Magnesium fluoride as low-refractive index material for near-ultraviolet filters applied to optical sensors
Artikel i vetenskaplig tidskrift, 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.

Magnesium fluoride

RF sputtering

Near-ultraviolet range


Optical transmittance

Energy-dispersive X-ray spectroscopy

Scanning electron microscopy

Optical sensors

Electron beam

Thin-film optical filters


M. F. Silva

Universidade do Minho

S. Pimenta

Universidade do Minho

J. A. Rodrigues

J. R. Freitas

Universidade do Minho

Mohammadamir Ghaderi

Chalmers, Mikroteknologi och nanovetenskap (MC2), Elektronikmaterial och system

L. M. Goncalves

Universidade do Minho

G. De Graaf

TU Delft

Reinoud F. Wolffenbuttel

TU Delft

J. H. Correia

Universidade do Minho


0042-207X (ISSN)

Vol. 181 109673


Atom- och molekylfysik och optik

Annan materialteknik

Den kondenserade materiens fysik



Mer information

Senast uppdaterat