Sai Xu

NaYF_4:Sm^3+/Yb^3+@NaYF_4:Er^3+/Yb^3+ core-shell structured nanocalorifier with optical temperature probe

A core-shell structure with a NaYF4:Sm3+/Yb3+ core for photothermal conversion nanocalorifier and a NaYF4:Er3+/Yb3+ shell as temperature probe for potential applications in photothermal therapy (PTT) were synthesized by a thermal decomposition technique of rare-earth oleate complexes. The optical temperature reading-out property for the NaYF4:Sm3+/Yb3+@NaYF4:Er3+/Yb3+ core-shell structure was systematically investigated and it was found that in comparison with pure NaYF4:Er3+/Yb3+ particles, the temperature sensing performance of the NaYF4:Er3+/Yb3+ shell did not become worse due to the presence of NaYF4:Sm3+/Yb3+ core. Furthermore, the photothermal conversion behavior for core-shell nanoparticles was successfully examined by dint of temperature sensing of the NaYF4:Er3+/Yb3+ shell, and it was found that an excitation-power-density-dependent temperature increase of up to several tens degrees can be achieved. All the experimental results suggested that the core-shell structure may be an excellent nanocalorifier candidate for advanced temperature-controllable PTT.

Concentration-dependent spectroscopic properties and temperature sensing of YNbO4:Er3+ phosphors

A series of YNbO4:Er3+ phosphors with various Er3+ concentrations was synthesized via a traditional high temperature, solid-state reaction method. XRD Rietveld refinements based on the XRD data were carried out to study the phase purity and crystal structure of the as-prepared samples. The results revealed that single monoclinic phase YNbO4 phosphors were obtained. The influence of the Er3+ concentration on the spectroscopic properties and temperature sensing in YNbO4:Er3+ phosphors were systematically studied. Different quenching concentrations were found in down-conversion and up-conversion luminescence processes. From lasers working current dependent up-conversion luminescence spectra, it was confirmed that two and three photon processes were responsible for both the green and the red up-conversion emissions, respectively, excited by 980 and 1550 nm lasers, which have no apparent dependence on Er3+ ion concentration. However, the Er3+ concentration had significant influences on the temperature sensing sensitivity of Er3+ ions, and the results showed that YNbO4 phosphors doped with low concentrations of Er3+ ions had high temperature sensing sensitivity and could be applied in temperature detection applications, particularly in high temperature environments.

Dually functioned core-shell NaYF 4 :Er 3+ /Yb 3+ @NaYF 4 :Tm 3+ /Yb 3+ nanoparticles as nano-calorifiers and nano-thermometers for advanced photothermal therapy

To realize photothermal therapy (PTT) of cancer/tumor both the photothermal conversion and temperature detection are required. Usually, the temperature detection in PTT needs complicated instruments, and the therapy process is out of temperature control in the present investigations. In this work, we attempt to develop a novel material for achieving both the photothermal conversion and temperature sensing and control at the same time. To this end, a core-shell structure with NaYF4:Er3+/Yb3+ core for temperature detection and NaYF4:Tm3+/Yb3+ shell for photothermal conversion was designed and prepared. The crystal structure and morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Furthermore, the temperature sensing properties for the NaYF4:Er3+/Yb3+ and core-shell NaYF4:Er3+/Yb3+@NaYF4:Tm3+/Yb3+ nanoparticles were studied. It was found that the temperature sensing performance of the core-shell nanoparticles did not become worse due to coating of NaYF4:Tm3+/Yb3+ shell. The photothermal conversion behaviors were examined in cyclohexane solution based on the temperature response, the NaYF4:Er3+/Yb3+@NaYF4:Tm3+/Yb3+ core-shell nanoparticles exhibited more effective photothermal conversion than that of NaYF4:Er3+/Yb3+ nanoparticles, and a net temperature increment of about 7 °C was achieved by using the core-shell nanoparticles.

Up-conversion luminescence, temperature sensing properties and laser-induced heating effect of Er3+/Yb3+ co-doped YNbO4 phosphors under 1550 nm excitation

YNbO4 phosphors with various Er3+ and Yb3+ concentrations were synthesized via a traditional high-temperature solid-state reaction method. Their crystal structure was investigated by means of X-ray diffraction (XRD) and Rietveld refinements, and it was confirmed that the obtained samples exist in monoclinic phase. The Er3+ and Yb3+ concentration-dependent up-conversion (UC) luminescence was studied under 1550 nm excitation. By inspecting the dependence of UC intensity on the laser working current, it was found that four-photon and three-photon population processes were co-existent for generating the green UC emissions in the samples with higher Yb3+ concentrations. In addition, it was observed that the temperature sensing properties of YNbO4: Er3+/Yb3+ phosphors were sensitive to both Er3+ and Yb3+ doping concentrations. Furthermore, based on the obtained temperature response of the UC luminescence phosphors, 1550 nm laser-irradiation-induced thermal effect was studied, and it was discovered that the sample temperature was very sensitive to the doping concentrations of Er3+ and Yb3+ and the excitation power.

Experimental optimum design and luminescence properties of NaY(Gd)(MoO4)2:Er3+ phosphors*

Three-factor orthogonal design (OD) of Er3+/Gd3+/T (calcination temperature) is used to optimize the luminescent intensity of NaY(Gd)(MoO4)2:Er3+ phosphor. Firstly, the uniform design (UD) is introduced to explore the doping concentration range of Er3+/Gd3+. Then OD and range analysis are performed based on the results of UD to obtain the primary and secondary sequence and the best combination of Er3+, Gd3+, and T within the experimental range. The optimum sample is prepared by the high temperature solid state method. Photoluminescence excitation and emission spectra of the optimum sample are detected. The intense green emissions (530 nm and 550 nm) are observed which originate from Er3+ 2H11/2→ 4I15/2 and 4S3/2→4I15/2, respectively. Thermal effect is investigated in the optimum NaY(Gd3+)(MoO4)2:Er3+ phosphors, and the green emission intensity decreases as temperature increases.