Optical properties of Tm3+/Yb3+ co-doped XAl2O4 (X = Mg, Ca, Sr and Ba) phosphors: Effect of co-doping of alkaline earths on the radiative as well as non-radiative behaviours

Abstract

Listen

Translate article

• Effects of Alkaline Earth ions on radiative as well as non-radiative relaxations have been monitored. • The blue UC emission intensity of CAO: Tm, Yb phosphor enhances upto 10 times in presence of Mg 2+ ion. • The high spectral and color purity of CAO: Tm, Yb, 10Mg phosphor have been achieved which suggests this material as pure blue upconverter. • In non-radiative relaxation, laser induced optical heating confirms that incorporation of Mg 2+ ion increases the radiative process. Tm 3+ - Yb 3+ co-doped alkaline earths aluminate phosphors of the type XAl 2 O 4 (X = Mg, Ca, Sr and Ba) are synthesized using solid state reaction method. The crystal structure and the phase of all these phosphor materials are confirmed by X-ray diffraction (XRD) measurements. The surface morphologies of all the samples are monitored by Scanning Electron Microscope (SEM) technique. The Ultraviolet (UV)-visible-near-IR region (NIR) absorption spectra show sharp f-f electronic transitions of Tm 3+ and Yb 3+ ions which are more prominent in CaAl 2 O 4 :Tm 3+ ,Yb 3+ phosphor. The upconversion (UC) emission spectra of the samples have been measured which give intense blue and NIR emissions on excitation with 980 nm radiation. It is observed that CaAl 2 O 4 :Tm 3+ ,Yb 3+ phosphor gives better UC emission in blue as well as NIR region than the others. We have also monitored the UC emission spectra of CaAl 2 O 4 :Tm 3+ , Yb 3+ in the presence of other alkaline earths metals (i.e. Mg 2+ , Sr 2+ and Ba 2+ ions) as sensitizer. It is found that Mg 2+ ion is a better enhancer for UC emission in CaAl 2 O 4 :Tm 3+ ,Yb 3+ phosphor (upto ten times) than the others. The spectral and color purity are found to be maximum for CaAl 2 O 4 :Tm 3+ ,Yb 3+ ,10Mg 2+ phosphor. The laser induced optical heating is observed quantitatively in CaAl 2 O 4 :Tm 3+ ,Yb 3+ ,xMg 2+ (x = 0, 5, 10 and 15 mol%) phosphors on excitation with 980 nm radiation. Thus, the maximum color and spectral purity for blue region in CaAl 2 O 4 :Tm 3+ ,Yb 3+ ,Mg 2+ phosphor may be applicable as blue LED as well as the laser induced optical heating can be used for the application in cancer treatment based on opto-thermal therapy and as an optical heater.