Photon up‐converting (Yb,Er)2O3 thin films by atomic layer deposition

We report up‐converting (Yb,Er)2O3 thin films grown with the atomic layer deposition (ALD) technique. The films are crystalline and show a homogeneous morphology with a roughness less than 1 nm for 40 nm thick films. High‐intensity near‐infrared (NIR) to green and red two‐photon up‐conversion emission is obtained with 974 nm excitation through an absorption by Yb3+, followed by a Yb3+‐Er3+ energy transfer and emission from Er3+. The ALD technique promises to be excellent for producing up‐converting films for many applications such as near‐infrared radiation absorbing layers for solar cells and sensors in point‐of‐care biomedical diagnostics. Schematic picture of the ALD‐grown (Yb,Er)2O3 thin film including the up‐conversion emission spectra. Photon up‐converting materials are able to convert near infrared radiation to visible or even ultraviolet radiation and therefore they are under high demand for applications such as biolabelling and bioimaging. Many applications could benefit if the materials were prepared directly as thin surface coatings. Atomic layer deposition offers the possibility to prepare up‐conversion thin films with precise thickness and large area homogeneity.