Neeraj Kumar Giri

White light upconversion emissions from Tm3++Ho3++Yb3+ codoped tellurite and germanate glasses on excitation with 798 nm radiation

White light has been produced using 798 nm laser excitation in Tm3++Ho3++Yb3+ codoped tellurite and germanate glasses. These glasses simultaneously generate the three primary colors, red, green, and blue, on 798 nm excitation. Thus, multicolor emission obtained was tuned to white luminescence by adjusting the Ho3+ ion concentration and excitation power. UV excitation and fluorescence spectra of these triply doped glasses give additional emissions, which do not appear on 798 nm excitation.

Efficient blue upconversion emission in Tm3+ via energy transfer from Yb3+ doped in lithium modified tellurite glass

Intense blue and red upconversion emissions were obtained in Tm3+ doped tellurite glass when codoped with Yb3+ ions on pumping with 798nm radiation. The highest intensity of the blue emission was found for glasses with 0.5mol% Tm3+ and 6.0mol% Yb3+. From a study of the dependence of the upconversion intensity on excitation intensity, it is concluded that emissions are due to Tm3+ ions and involve cooperative energy transfer as well as energy transfer from Yb3+ to Tm3+ ions. Lifetime of the Tm3+ level, which is responsible for the intense blue emission, has been measured for various concentrations of Yb3+.

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.

Role of Yb3+ ions in the IR to visible upconversion of Er3+ ions in LTT glasses

In order to develop efficient visible upconversion lasers and optical fiber amplifiers, the detailed spectroscopic properties of singly doped Er3+ and codoped Er3+-Yb3+ ions in lead tungsten tellurite (LTT) glasses have been investigated. The glasses were prepared by the conventional melt quenching technique. Absorption, visible upconversion spectra and NIR emission spectra were recorded as a function of Yb3+ ions concentrations. Judd-Ofelt (J-O) analysis has been performed for the spectral intensities of Er3+and Er3+-Yb3+ absorption bands. Spontaneous emission probabilities (AR), radiative lifetimes (τR) and branching ratios (βR) were calculated by using the phenomenological Judd-Ofelt intensity parameters. Three strong upconversion emission bands centered at 526, 551 and 665 nm were observed under 980nm excitation, due to the energy transfer process from Yb3+ to Er3+ ions. The green emissions centered at 526 and 551 nm and the red emission at 665 nm are attributed to 2H11/2→ 4I15/2, 4S3/2→ 4I15/2 and 4F11/2→ 4I15/2 transitions of Er3+ions respectively. The relative intensity variations of 2H11/2→ 4I15/2, 4S3/2→ 4I15/2 and 4F9/2→ 4I15/2 transitions have been explained on the basis of the increase in the population accumulation rates of 2H11/2 ,4F9/2 and 4S3/2 levels. The peak stimulated emission cross-section (σe) and gain bandwidth parameter (σe×▵λeff) of 4I13/2 → 4I15/2 transition at 1.54 μm for Er3+ and Er3+-Yb3+ ions in LTT glasses have been determined and compared with different glass hosts. The stimulated emission cross-sections (σe) determined by using McCumber theory for the 4I13/2 → 4I15/2 transition are compared with the measured (σe) values obtained from the emission data. The results of these investigations revealed that the lead tungsten tellurite (LTT) glasses could be more useful as promising host materials for the design and development of optical fiber amplifiers and upconversion lasers.