Luminescence properties of doped with europium(iii) ions K3Bi5(PO4)6 phosphates

Abstract

Abstract. The efficient use of energy is one of the key problems for today. Taking into account that a significant part of the energy is spending on the needs of lighting, the improvement of lighting devices is an important technical and scientific task. Improvement of the modern lighting devices, which are LED lamps, can be performed in accordance with the requirements of a specific application, in particular, by selecting of an effective luminescent coating. This paper presents the results of the studies of the photoluminescence properties of the K₃Bi₅(PO₄)₆ compound doped with Eu³⁺ ions. In accordance with the crystallographic data, there are three positions in the structure of this compound that occupy bismuth ions and can be occupied by Eu³⁺ ions. It was established that at room temperature and photoluminescence excitation at 473 nm, the K₃Bi_5-xEu_x(PO₄)₆ samples reveal intensive luminescence in the spectral range of 575-700 nm. At low concentrations of Eu³⁺ ions (x <1), both the emission bands of the Eu³⁺ ions and the broad emission band of the K₃Bi₅(PO₄)₆ host are observed. The most intensive emission bands of Eu³⁺ ions are located in the spectral ranges 583–603 nm and 603– 635 nm, and can be associated with the radiative transitions ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂, respectively. The intensity of this luminescence and the luminescence of the matrix depend on the concentration of the activator. In the photoluminescence spectra, two bands of the ⁵D₀ → ⁷F₀ transitions are also observed, that indicates the presence of at least two low-symmetry positions of Eu³⁺ ions. The wide emission band of the matrix has a maximum at 520 nm and spreading on the spectral range of 500-700 nm. The possibility of using these compounds as luminescent materials for light sources in the greenhouse cultivation of plants is analyzed in this paper. It was established that from the viewpoint of overlapping of the absorption spectra of chlorophylls and photoluminescence spectra of the K₃Bi_5-xEu_x(PO₄)₆ samples under study, the most promising is the K₃Bi₄Eu₁(PO₄)₆ compound. The broad luminescence band of the matrix is absent, and the ratio of the intensities of the transitions I(⁵D₀ → ⁷F₂)/I(⁵D₀ → ⁷F₁) is the highest for the K₃Bi₄Eu₁(PO₄)₆. It is likely that a better overlap of the absorption spectra of chlorophylls and the emission of the K₃Bi_5-xEu_x(PO₄)₆ compound is possible for samples with concentrations 0.1 <x <2.5.

Key words: photoluminescence, potassium-bismuth phosphate, red phosphor, Eu³⁺