Trivalent zirconium and hafnium ions in yttria-based transparent ceramics

Abstract

During the synthesis of ceramics based on Y 2 O 3 (yttria), it is common practice to use dioxides of tet ravalent ions (ThO 2 , ZrO 2 , HfO 2 ) as sintering addi tives, which simultaneously favor an increase in the transparency of ceramics. In particular, Yttralox-a ceramic material created by General Electric Co. (United States)-consists of 90 mol % Y 2 O 3 and 10 mol % ThO 2 and is close to glass with respect to transmission in the visible spectral range [1]. Russian specialists [2,3] have developed a technology of yttria based ceramics with additives of 10 mol % ZrO 2 or HfO 2 , which are characterized by a transmission of 86 or 82%, respectively, at a wavelength of 6 μm. These ceramics are used in bulbs for high pressure lamps of elevated brightness. Ceramics activated by rare earth ions can also be used as active elements of solid state lasers. Highly transparent modified Yttralox ceramics (Y 2 O 3 with additives of 10 mol % ThO 2 and 1 mol % Nd 2 O 3 ) [4] was used to create the first polycrystalline ceramic lasers [5], although their efficiency was relatively low. Investigations aimed at creating more effective laser ceramics were continued, and new yttria based com positions with ZrO 2 and HfO 2 additives were created [6][7][8]. It was found [7] that the optimum ZrO 2 content in these ceramics for highly effective lasing is about 3 mol %. However, it was a priori believed that additive metal ions (Th, Zr, Hf) occur in the lattice in tetrava lent states not forming centers of luminescence and absorption.In recent years, ZrO 2 and HfO 2 additives have been introduced into yttria activated by rare earth ions in order to produce disordering of the crystal structure of ceramic grains, which ensures broadening of the amplification band of activator ions. These ceramics are promising materials for the active media of lasers generating ultrashort radiation pulses. In particular, it was shown [8,9] ) 0.12 as compared to that in the analogous zirconia free ceramics [9]. However, to the best of the authors' knowledge, no data were reported on the possible presence of trivalent zirco nium and hafnium ions in high transparency yttria based ceramics with additives of these elements.The aim of the present work was to use the electron paramagnetic resonance (EPR) method for determin ing the presence of trivalent zirconium and hafnium ions in high transparency yttria based ceramics.

Optical Transparency and Local Electronic Structure of Yb-Doped Y2O3 Ceramics with Tetravalent Additives

“…In this situation, the control over the formation of oxygen vacancies and changes in their content, depending on the conditions of synthesis, becomes of particular importance. It was shown in [20] that this control can be performed indirectly by measuring the paramagnetic resonance spectra, which show the presence of trivalent hafnium and zirconium ions in Yb:Y 2 O 3 + 6HfO 2 and Yb:Y 2 O 3 + 6ZrO 2 . In the present paper, it is shown that the relative content of defective oxygen can be determined directly by measuring X-ray photoelectron O 1s spectra, which allows for choosing the most optimal annealing conditions to obtain the maximum optical transparency of ceramics.…”

Fabrication of high‐efficiency Yb:Y2O3 laser ceramics without photodarkening

“…It was identified that the photodarkening effect is caused by using the tetravalent Zr 4+ as the sintering additive. The charge imbalance between the Zr 4+ and Y 3+ induces the formation of $${\rm{Zr}}_{\rm{Y}}^ \cdot $$ point defects, which act as acceptors 20 . The electrons of the excited laser ions can be trapped by the Zr 4+ acceptors and decrease the laser oscillation efficiency.…”

“…The charge imbalance between the Zr 4+ and Y 3+ induces the formation of Zr ⋅ Y point defects, which act as acceptors. 20 The electrons of the excited laser ions can be trapped by the Zr 4+ acceptors and decrease the laser oscillation efficiency. In the meantime, a Zr 4+ bound with an electron and forms a Zr 3+ color center, 25 which is responsible for the photodarkening observed on the laser ceramics.…”

“…The charge imbalance between them induces Zr ⋅ Y ∕Zr ⋅ Lu point defects, which behave as acceptors in the ceramics. 20 In a previous paper, we have also reported the observation of a kind of photodarkening effect in the sesquioxide-based laser ceramics with ZrO 2 as a sintering additive. 21 It was identified that the occurrence of photodarkening phenomenon is related to using ZrO 2 as a sintering additive for the ceramics.…”

“…Zr 4+ has different valence state compared with Y 3+ /Lu 3+ ions. The charge imbalance between them induces $${\rm{Zr}}_{\rm{Y}}^ \cdot /{\rm{Zr}}_{{\rm{Lu}}}^ \cdot $$ point defects, which behave as acceptors in the ceramics 20 . In a previous paper, we have also reported the observation of a kind of photodarkening effect in the sesquioxide‐based laser ceramics with ZrO 2 as a sintering additive 21 .…”