Can NaYF4:Yb,Tm nanocrystals with multi-morphologies and various phases be synthesized by solvothermal process

The influencing factors of chelator, reaction times, and Yb 3+ /Tm 3+ -doped concentration on the formation of NaYF 4 :Yb,Tm crystals with various morphologies have been investigated and determined. It is found that NaYF 4 :Yb,Tm with various morphologies and different phases can be tuned. Compared with the addition of ethylene diamine tetra acetic acid, hexagonal nanoprism-like β-NaYF 4 :Yb,Tm with a mean length of ~ 1300 nm and diameter of ~ 100 nm is prepared in the presence of oleic acid, which preferentially orients along with the [0001] direction more quickly than others. Systematical research on the emission of Yb 3+ /Tm 3+ -doped NaYF 4 crystals with microrod, hexagonal microprism, and nanoplate has implied that these obtained crystals with unique optical properties are closely related to their morphologies, phases, and sizes. In addition, a possible growth mechanism of co-existence of α- and β-NaYF 4 phases is proposed. It can be expected to illustrate the formation mechanism for the upconversion crystals or other rare-earth upconversion materials and to import these highly luminescent microcrystals or nanocrystals to environmental remediation by full solar energy spectra.