Synthesis Of Novel Broadband NIR Probes Based On Dual-mode Luminescence

This thesis focus on the design and synthesis of broadband near-infrared(NIR) probes based on dual-mode luminescence which includes quantum cutting(QC) and downshift(DS) process. Its contents following aspects:The Ca Ti O3:Bi3+,Yb3+ phosphor was synthesized by traditional high temperature solid-state method. The phosphor possessed a broad excitation band spanning from 300 to 480 nm, moreover, co-doping with Bi3+ made a significant enhancement in Yb3+ NIR integrated emission intensity by a factor of 10. According to the results, it evidenced the presence of energy transfer(ET) processes from Bi3+-Ti4+ metal-to-metal charge transfer state(BT-MMCTs) to Yb3+:2F5/2. The dependence of Yb3+ luminescent intensity on the excitation power was also measured and it demonstrates that the ET processes involve nonlinear cooperative energy transfer(CET) via two photons QC processes. This chapter laid the groundwork for the design and synthesis of a broadband near-infrared phosphor based on dual-mode luminescence.The broadband Ca Ti O3:Bi3+,Cr3+,Yb3+ NIR phosphor based on dual-mode luminescence was designed and synthesized. According to the PLE and PL spectra, the ET processes not only from BT-MMCTs to Yb3+ but from Cr3+ to Yb3+ were demonstrated in this phosphor, whose excitation band was ultra-broad and spanning from ultraviolet to whole visible region. And its excitation peak located at 466 nm. The dependence of Yb3+ luminescent intensities on the excitation power of 405 and 650 nm lasers was measured and it demonstrated that the ET processes from BT-MMCTs to Yb3+ were involved in nonlinear CET via two photons QC processes while from Cr3+ to Yb3+ were involved in linear DS via one photon processes. This chapter provided the thesis with a sound theoretical and experimental basis for the synthesis of broadband NIR nanoprobes based on dual-mode luminescence.The Ca Ti O3:Bi3+,Cr3+,Yb3+ NIR nanoprobes were synthesized by a sol-gel route. The results showed that calcined temperature played an important role in the structure, size, morphology and fluorescent intensities of nanoprobes. When the temperature raised from 800 to 1000 °C, it transformed near-spherical nanoparticles with 25-30 nm into polygon and agglomerate ones with ~200 nm size. In addition, the intensity of fluorescence also increased with the temperture.