Manipulating energy transfer in lanthanide-doped single nanoparticles for highly enhanced upconverting luminescence

We demonstrate a multilayer-structured design strategy to manipulate the deleterious CR-ETs in lanthanide-doped UCNPs for highly enhanced upconverting luminescence.


S3
General procedure for the preparation of nanorod-tagged polystyrene beads. In a typical procedure, 100 μL of polystyrene beads (diameter 9-9.9 μm, 5% w/v) were first dispersed in the mixture of 1 mL 1-butanol and 1 mL dichloromethane, and then 500 μL dichloromethane solution containing 20 mg/mL multilayer-structured KSc 2 F 7 nanorods was added and kept shaking gently at room temperature for 3 h. Thereafter, 4 mL of ethanol was added into the above mixture to stop the swelling of polystyrene beads, and the resulting nanorod-tagged polystyrene beads were collected by centrifugation at 6000 rpm for 5 min, washed with ethanol 3 times and redispersed in ethanol.
Preparation of water-soluble KSc 2 F 7 nanorods. To render the hydrophobic nanorods hydrophilic, we removed the original OA ligands from their surface by acid treatment as previously reported. 2 In a typical process, 20 mg of the assynthesized OA-capped KSc 2 F 7 nanorods were dispersed in 30 mL of acidic ethanol solution (pH 1) and ultrasonicated for 30 min to remove the surface ligands. After the reaction, the nanorods were collected by centrifugation at 12000 rpm for 10 min, and further purified by adding an acidic ethanol solution (pH 4). The resulting water-soluble KSc 2 F 7 nanorods were washed with ethanol and distilled water for several times, and then re-dispersed in distilled water for the following use.
Inkjet printing or handwritting of multilayer-structured KSc 2 F 7 nanorods on banknote. A common ink cartridge of the commercial inkjet printer (HP Deskjet 1112) was washed with ethanol until the ink was completely cleared away.
After the vacant cartridge was dried, 1 mL of water solution of water-soluble multilayer-structured KSc 2 F 7 nanorods (30 mg/mL) was injected into the HP 803 cartridge. Subsequently, the printing was carried out by an inkjet printer connected with a computer, and thus the nanorods were patterned on a piece of A4 paper. The two-dimensional (2D) code and multicolored sketch were printed by using the inkjet printer, while the Arabic numbers of "123456" were handwritten on the A4 paper. The colorful UC luminescence pictures were taken by a Canon 70D camera upon irradiation using a 980-nm diode laser at a power density of ~200 W cm -2 , where a short pass filter of 750 nm was placed in the front of the camera to filter the 980-nm excitation light.
Theoretical Analysis for UC Luminescence Lifetime of Ln 3+ Ion. It is well known that the observed lifetime () for a particular excited state (luminescent level) of Ln 3+ ion is determined by the sum of the inverse of the radiative and nonradiative rates, which can be expressed as: , where W R and W NR are the total radiative and nonradiative relaxation rates from the excited state of interest, respectively. 3 The total radiative relaxation rate is mainly evaluated via Einstein spontaneous emission coefficients of Ln 3+ ions, which can be regarded as a constant in a given host material. By contrast, the nonradiative relaxation rate is primarily determined by the magnitude of the energy gap between the luminescent and its next lowest-lying states of Ln 3+ ions, which thereby can be significantly affected by   Figure S19b). This feature makes these multilayer-structured we synthesized via a modified stepwise oriented epitaxial growth method, enhanced UC luminescence coupled with prolonged UC lifetimes were also detected in Tm@Er@pure NaYF 4 nanorods. These results clearly demonstrate that the design strategy we adopted for inhibiting CR-ETs of multiple Ln 3+ ions can be readily generalized for the most promising UC luminescent system of -NaYF 4 , thus revealing the universality of the multilayer-structured strategy we specifically designed for highly enhanced UC luminescence.