Examining phosphor material properties for imaging purposes: the role of the complex refractive index in the optical diffusion performance

Abstract

The scope of the present work was to evaluate the role of the complex refractive index in optical diffusion studies for imaging purposes. In particular, phosphor materials and their corresponding optical transmission characteristics play significant role in x-ray detectors, cathode ray tubes, microscopy techniques, white LED applications and have an impact on other scientific fields including chemical, energy, optoelectronic and space industries. The complex refractive index is associated with the optical attenuation capabilities of phosphor materials, either scattering or absorption, which in turn influences their imaging characteristics. In order to examine the complex refractive index effects, a simulation model was developed by taking into account the following: (i) phosphors of different layer thickness, 100 μm (thin layer) and 200 μm (thick layer), (ii) packing density 50%, (iii) three values of light wavelengths 400, 550, and 700 nm, and (iv) particle diameter in the range 10–10 mm. The complex refractive index was considered to vary: (a) from 1.5 up to 2.0 the real part and (b) from 10−6 up to 10−4 the imaginary part. The role of the complex refractive index on the optical parameters was examined within the framework of Mie scattering theory. Optical diffusion was assessed through Monte Carlo simulation techniques and the most important conclusion of the results was the achievement of improved phosphor spatial resolution by increasing the real part of the refractive index and not the imaginary one.