Lead halide perovskites (LHPs) have emerged in a variety of thin film optoelectronic applications such as light-emitting diodes, solar cells, and lasing owing to high photoluminescence quantum yield (PLQY), bandgap tunability, defect tolerance, and facile synthesis routes. LHP materials have also recently gained interest in the scintillator community due, in part, to comparatively low bandgap energies because of the inverse relationship between charge carrier generation in the hot electron impact ionization cascade process and the bandgap energy of the scintillator crystal.[1] Despite the corresponding high theoretical light yield, empirical data has remained marginal at non-cryogenic temperatures due to the thermal quenching of LHP excitons and self-absorption of excitonic emission.[2] Since scintillators must be sufficiently thick to attenuate high-energy photons, low self-absorption is critically important to extract scintillation light efficiently. Therefore, much like in traditional scintillator material systems, extrinsic luminescent dopants such as lanthanide ions are advantageous for increasing the stokes shift and obtaining high PLQY. In particular, work on the quantum cutting (i.e., two-photon emitting) CsPbCl3:Yb3+ system, originally sought for applications in ultraviolet down-conversion for photovoltaic (PV) light harvesting,[3] has recently been translated to scintillator applications due to the large stokes shift, near 200% PLQY in thin films,[4] high light yield, and energy-efficient conversion of thermalized charge carriers to NIR photons.[5], [6]

An as-of-yet unexplored application for this promising optoelectronic material platform is in an integrated, indirect gammavoltaic or X-ray-voltaic device.[7] In such a device, a high-energy incident photon (e.g., radioisotope characteristic γ-rays or an X-ray source) is attenuated by a thick scintillator crystal and is converted to a large multiplicity of near-monochromatic, low-energy photons, characteristic of the luminescent Yb3+ dopant. A bandgap-tuned PV cell is optically coupled to absorb the emitted low-energy scintillation light. The absorbance onset of the PV cell is in resonance with the scintillation emission energy to minimize spectral losses and achieve a high power conversion efficiency.

Here we report preliminary work on the synthesis of polycrystalline CsPbCl3:Yb scintillator pellets and their application in an X-ray-voltaic device. We showcase the optoelectronic properties of this scintillator material and their dependence on Yb3+ dopant concentration. We also show a Shockley-Queisser theoretic analysis of the corresponding PV performance characteristics as a function of the PV bandgap energy, radiation intensity, and scintillation emission spectra. Lastly, we discuss the next steps for precise energy and dose rate-dependent light yield measurements, further optimization of the quantum cutting dynamics, and demonstration of an optimized prototype gammavoltaic device.