Fabrication of Microcrystalline NaPbLa(WO4)(3):Yb3+/Ho3+ Phosphors and Their Upconversion Photoluminescent Characteristics

New triple tungstate phosphors NaPbLa(WO4)(3):Yb3+/Ho3+ (x = Yb3+/Ho3+ = 7, 8, 9, 10) are successfully fabricated by microwave assisted sol-gel synthesis and their structural and frequency upconversion (UC) characteristics are investigated. The compounds crystallized in the tetragonal space group I4(1)/a and the NaPbLa(WO4)(3) host have unit cell parameters a = 5.3927(1) and c = 11.7961(3) angstrom, V = 343.05(2) angstrom(3), Z = 4. Under excitation at 980 nm, the phosphors have yellowish green emissions, which are derived from the intense S-5(2)/F-5(4) -> I-5(8) transitions of Ho3+ ions in the green spectral range and strong F-5(5) -> I-5(8) transitions in the red spectral range. The optimal Yb3+ :Ho3+ ratio s revealed to be x = 9, which is attributed to the quenching effect of Ho3+ ions, as indicated by the composition dependence. The UC characteristics are evaluated in detail under consideration of the pump power dependence and Commission Internationale de L'Eclairage chromaticity. The spectroscopic features of Raman spectra are discussed in terms of the superposition of Ho3+ luminescence and vibrational lines. The possibility of controlling the spectral distribution of UC luminescence by the chemical content of tungstate hosts is demonstrated.