Upconversion photoluminescence properties of SrY2(MoO4)4:Er3+/Yb3+ phosphors synthesized by a cyclic microwave-modified sol–gel method

Preparation of PbLa2(MoO4)4:Er3+/Yb3+ particles via microwave sol–gel route and upconversion photoluminescence properties

“…1(e) when the doping concentration of Er 3 þ /Yb 3 þ is 0.02/0.18 mol%. A similar impurity phase was also observed in the case of Er 3 þ /Yb 3 þ doped co-doped CaLa 2 (MoO 4 ) 4 and SrY 2 (MoO 4 ) 4 phosphors when the doping concentration of Er 3 þ /Yb 3 þ is 0.02/0.18 mol% [7,9]. The foreign reflexes marked with an asterisk in Fig.…”

“…The foreign reflexes marked with an asterisk in Fig. 1(e) compared to the Er 3 þ /Yb 3 þ doped CaLa 2 (MoO 4 ) 4 and SrY 2 (MoO 4 ) 4 can be ascribed to the fact that Er 3 þ and Yb 3 þ ions are well substituted in the tetragonal-phase PbLa 2 (MoO 4 ) 4 of the scheelite-type structure and form a disordered structure by the incorporation of the Er 3 þ and Yb 3 þ elements into the crystal lattice [7,9,25]. In the crystal structure of PbLa 2À x MoO 4 , the La 3 þ ion site is supposed to be occupied by Er 3 þ and Yb 3 þ ions with fixed occupations according to the nominal chemical formulas.…”

“…With the decrease in the ionic radius of alkaline earth metal ions (R Ca o R Sr o R Ba ; R=ionic radius), the structure of MLn 2 (MoO 4 ) 4 could be transformed to a highly disordered tetragonal scheelite structure from the monoclinic structure. It is possible that that the trivalent rare earth ions in the disordered tetragonal-phase could be partially substituted by Er 3 þ and Yb 3 þ ions, and the ions are effectively doped into the crystal lattices of the tetragonal phase due to the similar radii of trivalent rare earth ions of R 3 þ , resulted in the excellent UC photoluminescence properties [7][8][9][10].…”

“…The Er 3 þ ion activator is the luminescence center of the UC particles, while the sensitizer enhances the UC luminescence efficiency [5,6,[8][9][10]. To prepare the double molybdates, several processes have been developed via specific preparation processes, including solid-state reactions [11][12][13][14][15], co-precipitation [16,17], the solgel method [4][5][6], the hydrothermal method [18,19], the Pechini method [20,21], organic gel-thermal decomposition [22], the microwave-assisted hydrothermal method [23] and the microwave sol-gel method [7,9]. For practical application of UC photoluminescence in products such as lasers, threedimensional displays, light-emitting devices, and biological detectors, features such as the homogeneous UC particle size distribution and morphology need to be well defined.…”

“…Microwave heating is delivered to the material surface by radiant and/or convection heating, which is transferred to the bulk of the material via conduction [24][25][26][27]. A microwave sol-gel process is a cost-effective method that provides high homogeneity and is easy to scaleup, and it is emerging as a viable alternative approach for the quick synthesis of high-quality luminescent materials [7,9,28,29]. However, the PbLa 2 À x (MoO 4 ) 4 :Er 3 þ /Yb 3 þ phosphors prepared by the microwave sol-gel method have not been reported.…”