ABSTRACT
Tm3+/Yb3+ codoped LaVO4 and GdVO4 phosphors are successfully synthesized using solid state reaction methods and then upconversion emission studies are performed. X-ray diffraction has confirmed a pure monoclinic phase of LaVO4 and a tetragonal phase of GdVO4. Upconversion emission through 980 nm laser diode excitation has shown a strong blue band at 475 nm and two weak red bands at 647 and 700 nm originating from 1G4 â 3H6, 1G4 â 3F4 and 3F3 â 3H6 transitions of Tm3+ ions, respectively. Non-thermally coupled levels viz.3F3 (700 nm) and 1G4 (475 nm) in both the phosphors are used for fluorescence intensity ratio based optical thermometric studies and a comparison is made. The FIR data against temperature were fitted with polynomial and exponential fittings. The results show that polynomial fitting has a higher absolute sensitivity of 21.2 × 10-3 K-1 at 653 K for the LaVO4: Tm3+/Yb3+ phosphor than the exponential fitting sensitivity of 19.0 × 10-3 K-1 at 653 K, while in the case of the GdVO4: Tm3+/Yb3+ phosphor both fitting functions provided the same value of absolute sensitivity, that is 13.0 × 10-3 K-1 at 653 K. A comparison of the sensitivity values shows that the LaVO4: Tm3+/Yb3+ phosphor provides higher sensitivity than the GdVO4: Tm3+/Yb3+phosphor but the latter one is too high in upconversion emission.
ABSTRACT
In this work, a CaYF5:Ho3+/Yb3+ upconversion phosphor was synthesized and its structural, morphological, and optical properties were studied. The upconversion emission study was performed at an excitation pump power density of 5 W cm-2 and emissions at 544 nm, 650 nm and 747 nm due to the 5F4(5S2) â 5I8, 5F5 â 5I8 and 5F4(5S2) â 5I7 transitions of the Ho3+ ion, respectively were observed. From temperature-dependent upconversion spectra temperature sensitivity was calculated and sensitivity is found to be 14 × 10-3 K-1 for the synthesized upconversion phosphor. The photothermal conversion efficiency of the prepared sample in ethanol medium was tested. Moreover, the sample was used to develop latent fingerprints on various surfaces and good contrast in recorded images is observed. The invisible ink was prepared using the upconversion phosphor and then written words were recorded in upconversion emission mode.
ABSTRACT
By utilizing the effective energy transfer from Ce3+ to Yb3+, Er3+ and from Yb3+ to Er3+ authors have achieved dual mode emission in Y3Al4GaO12 activated with Ce3+/Yb3+/Er3+ ions. Surface morphological and elemental compositions of the prepared samples have been examined using field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDS) analysis, respectively. The chemical state of the dopant ions is confirmed by the X-ray photoelectron spectroscopy (XPS). On excitation with 438 nm the prepared material has shown broad visible emission band around 511 nm due to the electronic transition of Ce3+ ion. In addition to this sample has also shown NIR emission bands centered around 1024 nm and 1480 nm from Yb3+ and Er3+ ions, respectively. The emission band at 1024 nm could be due to the quantum cutting (QC) process. Furthermore, up-conversion (UC) emission against temperature and laser power variations is studied on 980 nm excitation wavelength. The prepared sample is used to fabricate visible and NIR LED devices by coating of sample on blue LED chip. Along with this demonstration, optical thermometry ability of the material is studied using emission intensity ratio of two emitting levels. Studies suggest that the prepared material could be useful as dual mode emitting phosphor and LED.
