In recent years, various optical devices such as solid-state lasers and scintillators have been applied in many fields including manufacturing, medicine, and communications, because of which the demand for higher output and larger sizes is increasing. These performances are highly dependent on the characteristics of the used fluorescent and transparent materials used, which should have high thermal and mechanical durability. α-SiAlON ceramics are expected as novel optical materials because of their excellent thermal, mechanical properties and intrinsic transparency due to high band gap energy. Furthermore, α-SiAlON ceramics doped with rare-earth ions such as Ce³⁺, Eu²⁺, Tb³⁺, Yb²⁺, and Er³⁺ have recently generated interest as a promising phosphor material. In our previous study, we have realized highly transparent Lu-α-SiAlON:Ce³⁺ ceramics by eliminating the scattering sources, such as pores, second phase, and coarser α-SiAlON particles, as well as the oxynitride glass as the absorption source. In this study, the photoluminescence and scintillation of the transparent Lu-α-SiAlON:Ce³⁺ ceramics was investigated.
The chemical compositions of the fabricated Lu-α-SiAlON:Ce³⁺ ceramics was (Lu_0.9Ce_0.1)_0.33Si_10.5Al_1.5O_0.5N_15.5. α-Si₃N₄, AlN, Lu₂O₃, and CeO₂ powders were weighed, and they were mixed with a dispersant by wet ball milling in ethanol for 48 h. Granules of the powder mixtures with added binder and lubricant were prepared by forced sieving through a nylon mesh with a 250 µm mesh opening. Subsequently, they were molded by uniaxial pressing at 50 MPa for 30 s, followed by 10 cycles of cold isostatic pressing at 200 MPa for 1 min to produce pellet-like green bodies of dimensions φ15 mm × 2 mm. After dewaxing, the green bodies were fired at 1600? for 4 h in 0.9 MPa N₂ using a gas-pressure sintering furnace.
The samples emitted blue light when irradiated with UV light (365 nm). In photoluminescence spectra measurements, there were broad emission peaks around 480 nm by excitation with 377 nm UV irradiation, which resulted from the 4f-5d transition of Ce³⁺. The excitation spectrum had two peaks around 290 nm and 396 nm, which overlapped with the emission spectrum. On the other hand, there were two peaks around 480 nm and 550 nm related to α-ray-induced luminescence, of which peak wavelength is longer than photoluminescence. The scintillation decay curve consists of two components whose decay constants are 48 ns and 652 ns. Although the scintillation properties of Lu-α-SiAlON:Ce³⁺ have not been reported, in consideration that previously reported scintillation materials with Ce³⁺ as the emission center have decay time constants of several tens of ns, the fast and slow decay component can be attributed to the 4f-5d transition of Ce³⁺ and defects in α-SiAlON, respectively. The light yield of the Lu-α-SiAlON:Ce³⁺ ceramics was 1300 photons 5.5 MeV^-1 as calculated from the pulse height spectrum measurement.