ISO 20351:2024

Overview

ISO 20351:2024 - "Fine ceramics (advanced ceramics, advanced technical ceramics) - Test method for optical properties of ceramic phosphors for white light-emitting diodes using an integrating sphere" defines standardized laboratory methods to measure the optical performance of ceramic phosphor powders used in white LEDs. The second edition retains an absolute integrating-sphere method for measuring internal quantum efficiency (IQE) and adds a substitution method (using reference materials characterized by ISO 23946) to determine external quantum efficiency (EQE) and absorptance. The standard targets measurements when phosphors are excited by UV or blue light and emit visible light.

Key topics and requirements

• Measurement scope: Optical characterization of ceramic phosphors for white LEDs - IQE, EQE and absorptance.
• Two complementary methods:
  • Absolute method (integrating sphere) for internal quantum efficiency.
  • Substitution method (integrating sphere with reference materials) for external quantum efficiency and absorptance; reference values traceable to ISO 23946.
• Apparatus and components: Detailed requirements for apparatus configuration, including light source unit, sample cell and diffuser, integrating sphere, directing optics, spectrometer/detector, amplifier and data processing.
• Calibration and maintenance: Procedures for wavelength calibration, spectral responsivity correction, integrating sphere and diffuser inspection, and cell handling to ensure repeatable results.
• Sample preparation: Guidance on reference materials, storage, pre-processing and filling cells with ceramic phosphor powders.
• Measurement procedures: Step-by-step instructions for measurement environments, spectral acquisition (with and without phosphor), conversion to photon-number spectra, calculation of fluorescence spectra, IQE, EQE and absorptance.
• Reporting: Required data and formats for test reports to support comparability and traceability.

Applications and users

ISO 20351:2024 is practical for:

• Phosphor manufacturers validating product performance and comparing materials.
• LED and SSL (solid-state lighting) developers selecting phosphors for color rendering and luminous efficiency.
• Test laboratories and QA/QC teams performing routine and accredited measurements for product specifications.
• R&D groups and materials scientists characterizing new ceramic phosphors and optimizing formulations.
• Regulatory and standards bodies harmonizing optical property reporting across suppliers.

Benefits include standardized, repeatable measurements for product qualification, competitive benchmarking, and integration with quality management and certification workflows.

Related standards

• ISO 23946 - gonio-spectrofluorometer methods and reference-material characterization (used for substitution method reference values).
• ISO 13915 - substitution measurement methods using fluorescence spectrophotometers (contextual relevance).
• CIE S 017/E:2020 - international lighting vocabulary referenced for definitions.

Keywords: ISO 20351:2024, integrating sphere, ceramic phosphors, white LEDs, internal quantum efficiency, external quantum efficiency, absorptance, ISO 23946.