Magnesium fluoride as low-refractive index material for near-ultraviolet filters applied to optical sensors
Journal article, 2020

This article describes the fabrication of MgF2 and MgO thin-film-based optical filters and compares the optical transmission of the filters over UV. The MgF2 thin-films were deposited by use of an e-beam technique and their optical properties were characterised by ellipsometry. The effect of substrate temperature on the optical properties was studied. The MgF2 optimum refractive indices were obtained with a substrate temperature between 200 °C and 300 °C. Optical simulations were performed to compare the performance of MgF2 and MgO in the fabrication of near-UV narrow bandpass optical filters. While MgO-based optical filters result in a higher transmittance peak intensity, especially at 350 nm, the MgF2 optical filters are narrower, present lower values of FWHM, a mean value of 20 nm. This feature could be especially relevant for specific applications on fluorescent optical sensors. Finally, a Fabry-Perot based on a MgF2/TiO2 optical filter was deposited, using an e-beam technique for the MgF2 thin-films and RF-sputtering technique for the TiO2 thin-films. The MgF2/TiO2 optical filter peak transmittance is approximately 70% close to 400 nm, as expected. The results are discussed with focus on applications in fluorescent optical sensors for peaks at 350, 370, 380 and 400 nm, respectively.

RF sputtering

Energy-dispersive X-ray spectroscopy

Optical transmittance

Electron beam


Optical sensors

Thin-film optical filters

Scanning electron microscopy

Near-ultraviolet range

Magnesium fluoride


M. F. Silva

University of Minho

S. Pimenta

University of Minho

J. A. Rodrigues

Student at Chalmers

J. R. Freitas

University of Minho

Mohammadamir Ghaderi

Chalmers, Microtechnology and Nanoscience (MC2), Electronics Material and Systems Laboratory

L. M. Goncalves

University of Minho

G. De Graaf

Delft University of Technology

Reinoud F. Wolffenbuttel

Delft University of Technology

J. H. Correia

University of Minho


0042-207X (ISSN)

Vol. 181 109673

Subject Categories

Atom and Molecular Physics and Optics

Other Materials Engineering

Condensed Matter Physics



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