Controlled hydrothermal growth and tunable luminescence properties of β-NaYF4:Yb3+/Er3+ microcrystals

Using a facile hydrothermal method , hexagonal β-NaYF 4 :Yb 3+ 20   mol%, Er 3+ 1   mol% crystals with predictable size and morphology were synthesized and the upconversion (UC) luminescence properties were investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectra were used to characterize the samples. The results indicated that the size and morphology of the crystals can be precisely controlled by tuning the pH values of the initial reaction solution and the molar ratio of NaNO 3 to RE 3+ (RE   =   Y   +   Yb   +   Er), and the mechanism was proposed. The UC luminescence properties of β-NaYF 4 :Yb 3+ /Er 3+ crystals were found to strongly depend on the crystal morphologies and sizes. The peak area ratio of green to red (R/G) increased from 0.29 to 1.03 with pH values increasing from 3 to 10, and increased from 1.03 to 1.26 with the increase of molar ratio of NaNO 3 to RE 3+ from 0 to 90. The emission colors were tuned from pure green to orange yellow. This study provides a facile way to synthesize β-NaYF 4 :Yb 3+ /Er 3+ crystals with predictable morphology and size, and tunable luminescence properties, which can be applicable for other rare earth fluoride compounds.