Anita Rai

Intense green and red upconversion emissions from Ho3+ in presence of Yb3+ in Li:TeO2 glass

Weak visible emission is observed at 545 nm and 660 nm on 976 nm excitation of Ho(3+) ions doped in tellurite glass. Addition of ytterbium to the doped glass causes a large increase in intensity of the green and the red emissions. In addition to these two new emissions of Ho(3+) one in the blue and the other in the NIR region are also observed. This increase in intensity is ascribed to energy transfer from ytterbium ions to holmium ions. Rate equation model has been proposed to study the upconversion emission and its dependence on pumping power. Possible upconversion mechanisms for these emissions are also discussed. Effect of changing the concentration of Yb(3+) on the emission intensity, lifetime and full width at half maximum (FWHM) in (5)F(4)((5)S(2)) --> (5)I(8) transition of Ho(3+) in codoped sample has also been studied.

Enhancement of upconverted luminescence in Er3+:TeO2 glass on increasing the temperature and concentration of Yb3+ beyond the critical limit

Enhancement of upconverted luminescence in Er3+∕Yb3+:TeO2 has been observed with increase in the concentration of Yb3+ on excitation with 780nm laser radiation. It is further noted that the upconversion is increased even above the quenching limit on increasing the temperature of the glass. The incident radiation excites Yb3+ indirectly via Er3+ resulting in a strong blue emission from Yb3+ and green and red emissions from Er3+. The UV emission from Er3+ at 380nm involves three near infrared photons when there is no Yb3+ in the glass but when Yb3+ is also present, this behaves as a two photon process. The lifetime of the S3∕24 level of Er3+ in glasses containing only Er3+ and also those containing both Er3+ and Yb3+ has also been measured in different conditions.