Crystal defect induced zero thermal quenching β-NaYF4: Eu3+, Sm3+ red-emitting phosphor

Red phosphors with brilliant performance are crucial for the application of white LEDs as their red-light component. However, the thermal quenching phenomenon is an inevitable obstacle in the practical application of various types of red-light phosphors. In this study, we report the preparation of a novel type of phosphor, NaYF4: 0.065Eu3+, 0.002Sm3+, possessing not only an energy transfer effect from Sm3+ to Eu3+ but also superior negative thermal quenching (NTQ) performance. The phosphor was synthesized via a one-step hydrothermal method, resulting in a prominent improvement in its luminous thermal stability supported by NTQ. The NTQ originated from the thermal stimulation excitement of the captured electrons in electronic traps, which is attributed to the non-equivalence between the different types of ions. The shape of the emission spectrum measured at high temperature was identical to that measured at room temperature, which not only showed the remarkable thermal stability of this novel type of phosphor but also the promising prospect of its practical application. This finding will contribute to improving the thermal stability of phosphor materials doped with lanthanide elements.

A crystal defect led zero thermal quenching β-NaYF4 : Eu3+,Dy3+ red emitting phosphor

Red-light phosphors with extraordinary and stable thermal luminous properties must urgently be explored under the circumstances that commercial phosphors are suffering from serious thermal quenching effects and a lack of red-light components. Synthesized by a one-step hydrothermal method, a new type of NaYF4 : 0.065Eu3+,0.003Dy3+ phosphor with notable thermal luminous stability is reported in this study. As well as energy transfer between Dy3+ and Eu3+, this novel red-light phosphor manifests zero thermal quenching (ZTQ) performance under an increasing temperature of measurement. The ZTQ property stems from the interior defects of the crystal produced by the non-equivalence replacement between distinct ions. Density Functional Theory (DFT) calculations were utilized to verify the formation energy of two kinds of defects that make a vital contribution to the ZTQ performance of the NaYF4 : 0.065Eu3+,0.003Dy3+ phosphor. This finding could make some contributions towards research into improving thermal luminous properties and stability.

Tuning Luminescence of Lanthanide-Doped Upconversion Nanoparticles through Simultaneous Binary Cation Exchange

Dual-mode luminescent nanomaterials have outstanding performance in biosensing and multistage anticounterfeiting. Herein, we report the tuning of optical attributes of lanthanide-doped nanoparticles (NPs) via simultaneous binary cation exchange. We show that cation exchange of NaYF₄:Yb/Er (18/2 mol %)@NaLnF₄ (Ln = Y and Gd) NPs with a combination of Ce³⁺ and Tb³⁺ enables the resultant nanoparticles to exhibit both upconversion and downshifting emissions upon excitation at 980 and 254 nm, respectively. We find that in addition to introducing downshifting emission attributes, the use of Tb³⁺ ions allows conservation of the integrity of the parent core@shell NPs by decreasing the dissociation tendency caused by Ce³⁺ ions during the cation exchange. The upconversion color output can be tuned from green to red and blue by changing lanthanide combinations in the core NPs. This work not only provides an effective strategy for the optical tuning of lanthanide-doped NPs but also builds a platform for probing the difference in the reactivity nature of lanthanides.

The morphology evolution, tunable down-conversion luminescence, and energy transfer of [CaY]F2 crystals doped with Li+/Ce3+/Tb3

Octahedral [CaY]F2 crystals with an average particle size of 1 μm were synthesized via a mild one-step hydrothermal route without employing any surfactants. Various morphologies, including cubes, truncated cubes, truncated octahedrons, and spheres, were achieved via manipulating the amount of EDTA used, and a possible growth mechanism was proposed based on the surface energies of different crystal planes and the influence of the surfactant. XRD, SEM, EDS, TEM, HRTEM, and PL analysis were used to characterize the products. The effects of the morphologies and Li+ doping concentrations on the luminescence intensities of the [CaY]F2:Ce3+/Tb3+ phosphors were explored, and the strongest luminescence intensity is obtained when the sample is cubic with (100) crystal faces and the doping concentration of Li+ is 0.25 mol%. Additionally, multicolor emission (blue → aquamarine blue → green) was obtained from [CaY]F2:Ce3+/Tb3+ phosphors via adjusting the doping concentration of Tb3+, which resulted from the Ce3+ → Tb3+ energy transfer behavior; the energy transfer here happened through a dipole-dipole mechanism. This work may result in the as-synthesized phosphors having great application potential in many optoelectronic device fields, such as in displays and multicolor lighting.

Morphology control, spectrum modification and extended optical applications of rare earth ion doped phosphors

This review summarizes the morphology control strategy, phase transfer theory, spectrum modulation, and extended optical applications of RE³⁺-doped phosphors.

Morphological evolution of upconversion nanoparticles and their biomedical signal generation

Advancements in the fabrication of upconversion nanoparticles (UCNPs) for synthetic control can enable a broad range of applications in biomedical systems. Herein, we experimentally verified the role of the hydrothermal reaction (HR) time in the synthesis of NaYF₄:20%Yb³⁺/3%Er³⁺ UCNPs on their morphological evolution and phase transformation at different temperatures. Characterizations of the as-prepared UCNPs were conducted using X-ray diffraction (XRD), electron microscopy and spectroscopy, and thermogravimetric and upconversion (UC) luminescence analysis. We demonstrated that determining the optimal HR time, also referred to here as the threshold time, can produce particles with good homogeneity, hexagonal phase, and UC luminescence efficiency. Subsequently, the polymer coated UCNPs maintained their original particle size distribution and luminescence properties, and showed improved dispersibility in a variety of solvents, cellular nontoxicity, in vitro bioimaging, and biocompatibility as compared to the bare UCNP. Besides this, polyacrylic acid conjugated UCNPs (UCNP@PAA) also revealed the strong anticancer effect by conjugating with doxorubicin (DOX) as compared to the free DOX. Based on these findings, we suggest that these particles will be useful in drug-delivery systems and as in vivo bioimaging agents synchronously.

Facile hydrothermal synthesis of Tb2(MoO4)3:Eu3+ phosphors: controllable microstructures, tunable emission colors, and the energy transfer mechanism

Microsphere-like Tb₂(MoO₄)₃ structures have been successfully synthesized by a facile hydrothermal method with the subsequent calcination treatment.