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.
Keywords: Bioprobes; Infrared emission; Spray pyrolysis; Upconversion.
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