Effect of ytterbium amount on LaNbO4:Tm3+,Yb3+ nanoparticles for bio-labelling applications

Abstract Purpose This work investigates how Yb3+ concentration affects the luminescent properties of LaNbO4 nanoparticles for medical imaging applications. Due to the highly transparent optical window for organic tissues in the near infrared region (650–1000 nm), upconversion fluorescence allows near infrared wavelengths to penetrate deeply into tissues, which is useful in biomedical areas such as biodetection, activated phototherapy, and screening. Materials/method Upconversion nanoparticles based on LaNbO4 doped with Tm3+ and Yb3+ were prepared by the one-step industrial process called Spray Pyrolysis. Samples with different Tm3+:Yb3+ molar ratios (1:4, 1:8 and 1:16) were obtained. Results The X-ray powder diffractograms of all the samples displayed the typical peaks of a crystalline material (tetragonal phase). Emission bands emerged in the blue, red, and near infrared regions, and they corresponded to the Tm3+ 1G4 → 3H6 (475 nm), 1G4 → 3F4 (650 nm), 3F2,3 → 3H6 (690 nm), and 3H4 → 3H6 (803 nm) transitions, which indicated a two-photon absorption process. As for bio-labelling application, the results indicated that Yb3+ concentration was directly related to signal intensity. Conclusions The intensity of positive conversion emissions depends directly on Yb3+ concentration. The bio-labelling tests pointed to the potential application of these materials. The sample containing the highest amount of Yb3+ provided better results and was easier to detect than the standard sample.