The co-doping effect of Zr 4+ ions on upconversion (UC) luminescent properties in visible region of Y 2 O 3 : Er 3+ and Y 2 O 3 : Er 3+ , Yb 3+ sub-microcrystals prepared by urea precipitation method has been investigated under 980 nm excitation. Compared with the original Y 2 O 3 : Er 3+ and Y 2 O 3 : Er 3+ , Yb 3+ sub-microcrystals, the UC luminescence of sub-microcrystals with similar size was enhanced after Zr 4+ ions co-doping. The UC luminescent properties have been discussed in detail via luminescence spectra, decay curve analysis and a suitable energy level diagram. The enhancement mechanism of UC luminescence in the two series of Zr 4+ ions doped sub-microcrystals was attributed to the complex crystal field around Er 3+ ions caused by Zr 4+ ions co-doping. After Zr 4+ ions substituted Y 3+ ions and entered the crystal lattice, the charge mismatch and lattice distortion made the crystal field more complex. This research contributes to the understanding of UC luminescent properties of lanthanide (Ln 3+ ) ions doped UC materials and their technological applications in fields such as bioimaging, drug delivery, and optical temperature sensors.
Sm 3+ doped calcium stannate (CaSnO 3 :Sm 3+ ) and (Sm 3+ , Zr 4+ )-co-doped calcium stannate (CaSnO 3 :Sm 3+ , Zr 4+ ) photoluminescent phosphors were synthesized via co-precipitation and subsequent sintering in oxidizing atmosphere at 1400 °C for 60 min with SnCl 4 ·5H 2 O, CaCl 2 ·2H 2 O, ZrO(NO 3 ) 2 · x H 2 O and Sm 2 O 3 as main raw materials. The synthesized samples were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, photoluminescent spectroscopy, luminescent decay curves, afterglow spectroscopy and thermo-luminescent glow curves. The results show that CaSnO 3 pure phase is synthesized in co-precipitation reaction at an optimum molar ratio of CaCl 2 ·2H 2 O:SnCl 4 ·5H 2 O of 1.4:1.0 and subsequent sintering at 1400 °C for 60 min. Calcium stannate as a host matrix can be doped with Sm 3+ ions or co-doped with Sm 3+ /Zr 4+ ions for the formation of white photoluminescent phosphors. CaSnO 3 :0.03Sm 3+ phosphor has an optimum photoluminescent intensity. Also, the fluorescent emission intensity of CaSnO 3 :0.03Sm 3+ ，0.04Zr 4+ phosphor under excitation of 365 nm wavelength can be enhanced due to Zr 4+ ions doping at an optimum doping amount y of 0.04. The CIE 1931 chromaticity coordinates change from (0.3600, 0.3535) for CaSnO 3 :0.03Sm 3+ phosphor to (0.3622, 0.3574) for CaSnO 3 :0.03Sm 3+ , 0.04Zr 4+ phosphor as the average crystalline size decreases from 71.5 to 68.3 nm and the unit cell volume increases from 0.2686 to 0.2775 nm 3 . In addition, the electron transition mechanism for the photoluminescent and long afterglow properties was also discussed.
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