A method is presented for the initiation of free-radical and free-radical-promoted cationic photopolymerizations by in-source lighting in the near-infrared (NIR) region using upconverting glass (UCG). This approach utilizes laser irradiation of UCG at 975 nm in the presence of fluorescein (FL) and pentamethyldiethylene triamine (PMDETA). FL excited by light emitted from the UCG undergoes electron-transfer reactions with PMDETA to form free radicals capable of initiating polymerization of methyl methacrylate. To execute the corresponding free-radical-promoted cationic polymerization of cyclohexene oxide, isobutyl vinyl ether, and N-vinyl carbazole, it was necessary to use FL, dimethyl aniline (DMA), and diphenyliodonium hexafluorophosphate as sensitizer, coinitiator, and oxidant, respectively. Iodonium ions promptly oxidize DMA radicals formed to the corresponding cations. Thus, cationic polymerization with efficiency comparable to the conventional irradiation source was achieved.

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The fabrication of size-dependent rare earth ion-doped materials for photonic devices has attracted interest in the search for color tunability and noncontact temperature sensing properties with high sensitivity. Sol–gel Pechini is an appropriate method compared to other methods to prepare Yb3+/Er3+:gadolinium gallium garnet (GGG) crystals at the nanoscale. This work presents a study of white-light emission and optical thermometry properties of Yb3+/Er3+:GGG nanocrystals based on the upconversion (UC) blue, green, and red emissions observed under 975 nm laser excitation. The color coordinates of the studied nanocrystals were affected by the crystalline size. Yb3+ (2 mol %)/Er3+(1 mol %):GGG nanocrystals have the highest maximum absolute sensitivities of 0.0028 K–1 at 378 K and 0.0041 K–1 at 561 K for 17 and 45 nm crystalline sizes, respectively. In light of the observations, Yb3+/Er3+:GGG may be a good candidate material for use in white light and optical temperature sensing.

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