Effect of Ce³⁺ Concentration and YAG Crystal Particles Size on Photoluminescence

Abstract

Purpose of research. Determine the effect on the photoluminescence of phosphors from yttrium-aluminum garnet activated by cerium ions Ce3+, the size of its particles and the concentration of cerium ions in them.Methods. Structural electron and confocal microscopic, fluorescent, microspectral studies using a laser lex = 473 nm as an excitation source, energy dispersive, X-ray diffraction studies, as well as goniophotometric measurements on the radial distribution of light intensity excited by the LED matrix were carried out.Results. A detailed granulometric analysis of the particle sizes of phosphors was carried out for two samples from different manufacturers, cumulative distributions M(d) were constructed and their quantiles were established. Based on the results of measuring photoluminescence from individual particles in the compositions of phosphors based on YAG:Ce3+, a Stokes shift was detected in these samples: short-wavelength – for particles with sizes less than 10 μm and with low concentration and long-wavelength – with sizes greater than 10 μm with an increased concentration of over ~0.2% . The obtained microspectral size-emission dependences lem(d) and energy Imax(d) were consistent with the description based on the proposed physical mechanism of their formation by the 5d → 2F5/2 and 5d → 2F7/2 transitions.Conclusion. A short-wavelength shift of photoluminescence intensity maxima for particles smaller than 10 μm was discovered, due to a significant increase in the influence of surface stresses due to a reduction in the number of atoms. For larger particle sizes, the characteristic photoluminescence intensity maxima cease to depend on the wavelength. The radial distribution of luminous intensity determined by the goniophotometric method made it possible to calculate the value of the luminous flux equal to 1350 lm and 1140 lm, respectively, for LED matrices containing 8 LEDs with the studied phosphors.