A universal J–O calculation method for phosphors was proposed and used for NaYF₄:Er³⁺/Yb³⁺.

Temperature controllable photothermal therapy (PTT) requires a nanoplatform in which the optical temperature sensor and photothermal calorifier are integrated together. To establish such a nanoplatform, in this work we designed a NaYF₄:Er³⁺/Yb³⁺@NaYF₄:Tm³⁺/Yb³⁺ core-shell structure, and studied on its temperature sensing and photothermal conversion. The core-shell nanoparticles were prepared via a thermal decomposition method; furthermore, their crystal structure and microscopic morphology were characterized by means of XRD and SEM/TEM. The properties of temperature sensing and excitation power dependent fluorescence branching ratios were investigated. It was found that the temperature sensing could be achieved based on the fluorescence intensity ratio of green emissions from Er³⁺, but could not be realized by using other fluorescence intensity ratios. The photothermal conversion was demonstrated under 808 and 980 nm co-excitation, and the dependences of photothermal conversion on the excitation power and irradiation time of 808 nm laser were observed. Moreover, it was also found that the core-shell particles could effectively accelerate the evaporation of anhydrous ethanol, thus implying the photothermal conversion under single 980 nm laser excitation could also be achieved.

The non-specific interaction between the surface of gold nanorods (GNRs) and biomolecules is a significant problem in hyperthermia applications. In this work, a novel surface modification strategy was performed using zwitterionic oxidized glutathione (GSSG) to modify the GNRs through robust Au–S bond formation. The GSSG-GNRs were stable in aqueous solution over a broad range of pH and high ionic strength values. Importantly, the glutathione coating greatly reduced non-specific protein adsorption on GNRs due to zwitterions. In order to target tumor sites, folic acid (FA) and Rhodamine B (RBITC) dye were conjugated to GSSG modified GNRs through the reaction between the activated carboxyl group and the amino group. The targeting of RBITC-FA-GSSG-GNRs in human cervical carcinoma cells (HeLa cells) with high-level folate receptor expression was confirmed using confocal laser scanning microscopy (CLSM) to excite Rhodamine B dye at 488 nm. The targeting photothermal therapy efficacy was monitored in real time with the multi-channel function of a confocal laser scanning microscope coupled with an 808 nm laser. The results indicate that the FA-GSSG-GNR hybrids demonstrate efficient photothermal conversion and excellent targeting hyperthermia, and are therefore suitable for biomedical applications.