Controlled Synthesis And Upconversion Luminescence Of Lanthanide Doped YPO₄Nanocrystals

Rare earth doped upconversion materials have drawn great attention because oftheir intrinsic properties such as narrow emission profiles, well photochemicalstability, low toxicity and large Stokes shift compared to organic dyes and quantumdots.In this paper, we have performed systematic investigations on YPO₄nanocrystals （NCs）. Hydrothermal preparation method and thermal decompositionpathway were used in synthesis process and Yb、Er、Ho、Tm were selected to becodoped in the matrix material YPO₄. X-ray powder diffraction （XRD）, Fieldemission scanning electron microscopy （FESEM）, Transmission electronmicroscopy （TEM）, fourier transform infrared spectroscopy （FT-IR） andphotoluminescence spectroscopy （PL） etc were used to study the crystal structure,size, morphology, forming mechanism and luminescence property of the as-preparedsamples. The main discussed results are as follows:1. OA was used as complexing agent firstly in the hydrothermal synthesisprocedure. Pure YPO₄: Yb³⁺/Er³⁺、YPO₄: Yb³⁺³⁺/Tm、YPO₄: Yb³⁺/Ho³⁺sampleswere obtained via controlling the ratio of PO3-4:Y³⁺and then the crystal phasetransition from tetragonal to hexagonal was able to be achieved via adjusting the pHvalue of the solution, hydrothermal time and temperature. Secondly, Na₃Cit wasused as complexing agent to synthesize regular YPO³⁺40.8H₂O: Yb/Er³⁺prismsuccessfully. It is found that the as-synthesized NCs prepared with Na₃Cit can beeasily dispersed in ethanol, while the other one can be easily dispersed in nonpolarcyclohexane solvent. Furthermore, up-conversion （UC） fluorescence under980nmNIR excitation of the samples were tested, whose results demonstrated thepromising application values in displays devices.2. OA was used as complexing agent and Oleylamine （OM） was used as solventin the thermal decomposition pathway. The nanowires and nanoparticles which havenarrow size distribution were obtained through adjusting the ratio of OA/OM. Inorder to enhance the luminescence intensity of the NCs, we successfully preparedthe core-shell structure of CaF³⁺2: Yb³⁺/Er@YPO₄, the luminescence intensity wasenhanced several times and it promoted the possibility in biomarker application.