Flux Growth of Highly Crystalline NaYF₄:Ln (Ln = Yb, Er, Tm) Crystals with Upconversion Fluorescence

Abstract

Highly crystalline, NaYF4 and NaYF4:Ln (Ln = Yb, Er, Tm) crystals with upconversion fluorescence were successfully grown by the cooling of the solo NaF flux at a holding temperature of 1100 °C and cooling rate of 5 °C·h−1. The basic forms of NaYF4 and NaYF4:Ln crystals were a sphere. The crystal system, form, and size were affected by cooling rate. The red, green, and blue upconversion fluorescence of NaYF4:Ln crystals were clearly observed under 980 nm laser irradiation by a two- or three-photon upconversion process. The upconversion fluorescence of NaYF4:Ln crystals was successfully controlled by changing the cooling rate and type of dopant. Furthermore, the NaYF4:Yb,Er crystals were successfully grown using a mixed NaF-KF flux cooling method at a relatively low temperature of 800 °C.

Flux growth of honeycomb-like β-NaYF4:Yb3+, Er3+/Tm3+ crystals with multicolor upconversion luminescence

“…3. These emission spectra are similar to those for Yb 3 þ ,Er 3 þ or Yb 3 þ ,Tm 3 þ co-doped hexagonal NaYF 4 nanocrystals, microtubes microrods and microprism reported previously [15][16][17][20][21][22]. In Fig.…”

“…Up to now, several techniques have been employed for synthesis of b-NaYF 4 , such as solid reaction [8], coprecipitation [12], hydrothermal [13,14], flux cooling methods [15][16][17]. Comparing with other methods, the flux cooling method is a facile mass production method with inexpensive equipment, low environment loads and high crystalline.…”

“…Comparing with other methods, the flux cooling method is a facile mass production method with inexpensive equipment, low environment loads and high crystalline. Recently, b-NaYF 4 nanospheres [15], microtubes and microrods [17] were successfully prepared by flux cooling method using NaF-KF or NaNO 3 -KNO 3 flux. Here, we employed this mixed NaCl-KCl flux cooling method for synthesis of honeycomb-like b-NaYF 4 with multicolor UC luminescence.…”

Up-conversion luminescent properties and optical thermometry of LaMgAl11O19: Yb3+/Er3+ phosphors

“…The FIR of two emissions from 2 H 11/2 / 4 S 3/2 -4 I 15/2 transitions increases with the rise in sample temperature. The reason is that the state of 2 H 11/2 could be populated effectively from 4 S 3/2 through a thermalization process, which will result in the relative variation of intensity between the two thermally coupled levels to ensure a quasi-thermal equilibrium according to the Boltzmann distribution [5]. With the thermalization of population at the 2 H 11/2 and 4 S 3/2 levels and ignoring the effects of selfabsorption of the fluorescence, the ratio of green UC emission intensity at 525 and 545 nm can be expressed by the following equation [35,36].…”

“…For the RE ions with coupled levels, Er 3 þ has been investigated extensively due to its green UC emissions originating from two thermally coupled levels 2 H 11/2 and 4 S 3/2 . In order to improve its efficiencies and absorptions at 980 nm, Yb 3 þ is often used as an efficient sensitizer in UC system since it possesses only one excited f-electron level that allows a strong and broad absorption band around 980 nm [5].…”