Tm³⁺, Yb³⁺activated ANbO₄(A  =  Y, Gd, La) phosphors: a comparative study of optical properties (downshifting and upconversion emission) and laser induced heating effect

Abstract

A comparative study of optical properties and laser induced heating effects in Tm 3+ , Yb 3+ doped YNbO 4 , GdNbO 4 and LaNbO 4 phosphors is presented in this work. The phosphors were structurally characterized by x-ray diffraction and scanning electron microscopy measurements. The vibrational structures of the phosphors were studied using FTIR measurements. The optical band gaps (E g), calculated from the Wood and Tauc plot, are found to be 3.78, 4.50 and 3.27 eV for YNbO 4 , GdNbO 4 and LaNbO 4 , respectively. The luminescence property (downshifting (DS) and upconversion (UC)) was studied in the powder and the pellet forms of the phosphor samples. The DS emission of Tm 3+ doped ANbO 4 phosphors (λ ex = 265 nm) consists of broad blue emission due to (NbO 4) 3− group overlapped with sharp peaks due to f-f transition of Tm 3+ ion with most prominent emission one in the case of YNbO 4 phosphor. The DS emission is comparatively more intense in the pellet form. The NIR excited UC emission spectra of Tm 3+ , Yb 3+ co-doped ANbO 4 phosphors contain intense blue and NIR emissions due to the Tm 3+ ion. Contrary to the DS study, the best UC result is found for LaNbO 4 phosphor in pellet form. Further, the laser induced heating effect in UC emission with respect to laser pump power and irradiation time has also been studied in Tm 3+ , and Yb 3+ co-doped ANbO 4 phosphors. It was found to be more effective in the case of the YNbO 4 host where the heating effect is more prominent in the powder sample. We discuss the mechanisms involved in these observations in detail.

Optical transition and luminescence properties of Sm3+‐doped YNbO4 powder phosphors

“…Each spectrum can be divided into two parts. The first part comprises of a strong and broad band located at 200‐300 nm originating from the absorption of , which indicates that there is an efficient energy transfer from groups to Sm 3+ . The second part ranging from 300 to 550 nm contains a series of sharp peaks corresponding to the transitions 6 H 5/2 to 3 H 7/2 (350 nm), 4 F 9/2 (367 nm), 4 D 5/2 (379 nm), 4 K 11/2 (408 nm), 4 P 5/2 / 4 M 19/2 (420 nm), 4 G 9/2 / 4 I 15/2 (442 nm), 4 F 5/2 / 4 I 13/2 (468 nm), 4 I 11/2 / 4 M 15/2 (483 nm), 4 F 3/2 (500 nm), and 4 G 5/2 (526 nm) of Sm 3+ ion, respectively …”

Photoluminescence behavior of rare earth doped self-activated phosphors (i.e. niobate and vanadate) and their applications

“…3 shows the UC emission behavior of the rare earth (Ho 3+ /Yb 3+ and Tm 3+ /Yb 3+ ) doped YNbO 4 , GdNbO 4 and LaNbO 4 phosphors in the visible region on excitation with a 980 nm diode laser. 25,[28][29][30] Intense green and moderately weak red emissions are observed in the GdNbO 4 :Ho 3+ ,Yb 3+ phosphor, as shown in Fig. 3(a), in which optimization was performed to get intense UC emission by varying the concentrations of Ho 3+ and Yb 3+ ions, shown in the inset of the gure.…”

“…GdNbO 4 is known as a self activated compound which has a charge transfer band (CTB) in the UV region and gives blue emission upon UV excitation. 25,30 In GdNbO 4 , the niobate group [(NbO 4 ) 3− ] acts as a uorescence center in the matrix and gives blue emission under UV excitation. In the previous section, it was observed that there is a broad CTB at 266 nm and also a broad blue emission at 442 nm due to the (NbO 4 ) 3− group since the resonance condition of CET from (NbO 4 ) 3− to Yb 3+ ion is well satised.…”

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

“…It has been reported in the literature that heating becomes more prominent at higher pump power and multiphonon relaxation increases. 25,26 Due to this, the relaxation from the green-emitting level to a lower-lying redemitting level increases. Thus, the intensity of red emission increases.…”