Effect of Synthesis Techniques on the Optical Properties of Ho³⁺/Yb³⁺ Co-doped YVO₄ Phosphor: A Comparative Study

Abstract

The Ho 3+ /Yb 3+ -codoped YVO 4 phosphors have been synthesized by three different techniques (viz., solution combustion, sol–gel, and solid-state reaction techniques). X-ray diffraction patterns confirm the formation of a pure phase in the samples synthesized by all of the three methods; however, the average crystallite sizes in the three cases are different. The crystallite size increases if they are heated to higher temperature. The particle sizes are measured by scanning electron microscopy, which shows an increase in particle size with increasing the calcination temperature. The vibrational behavior of all of the three synthesized phosphor samples is studied by the Fourier transform infrared (FTIR) technique. The UV–vis absorption measurements give a large number of bands in all of the three samples prepared by three different methods. The upconversion (UC) emissions in all three samples have been monitored using a 980 nm diode laser. It gives an intense red emission in all of the three samples. Upconversion emission intensity is more prominent in the phosphor sample synthesized by the sol–gel technique and heated at 1473 K. The enhancement in UC emission intensity is well understood by the shape and size of the particles and also confirmed by the FTIR and UV–vis measurements. It is interesting to note that whereas UC measurements give red and weak green emissions, downshifting (DS) measurements show intense green, weak red, and broad blue emissions on UV excitation (323 nm). The DS behavior shows the same characteristics of the enhancement in overall emission. Overall, the phosphor sample synthesized by the sol–gel method gives better results in upconversion and downshifting behaviors when heated at 1473 K.

Brilliant Nonlinear Optical Response of Ho3+ and Yb3+ Activated YVO4 Nanophosphor and Its Conjugation with Fe3O4 for Smart Anticounterfeit and Hyperthermia Applications

“…This is related to the allowed transition of V–O CTB . The sharp peaks with small intensities due to Ho 3+ at 360, 425, and 455 nm are observed. , …”

“…The green (∼550 nm), red (∼650 nm), and NIR (∼755 nm) emission bands associated with 5 F 4 , 5 S 2 → 5 I 8 , 5 F 5 → 5 I 8 , and 5 F 4 , 5 S 2 → 5 I 7 electronic transitions of the Ho 3+ ion, respectively, are observed. 15,16 The emission spectra are monitored at different excitation wavelengths at 260, 290, 300, and 455 nm. Each excitation shows the emission peaks due to Ho 3+ .…”

“…8 The sharp peaks with small intensities due to Ho 3+ at 360, 425, and 455 nm are observed. 15,16 In order to see the concentration-dependent luminescence, different amounts of Ho 3+ are doped into the YVO 4 host at a fixed concentration of Yb 3+ (10 at. %).…”

“…% Yb 3+ ) at different laser powers are shown in Figure a. The UC spectra exhibit emission bands at ∼550 nm (green = G), ∼650 nm (red = R), and ∼755 nm, and these bands arise, respectively, due to 5 F 4 , 5 S 2 → 5 I 8 , 5 F 5 → 5 I 8 , and 5 F 4 , 5 S 2 → 5 I 7 electronic transitions of the Ho 3+ ion. , Here, Yb 3+ ions are acting as sensitizers that has a higher absorption cross section as compared to Ho 3+ at 980 nm excitation. The absorption cross section of Yb 3+ is 11.7 × 10 –21 cm 2 at 980 nm excitation. ,− The number of photons involved in the UC is calculated and plotted as shown in Figure b.…”

“…On the other hand, RE ions show very weak absorption due to the forbidden transition of f–f as well as self-quenching among them, and consequently, their emission intensity is very weak. , One of the RE ions having green (550 nm) and red (650 nm) emission is Ho 3+ , and this ion has absorption peaks at 425 and 455 nm, which fall in the broad emission band of V–O CT. Thus, resonance energy transfer (ET) occurs from VO 4 3– ions to Ho 3+ ions through a nonradiative process, and thereby strong emission from Ho 3+ ions occurs at 550 and 650 nm. − Thus, RE ions such as Ho 3+ and Eu 3+ ions have been doped into YVO 4 to enhance luminescence intensity. − Au nanoparticles conjugated with upconversion (UC) nanoparticles NaYF 4 :Er 3+ /Yb 3+ exhibit a strong fluorescence ET or Förster ET mechanism. Here, the absorption band of Au (surface plasmon resonance absorption peak at 542 nm) overlaps with the emission band of Er 3+ (emission peak at 540 nm) .…”