Effects of V and Mn Colorants on the Crystallization Behavior and Optical Properties of Ce-Doped Li-Disilicate Glass–Ceramics Sandhya Jayaraman Rukmani,* Richard K. Brow, w and Signo T. Reis University of Missouri-Rolla, Materials Science and Engineering Department, Rolla, Missouri 65409 Elke Apel, Volker Rheinberger, and Wolfram Ho¨ land Ivoclar Vivadent AG, FL-9494, Schaan, Leichtenstein The critical cooling rate and fluorescence properties of lithium (Li) disilicate glasses and glass–ceramics, doped with 2.0 wt% CeO 2 and with up to 0.7 wt% V 2 O 5 and 0.3 wt% MnO 2 added as colorants, were investigated. The critical cooling rates, R c , of glass melts were determined using differential thermal analysis and were found to be dependent on the relative concentrations of V 2 O 5 and MnO 2 , decreasing from 25731 to 16731C/min. An- nealed glasses were heat treated first to 6701C, and then to 8501C to form Li metasilicate and Li disilicate glass–ceramics, respectively. The fluorescence intensities of the Ce-doped glasses and glass–ceramics decrease by a factor of 100 with the addition of the transition metal oxides. This optical quenching effect is explained by the association of the Ce 31 ions with the transition metal ions in the residual glassy phase of the glass–ceramics. I. Introduction G LASS–CERAMICS with desirable mechanical and chemical properties and esthetic qualities are used for dental pros- thetic applications. One of the first systems developed was based on Li 2 O–ZnO–SiO 2 compositions, and subsequent systems based on leucite and mica phases have been developed for den- tal restorations. 1 These first materials often possessed relatively low strengths that proved problematic for use in highly stressed dental restorations. Recent compositional modifications to lith- ium disilicate (LS 2 ) base glasses have yielded translucent glass– ceramics that are characterized by high strength, excellent chem- ical durability, and the esthetic appearance of natural teeth. 2 An interesting property of these LS 2 glass–ceramics is the high flex- ural strength due to an unusual microstructure that consists of plate-like crystals of lithium disilicate (Li 2 Si 2 O 5 ) that are ran- domly oriented to cause cracks to blunt or branch. 3 The for- mation of a transient phase of Li 3 PO 4 crystals precedes the crystallization of the desired LS 2 phases. 4 Information about the crystallization behavior of melts that form glass–ceramics is critical for understanding the develop- ment of important properties and for optimizing processing conditions. For example, measurements of the critical cooling rate (R c ) needed to quench a melt from above the liquidus tem- perature to form a crystal-free glass are useful for determining the effects of composition on the ease or difficulty of glass for- mation, an important consideration for developing well-crystal- lized glass–ceramics. 5 The conventional differential thermal analysis (DTA) method for determining the critical cooling rate is based on the detection of crystallization exotherms while cooling a melt from above the liquidus temperature at different rates; e.g., see Barandiaran and Colmenro 6 and Whichard and Day. 7 These methods are best for characterizing melts that pos- sess a substantial crystallization exotherm on cooling, but are less useful for compositions, like some lithium disilicate melts, that exhibit slow crystallization kinetics or possess small heats of crystallization. A modified DTA method of determining R c has been shown 8 to be useful for such melts. This technique uses the much larger crystallization exotherms that are detected on re- heating samples that are quenched from the melt at different rates. Quenched samples with greater residual glass contents will possess larger crystallization exotherms on reheating. One important goal for the design and manufacture of glass– ceramics for dental restorations is the development of a material that reproduces the visible appearance of natural teeth, including color, translucency, and fluorescence properties. The desirable translucency in LS 2 glass–ceramics is achieved by the control of the relative refractive indices and volume concentrations of the crystalline and residual glassy phases, 1 whereas color and fluor- escence are achieved by the addition of transition metal oxides and rare-earth oxides, respectively, to the base composition. Teeth have a bluish–white fluorescence when exposed to ultraviolet (UV) light, with emissions between 400 and 650 nm depending on the excitation wavelength. 9 Ce 31 ions have been used to simulate natural fluorescence in dental restoratives, 2 be- cause they fluoresce in a similar range (320–500 nm) depending on the excitation wavelength and the host matrices; e.g., see Mohapatra, 10 Martinez-Martinez et al., 11 and Zhang et al. 12 The spectroscopic properties of Ce 31 ions are well investigated in various phosphors, glasses, and crystals. Ce 31 ions in solids show efficient broadband fluorescence due to 4f–5d parity al- lowed electric dipole interactions. 13,14 Notable properties of Ce 31 ions are the fast decay rate and the high efficiency of the allowed 4f–5d transitions in the UV-visible region. Transition metal oxides can also contribute to the fluores- cence properties of inorganic materials. Manganese is a well- known activator in many crystals and glasses and the Mn 21 ion exhibits broadband emission characteristics. 15 Manganese emis- sion wavelengths range from green to red; the green emission is characteristic of Mn 21 in tetrahedral coordination, and the or- ange to red colors come from octahedrally coordinated Mn 21 , with intermediate colors from a combination of both species. 16 Caldino et al. 17 described the photoluminescence properties of Ce 31 and Mn 21 ions codoped in zinc metaphosphate glasses used as phosphors for UV (Ce 31 absorption)—to yellow (Mn 21 emission) frequency conversion. Borate glasses doped with Ce 31 , Tb 31 , and Mn 21 ions generate white light under UV ex- citation, 18 with Ce 31 (blue emission) transferring a part of its energy to Tb 31 (green) and Mn 21 (red). Inorganic vanadates also fluoresce at visible wavelengths. Alkaline earth and zinc pyrovanadates emit between 450 and 600 nm when excited by M. Davis—contributing editor Presented at the 8th International Symposium on Crystallization of Glasses and Liquids, Jackson Hole, USA. *Author is currently employed by Saint-Gobain High Performance Materials at their Northboro-Worcester R&D facility. w Author to whom correspondence should be addressed. e-mail brow@umr.edu Manuscript No. 22096. Received August 10, 2006; approved October 9, 2006. J ournal J. Am. Ceram. Soc., 90 [3] 706–711 (2007) DOI: 10.1111/j.1551-2916.2006.01403.x r 2007 The American Ceramic Society 706