We propose a non-contact measurement method for determining two-dimensional (2D) temperature distribution of light-emitting diodes (LEDs). This method is based on both micro-hyperspectral imaging technology and reflected light method, owning merits of both high efficiency and high spatial resolution. Blue and green bare LEDs are used as LED under test, while red and near-infrared LEDs provide incident light to avoid spectral overlapping so as to reduce measurement error. During data processing, the convolution linear filtering algorithm is employed to improve the measurement accuracy. This proposed method is compared with the micro-thermocouple and infrared thermal imaging, with their respective comparison results in fairly good agreements. For spatial resolution of 2D temperature distribution, this method increases at least one order of magnitude compared with the thermal imaging method.

Two-dimensional temperature distribution measurement of light-emitting diodes by micro-hyperspectral imaging-based reflected light method.

We propose a non-contact method for determining phosphor/silicone temperature (phosphor temperature) in phosphor-coated light-emitting diode (pc-LED). The pc-LED with a surface mounted device (SMD) structure is primarily consisted of InGaN/GaN blue LED chip, (Sr,Ca)AlSiN3:Eu2+ red rare-earth phosphor, and transparent dimethyl silicone. This proposed method is basically based on a linear temperature dependence of divisional normalized emission power for phosphor/silicone mixture. Four types of pc-LED corresponding to four different phosphor concentrations are examined by proposed method. A comparison of measured results between micro-thermocouple device and proposed method has also been carried out, showing a fairly good agreement between them, except for pc-LED with 4.8 wt% phosphor concentration. We suggest that this proposed method can provide a useful tool for further study of optical and thermal characteristics in pc-LED.

Determining Phosphor Temperature in Light-Emitting Diode Based on Divisional Normalized Emission Power

The intensive measures of luminescence in a GaN/InGaN multiple quantum well system are used to examine the thermodynamics and phenomenological structure. The radiative /nonradiative transitions along with absorbed or emitted phonons that occur between the different quantum states of the electrons and holes associated with these processes make the quantum efficiency of a semiconductor nanosystem in an equilibrium state an extensive property. It has long been recognized that tuning of the indium (In) composition in InGaN interlayers gives the potential to obtain a spectrum in the near-infrared to near-ultraviolet spectral range. The thermodynamic intensive properties, including the Debye temperature, carrier temperature, and junction temperature, are the most appropriate metrics to describe the optical-related interactions inherent in a given heterostructure and so can be used as the state variables for understanding the quantum exchange behaviors. The energetic features of the quantum processes are characterized based on analysis of the intensive parameters as determined by means of electroluminescence (EL) and photoluminescence (PL) spectroscopy and current-voltage measurement and then correlated with the designed InGaN/GaN microstructures. According to the McCumber-Sturge theory, the EL and PL Debye temperatures obtained experimentally signal the strength of the electron-phonon and photon-phonon interaction, respectively, while the EL and PL carrier/junction temperatures correspond to the carrier localization. Higher EL Debye temperatures and lower EL carrier/junction temperatures reflect significantly higher luminescence quantum yields, indicative of electron-phonon coupling in the transfer of thermal energy between the confined electrons and the enhancement by excited phonons of heat-assisted emissions. On the other hand, the observation of low luminescence efficiency, corresponding to the lower PL Debye temperatures and higher PL carrier/junction temperatures, is attributed to photon-phonon coupling. These findings are in good accordance to the dependence of the EL and PL quantum efficiency on the In-content of the InGaN/GaN barriers, suggesting that the characteristic Debye and carrier/junction temperatures are intensive parameters useful for assessing the optical properties of a nano-engineered semiconductor heterostructure.

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Intensive measures of luminescence in GaN/InGaN heterostructures

The invention discloses a measuring method and measuring device for photometric and colorimetric parameters of a micro region of a luminescent device, and relates to the field of measurement of the photometric and colorimetric parameters of the luminescent device. The measuring device for the photometric and colorimetric parameters of the micro region of the luminescent device comprises a radiancelight source calibration system and a microscopic hyperspectral imaging test system; and the radiance light source calibration system comprises a spectrometer, a spectral radiance probe, an integrating sphere and a halogen tungsten lamp light source; the microscopic hyperspectral imaging test system comprises a hyperspectral imager, a microscope, a temperature control power supply and a driving power supply. The measuring method comprises the following steps: firstly, acquiring a spectral radiance distribution calibration file of a uniform luminous plane, then calibrating the microscopic hyperspectral imaging test system, and finally testing and calculating the photometric and colorimetric parameters of a sample to be measured. The measuring method and the measuring device can solve the problems on measurement and analysis of the photometry, the colorimetry and the uniformity of a two-dimensional surface of the luminescent device or a microdisplay array, and quickly and comprehesivelydetect the luminous quality of the device.

Measuring method and measuring device for photometric and colorimetric parameters of micro region of luminescent device

The invention provides a fluorescent sheet emitted light performance test apparatus and method. A temperature control apparatus consists of a temperature control base and a top cover which are arranged in a laminating manner, wherein the top cover is provided with a plurality of installation grooves at intervals along the length direction, and an LED exciting light source is arranged in each groove; the top cover is externally connected with a constant-current source and integrated with a circuit for driving the LED exciting light source; the temperature control base contacts the LED excitinglight source in a heat conducting manner; the constant-current source drives the LED exciting light source to emit exciting light; a plurality of fluorescent sheets are arranged on a fluorescent sheetbase, a motion controller controls one of the plurality of fluorescent sheets to move into a transmission path of the exciting light, so that the emitted by the fluorescent sheet 2 after being excited by the exciting light is received by a probe and transmitted to a CCD spectrometer; the CCD spectrometer 4 converts a light signal to an electric signal and transmits the electric signal to a computer; and the computer processes the electric signal from the CCD spectrometer, so that the spectrum acquisition and data analysis of the light emitted by the fluorescent sheet can be realized.

Fluorescent sheet emitted light performance test apparatus and method based on multichannel probe

The invention discloses a transmission-type test device and method for the variable-temperature spectral characteristic of white-light LED (Light-Emitting Diode) fluorescent powder, and relates to the field of LED fluorescent powder testing. The testing device is provided with an aluminum cylinder, graphene glass, a convex lens, a fluorescent powder temperature control circuit device, an LED blue-light chip, an LED chip temperature control device, an integrating sphere, a spectrometer and a computer. The fluorescent powder temperature control circuit device is introduced into the testing device, so that the technical blank of variable-temperature spectral characteristic testing of the fluorescent powder is filled up. The transmission-type testing method conforms to the working mode and principle of a white-light LED. The convex lens is used for converging blue light into parallel light, so that uniform distribution of excitation light is improved. The integrating sphere is used for collecting light, so that leakage of light is reduced, and the reliability of measured data is improved. A fluorescent powder temperature control point is separated from the integrating sphere, and heat insulating treatment is performed between the integrating sphere and the aluminum cylinder, so that the influence of temperature on the integrating sphere is avoided. The temperatures of an LED chip and the fluorescent powder are controlled respectively, so that the spectral characteristics under different conditions can be tested.

Transmission-type testing device and method for variable-temperature spectral characteristic of white-light LED (Light-Emitting Diode) fluorescent powder

Theories of spontaneous emission rates and carrier recombination mechanisms for multiple-quantum-well InGaN-based blue light-emitting diodes (LEDs) have been carefully studied. A relationship among the optical power, the current density, and the temperature (heat-sink temperature or p-n junction temperature) is identified, and an optical-electrical-thermal model (OETM) is proposed. Thereafter, spectral measurements have been carried out to confirm the validity of this OETM. Results show that measured optical powers under various current densities and heat-sink temperatures agree satisfactorily with those determined by the OETM. Furthermore, the traditional forward-voltage method (FVM) has also been carried out for comparison. Junction temperatures determined by this OETM is in accordance with those measured by the FVM. Therefore, this model can serve as an alternative tool for fast estimating junction temperatures after relevant fitting coefficients having been determined.

On a relationship among optical power, current density, and junction temperature for InGaN-based light-emitting diodes

We propose a transmission-type measurement system for determining temperature-dependent optical characteristics (TDOCs) for phosphors or remote phosphor plateswhich are applied in high-powerwhite light-emitting diodes, related to their stabilities and reliabilities. The proposed measurement system possesses remote-excitation characteristics and is able to separately control the temperature of tested phosphors or remote phosphor plates and that of excitation light sources (with the emission wavelength of 360–470 nm), to avoid the heat interference between them. This system is finally examined by fabricating two types of remote phosphor plates, i.e., yellow Y3Al5O12:Ce3+ and red CaAlSiN3:Eu2+ remote phosphor plates. A comparison between the proposed transmission-type system and the reflection-type system at various temperatures is also carried out. Results show that both the phosphor quantum efficiency and phosphor conversion efficiency of remote phosphor plates under various temperatures are possibly overestimated by the traditional reflection-type system. Employing the proposed method and carrying out experiments, we discover that the fraction of silicone in the silicone–phosphor mixture affects TDOCs of remote phosphor plates remarkably. Finally, via both the proposed system and the microhyperspectral imaging technology, thermal-quenching effects in the microcosmic level have also been investigated.

Determining Temperature-Dependent Optical Characteristics of Remote Phosphor Plates by Transmission-Type Measurement System

The invention relates to a three-primary-colour white light LED having a low circadian action factor, and relates to an LED. The three-primary-colour white light LED comprises a heat dissipation base, an encapsulation body, red light chips, a yttrium aluminium garnet fluorescent powder and silica gel mixed body, a lens, a reflection cup, a blue light LED chip and a metal electrode; the heat dissipation base, the red light chips, the reflection cup and the blue light LED chip are put in the encapsulation body; the red light chips and the blue light LED chip are put on the heat dissipation base; a blue light LED chip is arranged in the middle of the heat dissipation base; four red light chips are arranged around the blue light LED chip; the lens is encapsulation glass; silver is plated on the inner wall of the reflection cup; the yttrium aluminium garnet fluorescent powder and silica gel mixed body is uniformly coated on the lower surface of the lens; the yttrium aluminium garnet fluorescent powder and silica gel mixed body and the lens are put over the encapsulation body; furthermore, two ends of the lens are in sealed contact with the encapsulation body; the positive and negative electrodes of the red light chips are respectively guided onto the metal electrode in a lead bonding manner; and the metal electrode is embedded in the encapsulation body.

Qiu Haihua

Papers

Transmission-type testing device and method for variable-temperature spectral characteristic of white-light LED (Light-Emitting Diode) fluorescent powder

On a relationship among optical power, current density, and junction temperature for InGaN-based light-emitting diodes

Determining Temperature-Dependent Optical Characteristics of Remote Phosphor Plates by Transmission-Type Measurement System

Three-primary-colour white light LED having low circadian action factor