K 5 Eu(MoO 4 ) 4 red phosphor for solid state lighting applications, prepared by different techniques

• Published in: CrystEngComm 2023-01, Vol.25 (5), p.835-847
• Main Authors: Posokhova, Svetlana M., Morozov, Vladimir A., Deyneko, Dina V., Redkin, Boris S., Spassky, Dmitry A., Nagirnyi, Vitali, Belik, Alexei A., Hadermann, Joke, Pavlova, Erzhena T., Lazoryak, Bogdan I.
• Format: Article
• Language: English
• ISSN: 1466-8033; 1466-8033
• DOI: 10.1039/D2CE01107G

The influence of preparation techniques on the structure and luminescent properties of K 5 Eu(MoO 4 ) 4 (KEMO) was investigated. KEMO phosphors were synthesized by three different techniques: solid state and sol–gel (sg) methods as well as the Czochralski (CZ) crystal growth technique. Laboratory powder X-ray diffraction (PXRD) studies revealed that all KEMO samples had a structure analogous to that of other high temperature α-K 5 R(MoO 4 ) 4 palmierite-type phases (space group (SG) R 3̄ m ). Contrary to laboratory PXRD data, electron diffraction revealed that the KEMO crystal grown by the CZ technique had a (3 + 1)D incommensurately modulated structure (super space group (SSG) C 2/ m (0β0)00) with the modulation vector q = 0.689 b *. A detailed analysis of electron diffraction patterns has shown formation of three twin domains rotated along the c axis of the R -subcell at 60° with respect to each other. Synchrotron XRD patterns showed additional ultra-wide reflexes in addition to reflections of the R -subcell of the palmierite. However, the insufficient number of reflections, their low intensity and large width in the synchrotron X-ray diffraction patterns made it impossible to refine the structure as incommensurately modulated C 2/ m (0 β 0)00. An average structure was refined in the C 2/ m space group with random distribution of K1 and Eu1 in [M1 A 2 O 8 ]-layers of the palmierite-type structure. The dependence of luminescent properties on utilized synthesis techniques was studied. The emission spectra of all samples exhibit intense red emission originating from the 5 D 0 → 7 F 2 Eu 3+ transition. The integrated intensity of the emission from the Eu 3+ 5 D 0 term was found to be the highest in the crystal grown by the CZ technique. The quantum yield measured for KEMO crystals demonstrates a very high value of 66.5%. This fact confirms that KEMO crystals are exceptionally attractive for applications as a near-UV converting red phosphor for LEDs.