Role of energy transfer, defect, and lattice dimension in photophysical characteristics of AWO ₄ :Nd ³⁺ (A=Ca, Sr and Ba)

Abstract

Abstract The fact that the scheelite based compounds are of high technological importance in the area of scintillator and optoelectronics, makes their detailed photophysical study relevant not only for fundamental material science but also in tailoring their optical properties for advanced applications. With this view, we have carried out a very systematic study on near infra‐red (NIR) emitting Nd 3+ doped CaWO 4 , SrWO 4 , and BaWO 4 compounds. Light emitting efficiency in AWO4:Nd 3+ is governed strongly by radiative/nonradiative properties, host‐dopant energy transfer (HDET) efficiency and defect density. We have used photoluminescence, positron annihilation, and photoacoustic (PA) spectroscopy to study the factors effecting light emission. These scheelites are known to exhibit self activated luminescence in visible region due to charge transfer within the tungstate group and wavelength maxima exhibited red shift as we move from Ca→Sr→Ba. This can provide a new strategy to achieve spectral tunability in AWO 4 scheelite by changing A 2+ ionic radius. The fractional intensity in the green region is least in the case of SrWO 4 samples suggesting that the oxygen vacancy density is minimal in case of SrWO 4 which is well‐supported by the positron annihilation lifetime spectroscopy (PALS). Based on our studies, we found that the HDET was highly efficient in CaWO 4 :Nd 3+ and minimal in BaWO 4 :Nd 3+ which get's reflected in photoluminescence intensity. Emission lifetimes are shorter in CaWO 4 and highest in SrWO 4 host which are in sync with positron annihilation lifetime values. Based on our results of PALS, it was found that CaWO 4 :Nd 3+ has the highest concentration of defects i.e. cation vacancies; so larger is the probability of nonradiative signals and hence higher PA intensity from it.