Nanophosphor Coatings: Technology and Applications, Opportunities and Challenges

Abstract

The particle size of conventional commercial phosphor powders used in lighting and displays is in the range from several micrometers to tens of micrometers and it is known that submicrometer-sized phosphors can facilitate a decrease in their consumption and improved resolution of phosphor screens. When the particle size becomes comparable to wavelengths of light, the optical properties of phosphor powders undergo remarkable qualitative changes so that the luminescence performance of nanophosphor screens, along with a very pronounced influence of the particle size, becomes dependent on several additional parameters such as packing density of nanoparticles, refractive index and chemical composition of the medium between them. This brings about both advantages and disadvantages which are discussed in this review of recent literature on the synthesis, deposition, and applications of nanophosphors.

Light Emission Intensities of Luminescent Y2O3:Eu and Gd2O3:Eu Particles of Various Sizes

“…Therefore, even the smallest of our particles do not give evidence that quantum confinement could improve luminescence performance. In contrast, studies have shown that the large surface area of nanoparticles host recombination centers and have adsorbates like water which quench luminescence [4]. The proposed effect of multiphonon emission competing with down conversion processes due to increased surface areas external and internal to the particles explains the decrease in luminescence as the particle size decreases.…”

“…In the display technology field, smaller particles are expected to improve resolution by combining the field emission of electrons with the cathodoluminescence of the particles [4,5,6,7,8,9,10]. For particles less than 10 nm in diameter, the possibility of exploiting quantum confinement effects with their respective changes in electron transitions and spectral details [2,11,12] have been reported.…”

“…For particles less than 10 nm in diameter, the possibility of exploiting quantum confinement effects with their respective changes in electron transitions and spectral details [2,11,12] have been reported. Moreover, colloidal processing allows the production of deagglomerated nanoparticles to obtain fluorescent transparent dispersions that have applications such as security marks, as well as biomarkers [4,13,14,15,16,17]. Some of these cited studies hint that small particles emit more light than large ones, however, these studies are usually based on the comparison of only two [7] or very few particle batches [18] and single excitation methods.…”

“…Some of these cited studies hint that small particles emit more light than large ones, however, these studies are usually based on the comparison of only two [7] or very few particle batches [18] and single excitation methods. In contrast, more fundamental studies report that smaller particles have lower emission intensity [3,4,9,19,20]. Specifically, Jing et al have shown a clear trend in Eu doped yttrium oxide particles in a size range from 100 to 900 nm and have compared them to 3 µm commercial particles under electron beam excitation to show increasing luminescence with increasing particle size [21].…”

“…Specifically, Jing et al have shown a clear trend in Eu doped yttrium oxide particles in a size range from 100 to 900 nm and have compared them to 3 µm commercial particles under electron beam excitation to show increasing luminescence with increasing particle size [21]. However, besides inner particle effects, overall optical mechanisms such as scattering in particle packing have to be considered before assessing the performance of particulate phosphor screens [3,4,21]. …”