THE METHODOLOGY FOR DETERMINING LIGHT ABSORPTION COEFFICIENTS OF LUMINOPHORE POWDER YAG:CE3+ MICROPARTICLES AND ITS TECHNOLOGICAL SUPPORT

Abstract

The development of methods for photometric control of turbid media based on YAG:Ce3+ phosphor (luminophore) microcrystals in transparent matrices requires solving a number of technological problems in the manufacture of self-supporting films of the composite material, adequate measurement of their optical properties and calculation of the corresponding values of absorption indices. This general problem is solved in this work by developing original measuring equipment, elaborating a number of technological protocols and a calculation algorithm based on modelling in the concept of a composite film of a dispersion medium. It is proved that the production of a suspension of microparticles of YAG:Ce3+ powder in epoxy resin at reduced pressure using an original turbine microstirrer allows to obtain a homogeneous and degassed suspension with a low rate of solid particle deposition, efficient light absorption of excitation radiation and an increased level of quantum yield of luminescence. A methodology for manufacturing self-supporting films from the obtained suspension has been developed. Such films are characterised by a low scatter of colourimetric parameters on the surface due to their high spatial homogeneity. 5 ml of the suspension is enough to produce a set of 30 flat-parallel films with an area of up to 1 cm2 and a thickness of 110÷600 µm with an error not exceeding ±3 µm. On the basis of the matrix spectroradiometer НAAS-2000, a photometric measuring setup was developed and created, which, in addition to the spectroradiometer, includes an optical module and an LED blue light source with λmax= 456 nm to excite the luminescence of the light-converting composition layers. The elements of the optical module ensure that the solid angle of the source radiation corresponds to the numerical aperture of the receiver (Ω = 0.126 steradian) in the form of the end window of the fibre-optic cable of the spectroradiometer and cause the transmission of the image on a 1:1 scale. An algorithm for determining the volumetric and linear absorption coefficients of a microcrystal-averaged YAG:Ce3+ phosphor powder under conditions corresponding to the isotropic scattering mechanism was proposed and worked out. Calculations in the composite film model, which takes into account the effects of light absorption and reflection by individual microcrystals in the volume of a transparent matrix, using the results of experimental measurements, allowed us to establish the values of the volume and linear absorption coefficients of the size-averaged (5.3 μm) YAG:Ce3+ microcrystal, which are 774 cm-1 and 129 cm-1, respectively.