The comparison investigation of direct upconversion sensitization luminescence between ErYb:oxyfluoride glass and vitroceramics

This paper investigates and compares the direct upconversion sensitization luminescence of ErYb co-doped oxyfluoride glass (ErYb:FOG) and vitroceramics (ErYb:FOV) when excited by a 966-nm diode laser. It is found that there are splendid upconversion luminescence phenomena which are studied and analyzed carefully. (1) It is found that the direct sensitization upconversion luminescence L of ErYb:FOV is generally 10 times greater than that of ErYb:FOG. It is also interesting that not only blue light but also red light increases more vigorously than green light when pumping laser power increases. It results from the Er3+-Yb3+ ion's cluster effect. (2) For the ErYb:FOG, there is an obvious "characteristic" saturation phenomenon. That is, the F-P log-log curves of upconversion fluorescence vs. pumping laser power are basically rather good straight lines. The smaller the laser facula is, the smaller the slope of F-P log-log curves. This "characteristic" saturation phenomenon is mainly the result of strong energy diffusion among Yb3+ ions caused by the long-range correlation. For the ErYb:FOV, because of the small and uniform micro-crystallites with a size of about 10(1) nm, the sensitization action of Yb3+ ion to Er3+ ion is greatly enhanced. The "typical" saturation caused by population exhaustion is also very much increased and has great effect. (3) The most interesting phenomenon is at about 474 nm of ErYb:FOG (or 476.5, 468.5 nm of ErYb:FOV) cooperative radiation upconversion fluorescence oriented from a couple state of two Yb3+ ions' cluster! (4) Both ErYb:FOV and ErYb:FOG have a new kind of common "diffusion-transfer" upconversion mechanism, i.e., "energy diffusion" among Yb3+ ions sequentially followed by energy transfer between Er3+ and Yb3+ ions. (5) The passage of cluster effect upconversion induced by couple state of two Yb3+ ions' cluster could be described as (F-2(7/2)(Yb3+) + F-2(7/2)(Yb3+)) --> (F-2(5/2)(Yb3+) + F-5/2(Yb3+)) --> ((F5/2F5/2)-F-2-F-2 (Yb3+Yb3+)) --> ((F7/2F7/2)-F-2-F-2(Yb3+Yb3+)). To the best of our knowledge, similar mechanism has not been reported up to now. (C) 2000 Elsevier Science B.V. All rights reserved.