NOVELTY - Device that detects, converts and emits light of pre-selected wavelength comprises: substrate and first electrode layer on it; polymer matrix on electrode layer containing nanocrystals that absorb light, and light emitting member; and second electrode layer on matrix. Substrate and/or electrode layer(s) are transparent to incident and emitted light. The incident light produces a responsive photocurrent, and pumps light emitting member to emit responsive light.    USE - For detecting light in a pre-selected wavelength region, converting detected light into light of at least one pre-selected wavelength and emitting the light at, at least one pre-selected wavelength (claimed) e.g. broadband or spectrally-engineered devices with multi-color light emitters for color displays, white light emitters for illumination, infrared multi-wavelength emitters for coarse wavelength-division multiplexing and code-division multiple access.    ADVANTAGE - The device provides a spectrally-tailored multi-color emission by inclusion of several light emitting device structures in the form of colloidal quantum dots formed of semiconducting polymers and a mixture of different quantum nanocrystals, that result in electrical or electrical and optical stimulation of luminescence. The use of size-selective monodisperse nanocrystals that absorb, convert and emit at pre-selected wavelengths, provide narrow emission, absorption and modulation of linewidths, and hence allows the combination of different quantum dots having different pre-selected wavelengths in multiple layers and provides a broader spectral shape. The device is able to convert the light in an infrared or visible spectral region, into light in a visible wavelength region at a higher wavelength than wavelengths in the visible spectral region.    DETAILED DESCRIPTION - A device (D) that detects light in a pre-selected wavelength region, converts the detected light into light of at least one pre-selected wavelength and emits the light at, at least one pre-selected wavelength comprises: a substrate and a first electrically conducting electrode layer (L1) on the substrate; a polymer matrix located on (L1) containing a mixture of nanocrystals that include at least first nanocrystals which absorb light in a pre-selected wavelength range, and a light emitting member located in the polymer matrix that emits light at the at least one pre-selected wavelength; and a second electrically conducting electrode layer (L1a) located on the polymer matrix. At least one of the substrate, (L1) and (L1a) is substantially transparent to the light in the pre-selected wavelength range and light at the at least one pre-selected wavelength. When the light in the pre-selected wavelength range is incident on the polymer matrix, a photocurrent is responsively produced when a pre-selected voltage is applied between (L1) and (L1a), and acts to pump the light emitting member that responsively emits light at the at least one pre-selected wavelength. An INDEPENDENT CLAIM is included for a device (D1) comprises: a substrate and (L1) on the substrate; a first layer (L2) of nanocrystals located on (L1) that absorbs light in a pre-selected wavelength region; at least second layer (L2a) of at least second nanocrystals that emits light at the at least one pre-selected wavelength located on (L2); and (L1a) on (L2a). At least one of the substrate, (L1) and (L1a) is substantially transparent to the light in the pre-selected wavelength range and light at the at least one pre-selected wavelength. When the light in the pre-selected wavelength range is incident on (L2), a photocurrent is responsively produced when a pre-selected voltage is applied between (L1) and (L1a), and acts to pump the (L2a) that responsively emits light at the at least one pre-selected wavelength.