The Effect of Hydrothermal Treatment on the Morphologies and Optical Properties of Upconversion NaYF4:Ln3+ Crystals

Abstract

This work deals with the synthesis and characterization of upconversion NaYF 4 :Ln 3+ crystals. Co-precipitation and hydrothermal methods were used to synthesize NaYF 4 :Ln 3+ crystals. The experimental procedures were modified to obtain crystals in the cubic (α) phase, hexagonal (β) phase or a mixture between cubic and hexagonal (α/β) phases. Reaction temperature was maintained at 200 °C and the time of hydrothermal treatments were maintained at 24 and 48 h. The average diameter of the crystals ranged from 25 nm to 6.4 µm, depending on the chosen synthetic route. These materials can be applied in areas such as photodynamic therapy and bioimaging.

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

“…23 Possessing the abundant merits of fluorides, NaYF 4 is an outstanding matrix and exhibits high compatibility with lanthanides, for instance Eu, Yb, Er, Tm, Ho and Nd. 22,24 Furthermore, flexible routes can be employed for the synthesis of NaYF 4 -based phosphors, such as thermal decomposition, hydrothermal method, electrospinning process, and microwave synthesis. 25–28 Among them, the hydrothermal method is the safest the most cost-effective for the synthesis of NaYF 4 -based phosphors due to its convenient operation process and moderate synthesis environment, exhibiting high safety.…”

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

“…Unlike nitride-based phosphors, there are distinct synthesis strategies to obtain NaYF 4 phosphors with high chemical stability and luminous properties, such as electrospinning, 28 thermal decomposition, 29 co-precipitation, 30 and the hydrothermal method. 31,32 In these mentioned synthesis methods, the hydrothermal method is the most cost-effective synthesis compared with thermal decomposition and electrospinning. Moreover, the hydrothermal method has better safety and operational processes.…”