Morphology evolution and pure red upconversion mechanism of β-NaLuF4 crystals

Abstract

A series of β-NaLuF4 crystals were synthesized via a hydrothermal method. Hexagonal phase microdisks, microprisms, and microtubes were achieved by simply changing the amount of citric acid in the initial reaction solution. Pure red upconversion (UC) luminescence can be observed in β-NaLuF4:Yb3+, Tm3+, Er3+ and Li+ doped β-NaLuF4:20% Yb3+, 1% Tm3+, 20% Er3+. Based on the rate equations, we report the theoretical model about the pure red UC mechanism in Yb3+/Tm3+/Er3+ doped system. It is proposed that the pure red UC luminescence is mainly ascribed to the energy transfer UC from Tm3+:3F4 → 3H6 to Er3+:4I11/2 → 4F9/2 and the cross-relaxation (CR) effect [Er3+:4S3/2 + 4I15/2 → 4I9/2 + 4I13/2] rather than the long-accepted mechanism [CR process among Er3+:4F7/2 + 4I11/2 → 4F9/2 + 4F9/2]. In addition, compared to the Li+-free counterpart, the pure red UC luminescence in β-NaLuF4:20% Yb3+, 1% Tm3+, 20% Er3+ with 15 mol% Li+ doping is enhanced by 13.7 times. This study provides a general and effective approach to obtain intense pure red UC luminescence, which can be applied to other synthetic strategies.

Synthesis of Multicolor Core/Shell NaLuF4:Yb3+/Ln3+@CaF2 Upconversion Nanocrystals

“…NaLuF 4 -based UCNCs have been demonstrated to exhibit bright upconversion luminescence (UCL) [17,18,19,20,21,22,23,24] and show efficient five- and four-photon ultraviolet emissions under continuous wave excitation at 980 nm [25,26,27]. Despite recent success in synthesizing NaLuF 4 nanoplates or nanorods with size over ~30 nm using thermal decomposition method [28,29,30,31] or hydrothermal method [32,33,34,35,36,37,38], the ability to prepare uniform single crystal phase sub-10 nm NaLuF 4 UCNCs remains elusive. Moreover, doping of a high concentration of inert Gd 3+ ions (≥20%) was typically required to prepare small-sized monodisperse NaLuF 4 UCNCs with single crystal phase previously [17,39], thus delivering traits actually from an entity of Lu-Gd alloyed host.…”

Improving Optical Temperature Sensing Performance of Er3+ Doped Y2O3 Microtubes via Co-doping and Controlling Excitation Power

“…If the emission intensity ratios from the 2 H 11/2 and 4 S 3/2 is adjusted, the temperature sensitivity will change greatly. As reported that the energy gaps between 3 F 4 and 3 H 6 of Tm 3+ ion, as well as between 5 I 7 and 5 I 8 of Ho 3+ ion, were equal to the energy gap between 2 H 11/2 and 4 F 9/2 of Er 3+ ion 19 . Thus, the population of 2 H 11/2 and 4 S 3/2 levels of Er 3+ can be adjusted through the cross relaxation energy transfer between Er 3+ and Tm 3+ (or Ho 3+ ).…”

“…At present, trivalent rare earth ions, such as Er 3+ , Ho 3+ , Tm 3+ , Eu 3+ , and Pr 3+ , have been used as activators to study optical temperature sensing behaviors 13 – 18 . Among these ions, Er 3+ is preferred for temperature sensing due to the large energy gap (about 800 cm −1 ) and small overlap of the two emission peaks from 2 H 11/2 and 4 S 3/2 levels 19 – 22 . So the optical thermometry based on up-conversion emission of Er 3+ doped phosphors has been explored in different hosts by using infrared excitation sources 12 – 18 .…”

Spectral management and energy‐transfer mechanism of Eu3+‐doped β‐NaGdF4:Yb3+,Er3+ microcrystals

“…Both the population density and accuracy of the ET1 and ET2 models can be confirmed by rate equations, which have been successfully used to interpret the ET process between Yb 3+ and Er 3+ in several host matrices 34,36,37 . The corresponding rate equations of ET1 and ET2 are shown as Table 1.…”