifting of Triply Excited and Multicolor-Emitted Core–Multishell Nanocrystals for High-Level Anticounterfeiting Applications

“…Lanthanides possess unique optical characteristics due to their intra 4f–4f transitions, resulting in color specificity and sharp emission bands. − Ln-based NCs demonstrate both Stokes (downshifting, DS) and anti-Stokes (upconversion, UC) emission processes, depending on the sensitizer and activator ions . Ln-based NCs can be excited under UV light (254 or 350 nm) or NIR light (800, 980, and 1550 nm). − For example, in the UC process, Er (green and red), Tm (blue), and Ho (green and red) ions serve as activators, with Yb and Nd acting as sensitizers for excitations of wavelengths 980 and 800 nm, respectively .…”