Facile synthesis and emission enhancement in NaLuF4 upconversion nano/micro-crystals via Y3+ doping

Hao Lin,Shenghong Yang,Zhiren Qiu,Yueli Zhang,Anming Li,Lu Yao,Dekang Xu

doi:10.1038/s41598-017-14228-9

Abstract

A series of Y3+-absent/doped NaLuF4:Yb3+, Tm3+ nano/micro-crystals were prepared via a hydrothermal process with the assistance of citric acid. Cubic nanospheres, hexagonal microdisks, and hexagonal microprisms can be achieved by simply adjusting the reaction temperature. The effect of Y3+ doping on the morphology and upconversion (UC) emission of the as-prepared samples were systematically investigated. Compared to their Y3+-free counterpart, the integrated spectral intensities in the range of 445–495 nm from α-, β-, and α/β-mixed NaLuF4:Yb3+, Tm3+ crystals with 40 mol% Y3+ doping are increased by 9.7, 4.4, and 24.3 times, respectively; red UC luminescence intensities in the range of 630–725 nm are enhanced by 4.6, 2.4, and 24.9 times, respectively. It is proposed that the increased UC emission intensity is mainly ascribed to the deformation of crystal lattice, due to the electron cloud distortion in host lattice after Y3+ doping. This paper provides a facile route to achieve nano/micro-structures with intense UC luminescence, which may have potential applications in optoelectronic devices.

Highlights

UC emission intensity is mainly ascribed to the deformation of crystal lattice, due to the electron cloud distortion in host lattice after Y3+ doping
It can be concluded that higher reaction temperature favors the formation of NaLuF4 crystals with hexagonal phase, which is ascribed to the fact that higher temperature favors the nucleation and the crystal growth[25]
Cubic nanospheres, hexagonal microdisks, and hexagonal microprisms can be achieved by adjusting the reaction temperature

Summary

Introduction

UC emission intensity is mainly ascribed to the deformation of crystal lattice, due to the electron cloud distortion in host lattice after Y3+ doping. Zhao et al reported the enhanced red UC emission in Mn2+ doped NaYF4: Yb/Er nanoparticles, due to the efficient energy transfer between Er3+ and Mn2+ 11. Zhao’s group reported Li+ doped GdF3:Yb3+, Er3+ nanocrystals with the enhanced red UC luminescence, which was caused by the decrease of local crystal field symmetry around activators after Li+ doping[14]. Yin et al reported Mo3+ doped NaYF4: Yb/Er nanocrystals with 6 and 8 times enhancement of green and red UC emissions, due to the lattice distortion after Mo3+ doping[16]. The ionic radius of Y3+ (0.89 Å) is larger than that of Lu3+ (0.85 Å), Y3+ doping may cause the expansion of NaLuF4 host lattice, leading to the distortion of local symmetry around activators. The proposed mechanisms of UC emission enhancement and shape evolution through introducing Y3+ are presented

Methods

Results

Conclusion