Tuning of structure and enhancement of upconversion luminescence in NaLuF₄:Yb³⁺,Ho³⁺ crystals

Abstract

A series of NaLuF4:Yb(3+),Ho(3+) nano/micro-crystals with different crystal structures were synthesized via a hydrothermal method using citric acid as a chelating agent. The influences of NaF content, Li(+) doping, reaction temperature and reaction time on the crystal structure and shape of the as-synthesized NaLuF4 crystals were systematically investigated. To the best of our knowledge, it is the first time to report Li(+) doped α-NaLuF4:Yb(3+),Ho(3+) nanocrystals and the phase transformation by introducing Li(+) in NaLuF4 crystals. As for Li(+) doped α-NaLuF4, UC luminescence intensities of green emission (538 nm) and red emission (644 nm) in α-NaLuF4:Yb(3+),Ho(3+) nanocrystals with 20 mol% Li(+) doping are enhanced by 20 and 3.5 times compared to their Li(+)-free counterpart. As for Li(+) doped α/β-mixed NaLuF4, with the increase of Li(+) content, the phase transforms from the α/β-mixed phase to hexagonal then to cubic. UC emissions of 538 nm and 644 nm in NaLuF4:Yb(3+),Ho(3+) crystals doped with 5 mol% Li(+) are enhanced by 26.5 and 23 times, respectively. Besides, it is found that with the higher temperature and prolonged time, the morphology of NaLuF4 changes from nanoparticles to microtubes, resulting in the dramatic increase of UC emission intensity. The effects of Li(+) doping, reaction temperature and reaction time on the enhancement of UC emission intensity are discussed in detail. This study provides an effective and facile approach to obtain nano/micro-crystals with controllable structures and excellent optical properties.

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.…”

BaTiF6:Mn4+bifunctional microstructures with photoluminescence and photocatalysis: hydrothermal synthesis and controlled morphology

“…4 shows the SEM images of the hydrothermal products synthesized at 120°C for different reaction times. According to the morphology evolution with increasing reaction temperature, it is concluded that the formation rate of nucleation and the crystal growth rate are expedited with raising the reaction temperature, which will result in the formation of products with a large scale 44 . When the reaction time is extended to 5 h, the bundle-like microstructures continue to grow into the fantails, which are composed of many thin and small microrods.…”

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

“…All samples were prepared based on our previously reported procedures 22–24 . As for the synthesis of Y 3+ -absent α-NaLuF 4 :20%Yb 3+ , 1%Tm 3+ nanocrystals, 3 mmol of citric acid (2 M, 1.5 mL), 5 mmol of NaOH (4 M, 1.25 mL) and 10 mL of deionized water were mixed and stirred for 10 min.…”