ISO 20351:2017

Overview - ISO 20351:2017 (Integrating sphere method for phosphor IQE)

ISO 20351:2017 specifies an absolute measurement method for the internal quantum efficiency (IQE) of phosphor powders used in white light-emitting diodes (LEDs), using an integrating sphere. The procedure targets phosphors excited by UV or blue light that emit visible light, and it can also be applied to phosphors for non-white LEDs (green, orange, pink, purple). The standard documents equipment configuration, calibration, sample preparation, measurement steps, calculations and reporting to reduce inter-lab variation in measured photoluminescence quantum efficiency.

Key topics and technical requirements

• Measurement principle: Absolute IQE measurement using an integrating sphere to capture excitation, emission and scattered light for photon-based calculations.
• Equipment configuration: Describes a light source unit (monochromator or laser), sample unit (cell and integrating sphere), detecting unit (spectrometer, detector, optics) and data processing.
• Optical requirements: Guidance on excitation spectral width (desirable half-width < 15 nm), beam diameter relative to sample area, and minimum sample thickness (at least 2 mm).
• Sample handling: Storage, pre-processing and filling of cells; use of cover glasses or lids; use of reference cells or white diffusers (e.g., barium sulfate or PTFE) for baseline measurements.
• Calibration & maintenance: Wavelength calibration of source and detector, spectral responsivity correction, maintenance of sphere walls and white diffusers to ensure stable reflectance.
• Measurement procedure: Steps for measuring light spectrum with and without the phosphor sample, handling secondary absorption and self-absorption effects.
• Calculations: Conversion to photon-number-based spectra, derivation of photoluminescence spectra, determination of relative absorbed and emitted photon numbers and calculation of internal quantum efficiency.
• Reporting: Requirements for documenting methods, equipment, conditions and results to support reproducibility.

Applications and who uses this standard

• Phosphor manufacturers and material scientists validating photoluminescence quantum efficiency of powders for LED lighting.
• LED device and lamp manufacturers assessing phosphor performance for white and colored LEDs.
• Test laboratories and quality-control teams performing standardized IQE measurements for product specification and R&D benchmarking.
• Researchers in solid-state lighting (SSL) and fine ceramics focusing on advanced ceramic phosphors.

Related standards

• Normative reference: CIE S 017/E:2011 (International Lighting Vocabulary).
• ISO/TC 206 work context: part of fine ceramics and advanced materials standards for LED component testing.

Keywords: ISO 20351:2017, internal quantum efficiency, integrating sphere, phosphor powders, white LED, photoluminescence quantum efficiency, IQE measurement, fluorescence spectrophotometer.