Abstract
A spectroscopic investigation of an extensive series of -doped and -codoped soda-lime-silicate (SL) and aluminosilicate (AS) glasses is presented. Compared to SL glasses, transitions in AS glasses show higher oscillator strengths, larger inhomogeneous broadening, and smaller crystal-field splittings of the respective excited-state multiplets. The excited-state relaxation dynamics is adequately described by a combination of the Judd-Ofelt model and the energy-gap law. With the exception of multiphonon relaxation is dominant for all excited states, making it possible to efficiently pump the 1.55 μm emission by excitation of at around 980 nm. The absolute luminescence quantum yield, for low 980-nm excitation density η, is at 0.4 mol % and drops to about 0.65 upon increasing to 1.2 mol %, indicating the onset of energy-transfer processes. Samples with high impurity concentration suffer from significantly higher quenching of luminescence at higher concentrations. Energy migration to the minority of ions coordinated to , followed by efficient multiphonon relaxation accounts for this effect. At low excitation densities, the strong near-infrared absorption of in combination with efficient energy transfer increases the population density in -codoped samples by up to 2 orders of magnitude compared to equivalent samples without . The dependence of η on codotation of 0.4 mol % -doped samples predicts that a minimum of is required to achieve efficient sensitization of by . The relative intensities of upconversion luminescence from and are used to analyze internal sample heating in detail. Due to the high absorption cross section of , increasing the concentration in -codoped samples of given length increases the absorbed power and subsequently the total density of multiphonon emission, leading to internal temperatures of up to 572 K in 0.4 mol % samples codoped with 4 mol % and excited with . Multiphonon relaxation from is shown to be inefficient even at these high internal sample temperatures. From upconversion luminescence spectra of a series of glasses, the thermal conductivity is estimated to be between and , in good agreement with the known value of for soda-lime-silicate glass.
- Received 28 August 1996
DOI:https://doi.org/10.1103/PhysRevB.56.9302
©1997 American Physical Society